Epidemiology Flashcards
Name three advantages and disadvantages of case control studies.
Time efficient, efficient for rare or long latency diseases, several exposure assessment.
Not efficient for rare exposures, retrospective recall bias, difficult to temporally clarify.
What is advantageous in cohort studies.
rare exposures, multiple effects of SAME exposures, examine causality, direct estimate of risk.
Fill out questionnaire then follow you.
Why are cohort studies sometimes not suitable?
expensive, unsuitable for rare disease, time, difficult to interpret if loss to follow up is high.
What three types of populations are used in studies?
Target (want to make inferences about them)
Source (study population drawn from here)
Study (serve as study participants)
What is validity and how do internal and external validity differ?
Validity = lack of bias Internal = validity of inferences as they pertain to members of the source population. External = validity as they pertain to members outside the population.
What are self selection and diagnostic bias?
Self-selection = (healthy worker effect) - survey respondents allowed to decide whether to participate.
Diagnostic = Outcome more likely to be ascertained as consequence of a particular exposure. (e.g. doctors aware of a relationship).
What is recall bias?
A problem in case control studies when cases recall past exposures differently than controls.
Cases and controls must have same recall period.
What is confounding?
Apparent effect of exposure of interest distorted due to effect of extraneous factor (confounder) being mistaken or mixed with actual exposure (which may be null) –> bias.
What are the criteria for confounding factors?
- Must be a risk factor for disease.
- Must be associated with EXPOSURE under study in the source population.
- Must not be affected by exposure or disease. (can’t be be an INTERMEDIATE FACTOR).