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Quantitative Research
Richard Peacock, Clinical Librarian
Archway Healthcare Library
Ziba Nadimi, Outreach and Information Skills Librarian Camden Primary Care Trust
Definition
A study that aims to quantify attitudes or behaviours, measure variables on which they hinge, compare, and point out correlations. It is most often conducted via a survey on a sampling that must be representative so that the results can be extrapolated to the entire population studied. It requires the development of standardised and codifiable measurement instruments (structured questionnaires).
Ipsos- A Market Research Co.
Quantitative Data Collection
• Requires a specific protocol • Protocol is specified in advance of data
collection• Population and sample should be large.
The larger the better
Data Analysis
• Statistical analysis• Describes trends, compares groups,
relates variables• Compares your results with past research
The Anatomy of a Research Paper
• Introduction• Methods• Results• Discussion
The Anatomy of a Research Paper cont.
• The introduction summarises the background to the study
• The methods helps to understand if you are critically appraising a paper
• The results reports findings objectively without speculation or interpretation
• In the discussion the authors interpret the findings in light of the study design and other research
Levels of Evidence
Primary Research
Experimental
observational
SecondaryResearch
For qualitative studies? No consensus about the relative rigour of different methods
Systematic reviews &
Meta-analyses
Randomised controlled trials
Cohort studies
Case control studies
Case series
For quantitative studies
Systematic Review
• Identifies an intervention for a specific disease or other problem in health care
• Determines whether or not this interventions works• Authors locate, appraise and synthesise evidence
from as many relevant scientific studies as possible• They summarise conclusions about effectiveness• They provide a collation of the known evidence on a
given topic• Statistical methods (meta-analysis) may or may not
be used to analyse and summarise the results
Advantages of Systematic Reviews• Adhere to a strict design, therefore minimise
the chance of bias• Provide a scientific rather than subjective
summarisation of literature• Large amounts of information can be
assimilated quickly by healthcare providers, researchers, and policymakers
• Compare results of different studies to establish generalisability of findings and consistency of results
Disadvantages of Systematic Reviews• Experts may select only supportive evidence• Papers with more interesting result more
likely to be published• SRs may be biased due to exclusion of
relevant studies and inclusion of inadequate studies
• SRs include an element of judgement, whatever method is used e.g. authors of tobacco industry affiliated reviews are more likely to conclude that passive smoking is not harmful
Randomised Controlled Trials- RCTs
• Two or more interventions are compared by being randomly allocated to participants
• Includes a control intervention or no intervention
• If possible should be single/ double/ triple blinded
Blinding in RCTs
• Preventing those involved in a trial from knowing to which comparison group, i.e. experimental and control, a particular participant belongs
• The risk of bias is minimised• Participants, caregivers, outcome assessors
and analysts can all be blinded• Blinding of certain groups is not always
possible, e.g. surgeons in surgical trials• Single, double and triple blind are in common
use
Cohort Studies
• An observational study• A defined group of people (the cohort) is
followed over time• Outcomes are compared to examine people
who were exposed or not exposed to a particular intervention
• A retrospective cohort study identifies subjects from past records and follows them to the present
• A prospective cohort study assembles participants and follows them into the future
Case Control Studies
• Compares people with a specific disease or outcome of interest (cases) to people from the same population without that disease or outcome (control)
• Seeks associations between the outcome and prior exposure to particular risk factors e.g. one group may have been exposed to a particular substance that the other was not
• They are usually retrospective
Case Series
• A study reporting observations on a series of individuals, usually all receiving the same intervention, with no control group.
Odds-Ratio Diagram (Blobbogram)
Odds-Ratio Diagram Cont.
• Included in CDSR and other good systematic reviews
• Presents complicated results and concepts in a clear visual format
• For each individual trial, the odds-ratio result is represented by a box
• The vertical line is an odds-ratio of one known as “line of no effect”
• The horizontal line is the “confidence interval” for that result
Odds-Ratio Diagram Cont.
• Confidence Interval - the range in which we are 95% or 99% confident that the ‘real’ result of the study lies when is extrapolated to the whole of the population sampled in the study
• The diamond is called meta analysis – the statistical method of combining the results of different RCTs for the same intervention
Odds-Ratio Diagram Cont.
• Results to the left of the line of no effect = less of the outcome in the experimental group
• Results to the right of the line of no effect = more of the outcome in the experimental group
• It is important to note whether the outcome is good or bad
Odds-Ratio Diagram Cont.
• If CI crosses line of no effect = inconclusive results
• Longer CI = smaller study (less confident of results)
• Shorter CI = bigger study (more confident of results)
P Values
• P for probability (ranging from zero to one)• The result could have occurred by chance if
in reality the null hypothesis was true• The null hypothesis- the factor of interest
(e.g. treatment) has no impact on outcome (e.g. risk of death)
• P value of less than 0.05 means likelihood of results being due to chance is less than 1 in 20 = “Statistically significant”
ReferencesMcGovern, D.P.B. etal, Evidence-based medicine, BIOS Scientific Publishers Ltd., 2001
Greenhalgh, T., How to read a paper, 3rd ed., BMJ Publishing Group, 2006
Kelsey, K.D., (Lecture 2) Quantitative and qualitative approaches to research- PowerPoint Presentation
Ward, L., Critical reading made easy:effectiveness and experience, University Hospitals of Leicester NHS Trust- PowerPoint Presentation
Jackson, N., Conducting systematic reviews of public health and health promotion interventions, Cochrane Health Promotion and Public Health Field- PowerPoint Presentation
The Cochrane Library’s Glossary of Terms, Wiley InterScience
Andrew Hayward, Critical Appraisal of Analytical Studies- PowerPoint Presentation
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