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Introduction to Clinical Epidemiology
Spring 1999 Elective
UT-H HSCJan Risser, PhD and Will Risser, MD PhD
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Epidemiology
Basic science concerned with the patterns of disease frequency in human population
Distribution of disease by person, place, time Assumption:
– Disease does not occur randomly – Disease has identifiable causes
» which can be altered and therefore
» prevent disease from developing
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Definition of Epidemiology
The study of the distribution and determinants of health-related states or events in specified population, and the application of this study to control of health problems. [source: Last (ed.) Dictionary of Epidemiology, 1995]
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Definition of Epidemiology
Study: surveillance, observation, hypothesis testing, analytic research, and experiments.
Distribution: analysis by time, place, and person.
Determinants: physical, biological, social, cultural, and behavioral factors that influence health.
Health-related states or events: diseases, causes of death, behavior, reactions to preventive regimens, and provision and use of health services.
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Definition of Epidemiology
Specified populations: those groups of people with identifiable characteristics
Application to control: refers to the goal of epidemiology, that is to assess the public health importance of diseases, identify the population at risk, identify the causes of disease,describe the natural history of disease, and evaluate the prevention and control of disease
Aims of epidemiologic research
Describe the health status of a population Explain the etiology of disease Predict the disease occurrence Control the disease distribution
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Preventable Causes of Disease
BEINGS Biological factors and Behavioral Factors Environmental factors Immunologic factors Nutritional factors Genetic factors Services, Social factors, and Spiritual factors[JF Jekel, Epidemiology, Biostatistics, and Preventive Medicine, 1996]
Causal model of risk factors for CVDCausal model of risk factors for CVD
Morbidity and Mortality(Stroke, MI)
Biological Risk Factors
(Hypertension, Blood Lipids, Homocysteine)
Genetic Risk Factors(Family History)
Behavioral Risk Factors(Cigarette, Diet, Exercise)
Environmental Factors(Socioeconomic Status, Work Environment)
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Epidemiology & Clinical Medicine
Epidemiology is used in clinical medicine to: describe the natural history of diseases discuss disease causality
- proximate: biological mechanisms of disease
- distal: social and environmental causes of disease provide disease surveillance
- essential for evaluating community health problems - - and setting disease control priorities
[Greenberg RS (ed.) Medical Epidemiology, 1993]
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Epidemiology & Clinical Medicine
Epidemiology is used in clinical medicine to: evaluate diagnostic testing
- evaluate usefulness, sensitivity, specificity
- to set cutoff points, and develop screening strategies
evaluate prognosis
- by identifying prognostic factors
- through cohort and case control studies
[Greenberg RS (ed.) Medical Epidemiology, 1993]
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Epidemiologic Process
In the epidemiologic process, researchers: – Define the problem: ask a well focused
question » hypothesis statement
– Identify the cause: test the hypothesis » is there an association between exposure and outcome
– Interpret the results: » threats to validity (bias, confounding),
» role of chance
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Brief History of EpidemiologyClassical Infectious Diseases Epidemiology
– Edward Jenner (1749-1823)
» developed a vaccine against smallpox using cow pox 160 years before virus was identified
– John Snow (1813-1858)
» described the association between dirty water and cholera 44 years before vibrio was identified
– Ignaz Semmelweis (1818-1865) » described the association between childbed fever and
physician’s unclean hands 32 years before causal agent was discovered
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Brief History of EpidemiologyClassical Nutritional Epidemiology
– James Lind (1716-1794) » conducted an experiment which showed that scurvy could
be treated and prevented with limes, lemons, and oranges ascorbic acid was discovered 175 years later
– Joseph Goldberger (1874-1927)» identified that pellagra was not infectious but nutritional
in origin and could be prevented by increasing the amount of animal products in the diet and substituting oatmeal for corn grits
niacin was discovered 10 years later
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Brief History of EpidemiologyEpidemiology of Chronic Diseases
Observational Studies:R Doll & AB Hill. Early case-control study. Smoking and carcinoma of the lung: Preliminary report. [Br. Med. J. 2:739, 1950]
Cohort Studies:An approach to longitudinal studies in a community: the Framingham study. 10,000 residents gave baseline information. Follow-up is now 50 years. [Annals New York Academy of Sciences 107:539;1963]
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Brief History of EpidemiologyEpidemiology of Chronic Diseases
Experimental Studies:
Hypertension Detection and Follow-up Program Cooperative Group. 10,500 subjects randomly assigned to two groups: 1. stepped care - antihypertensive therapy increased stepwise to achieve
and maintain blood pressure reduction to goal.
2. Referred care - subjects were referred to their primary care physician and
treated as usual.
mortality stepped care 9.0/100 referred care 9.7/100
final blood pressure 84.1 in stepped care 89.1 in referred care
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Brief History of EpidemiologyEpidemiology of Chronic Diseases
Physician Health Study– randomized, placebo-controlled, double-blind clinical trial
– conducted entirely through the mail
– 22,071 male physicians enrolled to study the effects of aspirin on cardiovascular disease and the effects of beta-carotene on cancer
– randomly assigned to one of four groups
aspirin beta carotene
active active
active placebo
placebo active
placebo placebo
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Observational and Analytical Epidemiology
Descriptive epidemiology– the occurrence of disease (cross-sectional)
Etiologic epidemiology (quasi-experimental)– cause of disease (cohort, case-control)
Experimental epidemiology– assessment of therapy (cohort, randomized clinical
trial)
Research Design Used in EpidemiologyResearch Design Used in Epidemiology
Case Reports / Case Series Case control Cohort: prospective or retrospective Cross sectional Qualitative (Randomized Clinical Trials) Secondary data analysis
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Definitions in Epidemiology
Bias Confounding Frequency Measures
– Prevalence
– Incidence
Measures of Association Causal Inference
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
BIAS
systematic errors in collecting or interpreting data such that there is deviation of results or inferences from the truth.
» selection bias: noncomparable criteria used to enroll participants.
» information bias: noncomparable information is obtained due to interviewer bias or due to recall bias
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
BIAS
Bias results from systematic flaws in study design, data collection, or the analysis or interpretation of
results.
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Selection BIAS
Selection bias
Hospital Mean duration Labor
deliveries of labor complications
Season
Summer 180 8.0 hr 7.8% (14/180)
Winter 240 10.5 hr 11.7% (28/240)
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Selection BIAS
DELIVERIES Mean duration Labor
Hospt. Home All of Labor Complications
Season
Summer 180 20 200 8.0 hr 8.0% (16/200)
Winter 240 160 400 8.0 hr 8.0% (32/400)
Home deliveries were more common in winter. Labor complications among home deliveries were low. Women with prolonged or complicated labor attempt to reach the hospital no matter what season.
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Information BIAS
Response bias - a systematic error that results when subjects respond inaccurately to an investigator’s questions
Lushton County Medical Society commissioned a survey of community perceptions regarding physician impairment by alcohol or drugs. [Biomedical Bestiary. Michael, Boyce & Wilcox]
Persons were asked for anonymous impressions regarding their
personal physician.
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Information BIAS
1000 persons were randomly chosen from the community and sent a simple postcard1. Is your physician’s medical judgment
ever compromised by the use of alcohol or drugs? 0.4%
2. Does the physician drug or alcohol abuse threaten the
professional image of physicians in Lushton? 78%
3. Are physicians who use drugs or alcohol a threat
to their patients? 85%
98% response rate
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Information BIAS
1000 original respondents re-interviewed after 12% of the licensed physicians in the county were cited for drug- or alcohol-related malpractice. 1. Is your physician’s medical judgment ever compromised by the
use of alcohol or drugs? [0.4%] 8%
2. Does the physician drug or alcohol abuse threaten the
professional image of physicians in Lushton? [78%] 80%
3. Are physicians who use drugs or alcohol a threat
to their patients? [85%] 82%
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Confounding
a mixing of effects » between the exposure, the disease, and other factors
associated with both the exposure and the disease
» such that the effects the effects of the two processes are not separated.
Jan Risser,
PhD Will
Risser, MD PhD
Confounding
Confounding results when the effect of an exposure on the disease (or outcome) is distorted because of the association of exposure with other factor(s) that influence the outcome under study.
Spring, 1999
Jan Risser,
PhD Will
Risser, MD PhD
Confounding [Biomedical Bestiary: Michael, Boyce & Wilcox, Little Brown. 1984]
Gambling Cancer
Smoking, Alcohol, other Factors
Observed association, presumed causation
Unobserved associationTrue association