Study Design Flashcards
Internal Validity
Validity within the confines of the study methods.
Does the study design adequately and appropriately test/measure what it purports?
Does the study adequately and appropriately address bias, confounding, and measurement of end points?
Nuts and bolts of the study methods
External Validity
Validity related to generalizing the study results outside of the study
Can the results be applied to other groups?
What is bias?
Systematic, non-random variation in study methodology and conductance.. introducing error in interpretation
Selection vs observation or information bias?
Selection- Arise form selection of subjects (sample)
Information- asking someone to remember what med they took 25 years ago
What is confounding?
Can confuse or cloud a variable of interest.
Example: Smoking, passive smoke exposure and lung cancer
May hide or exaggerate a true association
How do you control for confounding?
Randomization, Restriction, Matching, Stratification, Multivariate analysis
What’s the hierarchy of study designs?
Systematic reviews and meta analysis –> RCT –> Cohort –> Case-control–> Cross sectional–> Case series –> Opinions
What are case reports or case series?
Document and describe experiences, novel treatments, and unusual events.
Useful for hypothesis generations. QT interval prolongation associated with FQ antibiotics.
Is IRB approval required?
What is a case control study?
Determine the association between exposures (risks) and disease (condition).
Example is aspirin use and Reye’s syndrome.
Often referred to as retrospective studies, useful to study exposures in rare disease or ones that take long periods to develop.
What are some advantages of case-control studies?
Advantages- Inexpensive and can be conducted quickly. Allows investigation of multiple possible exposures/association.
What are some disadvantages of case-control studies?
Confounding must be controlled for. Observation and recall bias: looking back to remember. Selection bias: Case selection and control matching is difficult
What is the measure of association for case-control studies?
Odds ratio.
What are cohort studies?
Determine the association between exposures/factors and disease/condition development. Estimation of the risk of outcome (RR between exposure groups) and study outcome of interest in those with and without an exposure.
Describes the incidence or natural history of a disease/condition and measures it in time sequence
What are some advantages of a retrospective cohort study?
Less expensive and time-consuming, not loss to to follow-up, ability to investigate issues not amenable to a clinical trial or ethical or safety issues
