41 - Observational Studies in CVD Flashcards
Cross-sectional studies
Sample of population, taken at one point in time (non-longitudinal)
Data taken from questionnaires, examinations, investigations, etc.
Drawbacks of cross-sectional studies
Can’t really prove causation, as have no temporal component.
Advantages of cross-sectional studies
Cheap, fast, relatively easy
Case-control studies
Compare previous exposure status to risk factor between those known to have outcome (cases), and those without outcome (controls).
Non-longitudinal.
Steps in case-control studies
1)
2)
1) Match cases and controls according to confounders (age, sex, etc).
2) Determine previous exposure among subjects
Study type that is useful for studying rare outcomes
Case-control studies
Why are case-control studies useful for studying rare outcomes?
Can select cases who have rare condition, instead of recruiting a large enough group of people to study so that one of them might develop condition
Key output of case-control studies
Odds ratio (approximation of relative risk)
Why is the key output of case-control studies an odds ratio, and not a relative risk?
Case-control studies are non-longitudinal. Relative risk requires longitudinal data to generate (relative risk is rate exposed/rate unexposed, and rate is the probability of disease occurring in an undiseased population over cumulative time of study).
How is odds ratio calculated?
[odds of exposure to non-exposure among cases] ÷
[odds of exposure to non-exposure among controls]
Cohort studies
Longitudinal studies.
Compare outcomes among subgroups (EG: disease in exposed/unexposed).
Collect incidence data
Data output of cohort studies
Relative risk
Difference between prospective and retrospective cohort study
Prospective is where subjects are recruited before outcome has occurred.
Retrospective is where subjects are recruited after outcome has occurred.
Advantages of cohort studies
explicit (often-detailed) knowledge about temporal
relationship between exposure and outcome
• can include multiple exposures and outcomes
• research hypotheses can be addressed post hoc in
established cohorts
Disadvantages of cohort studies
1) Hard to study rare outcomes
2) Difficult to carry out, expensive