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8/13/2019 Cohort Study (a.n.p)
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Study Design 101 Helpful formulas
Finding specific study types Glossary
References
Meta-Analysis
SystematicReview
PracticeGuideline
RandomizedControlled Trial
Cohort Study Case Control Study
Case Report
Cohort Study
Definition
A study design where one or more samples (called cohorts) are followed prospectively andsubsequent status evaluations with respect to a disease or outcome are conducted to determine
which initial participants exposure characteristics (risk factors) are associated with it. As the study isconducted, outcome from participants in each cohort is measured and relationships with specificcharacteristics determined
Advantages
Subjects in cohorts can be matched, which limits the influence of confoundingvariables
Standardization of criteria/outcome is possible
Easier and cheaper than a randomized controlled trial (RCT)
Disadvantages
Cohorts can be difficult to identify due to confounding variables
No randomization, which means that imbalances in patient characteristics could exist
Blinding/masking is difficult
Outcome of interest could take time to occur
Design pitfalls to look out for
The cohorts need to be chosen from separate, but similar, populations.
How many differences are there between the control cohort and the experiment cohort? Will those differences
cloud the study outcomes?
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Fictitious Example
A cohort study was designed to assess the impact of sun exposure on skin damage in beachvolleyball players. During a weekend tournament, players from one team wore waterproof, SPF 35sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball
tournament players' skin from both teams was analyzed for texture, sun damage, and burns.Comparisons of skin damage were then made based on the use of sunscreen. The analysis showed asignificant difference between the cohorts in terms of the skin damage.
Real-life Example
Ramchand, R., Ialongo, N. S., & Chilcoat, H. D. (2007). The effect of working for pay on adolescenttobacco use.American Journal of Public Health, 97(11),2056-2062.
This study uses data collected from high school students from Baltimore, Maryland, and studies thedifferences in initiation of tobacco use between a cohort of adolescents that started working for payand a cohort of adolescents that did not work. The results suggest that adolescents who work for payhave a higher risk of initiating tobacco use.
Lindenauer, P. K., Rothberg, M. B., Pekow, P. S., Kenwood, C., Benjamin, E. M., & Auerbach, A. D.(2007). Outcomes of care by hospitalists, general internists, and family physicians. New England
Journal of Medicine, 357(25),2589-2600.
To study effects of hospitalists, general internists, and family physicians on patient care, patients thatwere hospitalized with certain conditions under the care of hospitalists, general internists, and familyphysicians were separated into three cohorts. The results showed that patients cared for byhospitalists had shorter hospital stays and lower costs than those cared for by general internists orfamily physicians.
Nichol, K. L., Nordin, J. D., Nelson, D. B., Mullooly, J. P., & Hak, E. (2007). Effectiveness of influenzavaccine in the community-dwelling elderly. New England Journal of Medicine, 357(14), 1373-1381.
To determine the long-term effectiveness of influenza vaccines in elderly people, cohorts ofvaccinated elderly and unvaccinated community-dwelling elderly were studied. The results suggestthat the elderly who are vaccinated have a reduced risk of hospitalization for pneumonia or influenza.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
Cohort
Confounding Variables
Population Bias/Volunteer Bias
Prospective Study
Now test yourself!
1. In a cohort study, an exposure is assessed and then participants are followed prospectively toobserve whether they develop the outcome.
http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effectiveness%20of%20influenza%20vaccine%20in%20the%20community-dwelling%20elderlyhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effectiveness%20of%20influenza%20vaccine%20in%20the%20community-dwelling%20elderlyhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effectiveness%20of%20influenza%20vaccine%20in%20the%20community-dwelling%20elderlyhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#prosstudyhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#prosstudyhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#prosstudyhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effectiveness%20of%20influenza%20vaccine%20in%20the%20community-dwelling%20elderlyhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effectiveness%20of%20influenza%20vaccine%20in%20the%20community-dwelling%20elderlyhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=%20Outcomes%20of%20care%20by%20hospitalists%2C%20general%20internists%2C%20and%20family%20physicians.http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20usehttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=The%20effect%20of%20working%20for%20pay%20on%20adolescent%20tobacco%20use8/13/2019 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a) True
b) False
2. Cohort Studies generally look at which of the following?
a) Determining the sensitivity and specificity of diagnostic methods
b) Identifying patient characteristics or risk factors associated with a disease or outcome
c) Variations among the clinical manifestations of patients with a disease
d) The impact of blinding or masking a study population
Study Design 101
Helpful formulas Finding specific study types
Glossary References
Meta-Analysis
SystematicReview
PracticeGuideline
Randomized
Controlled Trial Cohort Study
Case Control Study Case Report
Randomized Controlled Trial
Definition
A study design that randomly assigns participants into an experimental group or a control group. Asthe study is conducted, the only expected difference between the control and experimental groups ina randomized controlled trial (RCT) is the outcome variable being studied.
Advantages
Good randomization will wash out any population bias
Easier to blind/mask than observational studies
Results can be analyzed with well known statistical tools
Populations of participating individuals are clearly identified
Disadvantages
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Expensive in terms of time and money
Volunteer biases: the population that participates may not be representative of thewhole
Does not reveal causation
Loss to follow-up attributed to treatment
Design pitfalls to look out for
An RCT should be a study of one population only.
Was the randomization actually random, or are there really two populations being studied?
The variables being studied should be the only variables between the experimental group and thecontrol group.
Are there any confounding variables between the groups?
Fictitious Example
To determine how a new type of short wave UVA-blocking sunscreen affects the general health ofskin in comparison to a regular long wave UVA-blocking sunscreen, 40 trial participants wererandomly separated into equal groups of 20: an experimental group and a control group. Allparticipants' skin health was then initially evaluated. The experimental group wore the short waveUVA-blocking sunscreen daily, and the control group wore the long wave UVA-blocking sunscreendaily.
After one year, the general health of the skin was measured in both groups and statistically analyzed.In the control group, wearing long wave UVA-blocking sunscreen daily led to improvements in general
skin health for 60% of the participants. In the experimental group, wearing short wave UVA-blockingsunscreen daily led to improvements in general skin health for 75% of the participants.
Real-life Examples
Ensrud, K. E., Stock, J. L., Barrett-Connor, E., Grady, D., Mosca, L., Khaw, K., et al. (2008). Effects ofraloxifene on fracture risk in postmenopausal women: The raloxifene use for the heart trial. Journal of
Bone and Mineral Research, 23(1),112-120.
This research studied the effect of raloxifene on fracture risk in postmenopausal women, and foundthat the women who took raloxifene over the same five year period of time as the women who did notreduced their risk of clinical vertebrate fracture.
Krishna, S., Balas, E. A., Francisco, B. D., & Knig, P. (2006). Effective and sustainable multimediaeducation for children with asthma: A randomized controlled trial. Children's Health Care, 35(1),75-90.
This article reports on the effect of multimedia education for children with asthma. A control group ofpediatric patients with asthma was given standard asthma educational resources, while theexperimental group of pediatric patients with asthma was given standard resources plus multimediaresources. The study found a reduction in daily symptoms, in emergency room visits, in school daysmissed, and in days of limited activity in the group given multimedia education resources.
Mller, O., Traor, C., Kouyat, B., Y, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomized
controlled trial.Bulletin of the World Health Organization, 84(2),120-126.
http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum8/13/2019 Cohort Study (a.n.p)
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The study done in this example was to determine whether the early use of bed nets had an effect onthe morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets atbirth, and a control group of infants used bed nets at six months of age. Results showed no significantdifference in morbidity rates, but use of bed nets from birth was related to lower incidence of bothmalaria and moderate to severe anemia.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
Blinding/Masking
Causation
Confounding Variables
Correlation Double Blinding/Masking
Null Hypothesis
Population/Cohort
Population Bias/Volunteer Bias
Randomization
Research (alternative) Hypothesis
Sensitivity
Specificity
Type 1 error
Type 2 error
Now test yourself!1. Having a volunteer bias in the population group is a good thing because it means the studyparticipants are eager and make the study even stronger.
a) True
b) False
2. Why is randomization important to assignment in an RCT?
a) It enables blinding/masking
b) So causation may be extrapolated from results
c) It balances out individual characteristics between groups.
d) a and c
e) b and c
http://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rr8/13/2019 Cohort Study (a.n.p)
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Study Design 101
Helpful formulas Finding specific study types
Glossary References
Meta-Analysis
SystematicReview
PracticeGuideline
Randomized
Controlled Trial Cohort Study
Case Control Study Case Report
Randomized Controlled Trial
Definition
A study design that randomly assigns participants into an experimental group or a control group. Asthe study is conducted, the only expected difference between the control and experimental groups ina randomized controlled trial (RCT) is the outcome variable being studied.
Advantages
Good randomization will wash out any population bias
Easier to blind/mask than observational studies
Results can be analyzed with well known statistical tools
Populations of participating individuals are clearly identified
Disadvantages Expensive in terms of time and money
Volunteer biases: the population that participates may not be representative of thewhole
Does not reveal causation
Loss to follow-up attributed to treatment
Design pitfalls to look out for
An RCT should be a study of one population only.
Was the randomization actually random, or are there really two populations being studied?
http://www.gwumc.edu/library/tutorials/studydesign101/index.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/index.html8/13/2019 Cohort Study (a.n.p)
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The variables being studied should be the only variables between the experimental group and thecontrol group.
Are there any confounding variables between the groups?
Fictitious ExampleTo determine how a new type of short wave UVA-blocking sunscreen affects the general health ofskin in comparison to a regular long wave UVA-blocking sunscreen, 40 trial participants wererandomly separated into equal groups of 20: an experimental group and a control group. Allparticipants' skin health was then initially evaluated. The experimental group wore the short waveUVA-blocking sunscreen daily, and the control group wore the long wave UVA-blocking sunscreendaily.
After one year, the general health of the skin was measured in both groups and statistically analyzed.In the control group, wearing long wave UVA-blocking sunscreen daily led to improvements in generalskin health for 60% of the participants. In the experimental group, wearing short wave UVA-blocking
sunscreen daily led to improvements in general skin health for 75% of the participants.
Real-life Examples
Ensrud, K. E., Stock, J. L., Barrett-Connor, E., Grady, D., Mosca, L., Khaw, K., et al. (2008). Effects ofraloxifene on fracture risk in postmenopausal women: The raloxifene use for the heart trial. Journal of
Bone and Mineral Research, 23(1),112-120.
This research studied the effect of raloxifene on fracture risk in postmenopausal women, and foundthat the women who took raloxifene over the same five year period of time as the women who did notreduced their risk of clinical vertebrate fracture.
Krishna, S., Balas, E. A., Francisco, B. D., & Knig, P. (2006). Effective and sustainable multimediaeducation for children with asthma: A randomized controlled trial. Children's Health Care, 35(1),75-90.
This article reports on the effect of multimedia education for children with asthma. A control group ofpediatric patients with asthma was given standard asthma educational resources, while theexperimental group of pediatric patients with asthma was given standard resources plus multimediaresources. The study found a reduction in daily symptoms, in emergency room visits, in school daysmissed, and in days of limited activity in the group given multimedia education resources.
Mller, O., Traor, C., Kouyat, B., Y, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomizedcontrolled trial.Bulletin of the World Health Organization, 84(2),120-126.
The study done in this example was to determine whether the early use of bed nets had an effect onthe morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets atbirth, and a control group of infants used bed nets at six months of age. Results showed no significantdifference in morbidity rates, but use of bed nets from birth was related to lower incidence of bothmalaria and moderate to severe anemia.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum8/13/2019 Cohort Study (a.n.p)
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Blinding/Masking
Causation
Confounding Variables
Correlation
Double Blinding/Masking
Null Hypothesis
Population/Cohort Population Bias/Volunteer Bias
Randomization
Research (alternative) Hypothesis
Sensitivity
Specificity
Type 1 error
Type 2 error
Now test yourself!
1. Having a volunteer bias in the population group is a good thing because it means the studyparticipants are eager and make the study even stronger.
a) True
b) False
2. Why is randomization important to assignment in an RCT?
a) It enables blinding/masking
b) So causation may be extrapolated from results
c) It balances out individual characteristics between groups.
d) a and c
e) b and c
Study Design 101 Helpful formulas
Finding specific study types Glossary
References
Meta-Analysis
SystematicReview
http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/index.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/index.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blinding8/13/2019 Cohort Study (a.n.p)
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PracticeGuideline
RandomizedControlled Trial
Cohort Study Case Control Study
Case Report
Randomized Controlled Trial
Definition
A study design that randomly assigns participants into an experimental group or a control group. Asthe study is conducted, the only expected difference between the control and experimental groups ina randomized controlled trial (RCT) is the outcome variable being studied.
Advantages
Good randomization will wash out any population bias
Easier to blind/mask than observational studies
Results can be analyzed with well known statistical tools
Populations of participating individuals are clearly identified
Disadvantages
Expensive in terms of time and money Volunteer biases: the population that participates may not be representative of the
whole
Does not reveal causation
Loss to follow-up attributed to treatment
Design pitfalls to look out for
An RCT should be a study of one population only.
Was the randomization actually random, or are there really two populations being studied?
The variables being studied should be the only variables between the experimental group and thecontrol group.
Are there any confounding variables between the groups?
Fictitious Example
To determine how a new type of short wave UVA-blocking sunscreen affects the general health ofskin in comparison to a regular long wave UVA-blocking sunscreen, 40 trial participants wererandomly separated into equal groups of 20: an experimental group and a control group. Allparticipants' skin health was then initially evaluated. The experimental group wore the short waveUVA-blocking sunscreen daily, and the control group wore the long wave UVA-blocking sunscreendaily.
http://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.html8/13/2019 Cohort Study (a.n.p)
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After one year, the general health of the skin was measured in both groups and statistically analyzed.In the control group, wearing long wave UVA-blocking sunscreen daily led to improvements in generalskin health for 60% of the participants. In the experimental group, wearing short wave UVA-blockingsunscreen daily led to improvements in general skin health for 75% of the participants.
Real-life ExamplesEnsrud, K. E., Stock, J. L., Barrett-Connor, E., Grady, D., Mosca, L., Khaw, K., et al. (2008). Effects ofraloxifene on fracture risk in postmenopausal women: The raloxifene use for the heart trial. Journal of
Bone and Mineral Research, 23(1),112-120.
This research studied the effect of raloxifene on fracture risk in postmenopausal women, and foundthat the women who took raloxifene over the same five year period of time as the women who did notreduced their risk of clinical vertebrate fracture.
Krishna, S., Balas, E. A., Francisco, B. D., & Knig, P. (2006). Effective and sustainable multimediaeducation for children with asthma: A randomized controlled trial. Children's Health Care, 35(1),75-90.
This article reports on the effect of multimedia education for children with asthma. A control group ofpediatric patients with asthma was given standard asthma educational resources, while theexperimental group of pediatric patients with asthma was given standard resources plus multimediaresources. The study found a reduction in daily symptoms, in emergency room visits, in school daysmissed, and in days of limited activity in the group given multimedia education resources.
Mller, O., Traor, C., Kouyat, B., Y, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomizedcontrolled trial.Bulletin of the World Health Organization, 84(2),120-126.
The study done in this example was to determine whether the early use of bed nets had an effect onthe morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets atbirth, and a control group of infants used bed nets at six months of age. Results showed no significantdifference in morbidity rates, but use of bed nets from birth was related to lower incidence of bothmalaria and moderate to severe anemia.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
Blinding/Masking
Causation
Confounding Variables
Correlation
Double Blinding/Masking
Null Hypothesis
Population/Cohort
Population Bias/Volunteer Bias
Randomization
Research (alternative) Hypothesis
Sensitivity
Specificity Type 1 error
http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.ncbi.nlm.nih.gov/sites/entrez?orig_db=PubMed&db=pubmed&cmd=Search&TransSchema=title&term=Effects%20of%20insecticide-treated%20bednets%20during%20early%20infancy%20in%20an%20African%20area%20of%20intense%20malaria%20transmission%3Ahttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#rrhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.html#orhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#blindinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#causationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#confoundinghttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#correlationhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#doubleblindhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#nullhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#cohorthttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#popbiashttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#randomhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type1http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#specificityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#sensitivityhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#hypothhttp://www.gwumc.edu/library/tutorials/studydesign10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Cohort Study (a.n.p)
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Type 2 error
Now test yourself!
1. Having a volunteer bias in the population group is a good thing because it means the study
participants are eager and make the study even stronger.
a) True
b) False
2. Why is randomization important to assignment in an RCT?
a) It enables blinding/masking
b) So causation may be extrapolated from results
c) It balances out individual characteristics between groups.
d) a and c
e) b and c
Study Design 101 Helpful formulas
Finding specific study types Glossary
References
Meta-Analysis
SystematicReview
PracticeGuideline
RandomizedControlled Trial
Cohort Study Case Control Study
Case Report
Randomized Controlled Trial
Definition
http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type2http://www.gwumc.edu/library/tutorials/studydesign101/index.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casereports.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/casecontrols.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/cohorts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/practiceguidelines.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/systematicreviews.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/metaanalyses.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/references.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/glossary.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/howtofind.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/formulas.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/index.htmlhttp://www.gwumc.edu/library/tutorials/studydesign101/rcts.html#type28/13/2019 Cohort Study (a.n.p)
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This research studied the effect of raloxifene on fracture risk in postmenopausal women, and foundthat the women who took raloxifene over the same five year period of time as the women who did notreduced their risk of clinical vertebrate fracture.
Krishna, S., Balas, E. A., Francisco, B. D., & Knig, P. (2006). Effective and sustainable multimediaeducation for children with asthma: A randomized controlled trial. Children's Health Care, 35(1),75-90.
This article reports on the effect of multimedia education for children with asthma. A control group ofpediatric patients with asthma was given standard asthma educational resources, while theexperimental group of pediatric patients with asthma was given standard resources plus multimediaresources. The study found a reduction in daily symptoms, in emergency room visits, in school daysmissed, and in days of limited activity in the group given multimedia education resources.
Mller, O., Traor, C., Kouyat, B., Y, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomizedcontrolled trial.Bulletin of the World Health Organization, 84(2),120-126.
The study done in this example was to determine whether the early use of bed nets had an effect on
the morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets atbirth, and a control group of infants used bed nets at six months of age. Results showed no significantdifference in morbidity rates, but use of bed nets from birth was related to lower incidence of bothmalaria and moderate to severe anemia.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
Blinding/Masking
Causation
Confounding Variables
Correlation
Double Blinding/Masking
Null Hypothesis
Population/Cohort
Population Bias/Volunteer Bias
Randomization
Research (alternative) Hypothesis
Sensitivity
Specificity Type 1 error
Type 2 error
Now test yourself!
1. Having a volunteer bias in the population group is a good thing because it means the studyparticipants are eager and make the study even stronger.
a) True
b) False
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2. Why is randomization important to assignment in an RCT?
a) It enables blinding/masking
b) So causation may be extrapolated from results
c) It balances out individual characteristics between groups.
d) a and c
e) b and c
Study Design 101 Helpful formulas
Finding specific study types Glossary
References
Meta-Analysis
SystematicReview
PracticeGuideline
RandomizedControlled Trial
Cohort Study Case Control Study
Case Report
Randomized Controlled Trial
DefinitionA study design that randomly assigns participants into an experimental group or a control group. Asthe study is conducted, the only expected difference between the control and experimental groups ina randomized controlled trial (RCT) is the outcome variable being studied.
Advantages
Good randomization will wash out any population bias
Easier to blind/mask than observational studies
Results can be analyzed with well known statistical tools
Populations of participating individuals are clearly identified
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Disadvantages
Expensive in terms of time and money
Volunteer biases: the population that participates may not be representative of thewhole
Does not reveal causation Loss to follow-up attributed to treatment
Design pitfalls to look out for
An RCT should be a study of one population only.
Was the randomization actually random, or are there really two populations being studied?
The variables being studied should be the only variables between the experimental group and thecontrol group.
Are there any confounding variables between the groups?
Fictitious Example
To determine how a new type of short wave UVA-blocking sunscreen affects the general health ofskin in comparison to a regular long wave UVA-blocking sunscreen, 40 trial participants wererandomly separated into equal groups of 20: an experimental group and a control group. Allparticipants' skin health was then initially evaluated. The experimental group wore the short waveUVA-blocking sunscreen daily, and the control group wore the long wave UVA-blocking sunscreendaily.
After one year, the general health of the skin was measured in both groups and statistically analyzed.In the control group, wearing long wave UVA-blocking sunscreen daily led to improvements in generalskin health for 60% of the participants. In the experimental group, wearing short wave UVA-blockingsunscreen daily led to improvements in general skin health for 75% of the participants.
Real-life Examples
Ensrud, K. E., Stock, J. L., Barrett-Connor, E., Grady, D., Mosca, L., Khaw, K., et al. (2008). Effects ofraloxifene on fracture risk in postmenopausal women: The raloxifene use for the heart trial. Journal of
Bone and Mineral Research, 23(1),112-120.
This research studied the effect of raloxifene on fracture risk in postmenopausal women, and foundthat the women who took raloxifene over the same five year period of time as the women who did notreduced their risk of clinical vertebrate fracture.
Krishna, S., Balas, E. A., Francisco, B. D., & Knig, P. (2006). Effective and sustainable multimediaeducation for children with asthma: A randomized controlled trial. Children's Health Care, 35(1),75-90.
This article reports on the effect of multimedia education for children with asthma. A control group ofpediatric patients with asthma was given standard asthma educational resources, while theexperimental group of pediatric patients with asthma was given standard resources plus multimediaresources. The study found a reduction in daily symptoms, in emergency room visits, in school daysmissed, and in days of limited activity in the group given multimedia education resources.
http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.informaworld.com/smpp/content~content=a783764394http://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSumhttp://www.ncbi.nlm.nih.gov/pubmed/17892376?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum8/13/2019 Cohort Study (a.n.p)
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Mller, O., Traor, C., Kouyat, B., Y, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomizedcontrolled trial.Bulletin of the World Health Organization, 84(2),120-126.
The study done in this example was to determine whether the early use of bed nets had an effect onthe morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets at
birth, and a control group of infants used bed nets at six months of age. Results showed no significantdifference in morbidity rates, but use of bed nets from birth was related to lower incidence of bothmalaria and moderate to severe anemia.
Related Formulas
Relative Risk
Odds Ratio
Related Terms
Blinding/Masking
Causation
Confounding Variables
Correlation
Double Blinding/Masking
Null Hypothesis
Population/Cohort
Population Bias/Volunteer Bias
Randomization
Research (alternative) Hypothesis
Sensitivity
Specificity
Type 1 error
Type 2 error
Now test yourself!
1. Having a volunteer bias in the population group is a good thing because it means the studyparticipants are eager and make the study even stronger.
a) True
b) False
2. Why is randomization important to assignment in an RCT?
a) It enables blinding/masking
b) So causation may be extrapolated from results
c) It balances out individual characteristics between groups.
d) a and c
e) b and c
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