Study designs Flashcards
Key features of sample
Unbiased
Representative
Precise
Descriptive epidemiology
Sampling to infer back on population
hard to achieve perfect sample to represent population
Analytical epidemiology
Compare like for like samples
hard to achieve similar samples
Ecological study How?
Snapshot in time
Count cases by GROUPS (eg cases within a country)
Define characteristics (exposure and outcome)
Decide data involved - categorical or continuous
Measurement scales ecological study
Discrete/Qualitive - nominal (distinct categories) or ordinal (ordered categories)
Continuous/Quantitive - interval (meaningful differences) vs ratio
Issues for ecological studies
Definition of characteristics
Measurement variation
Confounding (ecological fallacy: falsely inferring individual association from group level association)
Chance (random error)
What is ecological fallacy?
falsely inferring individual association from group level association
Cross sectional studies
Snapshot of now Individual level (can be a series of studies over time)
Cross sectional survey, who are we generalising to?
Population
What population can w get access to CSS
Study population - GP practice?
How can we get access to population CSS
Sampling frame (census)
Who is in your study CSS?
The sample
Issues for cross sectional studies?
Sampling bias
Responder/participant bias
Chance - random error
Case control study
Find cases (eg diseased)
Find controls (eg not diseased)
Look back to past to find exposures
Compare
Issues with case control study
Selection bias (controls should reflect population and be comparable to cases)
Information bias (poor recall, missclassification)
Confounding
Chance - random error
