TYPES OF STUDIES EPIDEMIOLOGY Flashcards
(21 cards)
What is a cohort study?
A study where individuals are defined according to the presence or absence of an exposure of interest
What are the advantages of a cohort study?
- Determine temporal sequence between exposure + outcome
- Can examine multiple outcomes from an exposure
- Can calculate incidence (+ therefore relative risk + risk difference)
- Good for rare exposures
What are the limitations of a cohort study?
- Loss to follow up – can lead to bias if related to exposure + outcome= bias -
- Potential for misclassification of exposures/outcomes
- Generally, not good for studying rare outcome
- Time consuming
- Can be expensive
what types of study is cross sectional study?
- descriptive and observational
what does cross-sectional study calculate?
prevalence
- the proportion of a defined population who have a disease a a given point in time
what can the findings of cross-sectional study be used for?
- we don’t know if the exposure or outcome came first as they were both assessed at the same time so the findings can only be used for hypothesis generation.
what are the strengths of cross sectional studies?
- assess multiple exposures and outcomes
- can be used to calculate prevalence, distribution of prevalence in population and hypothesis generation
- inexpensive and quick
what are the limitations of cross-sectional study?
- no temporal sequence (exposure and outcome measured at same time)
- can’t measure incidence or measures of association
- not good for rare exposures/outcomes
- not good for assessing transient/variable exposures or outcomes (temporary)
what type of study is an ecological study?
- descriptive and observational
what are the strengths of ecological studies?
- can asses population level exposures
- considers hypotheses
- data usually already collected so less time consuming
- less expensive
what are the limitations of ecological studies?
- doesn’t show causation
- no control for confounding
- ecological fallacy (20 year old isn’t 40)
what does a measure of association do?
it quantifies the relationship between exposre/outcome among the two groups
what does relative risk tell us?
tells us the strength of association
- how closely linked the exposure is to the outcome
what type of study is a case control study?
analytic and observational
how do case control studies work?
they work backwards
- start with participants with a known outcome status
what are the strengths of a case control study?
- good for rare outcomes and transient exposures
- can assess multiple exposures
- temporal sequencing
- quick and inexpensive compared to other studies
What are the limitations of a case control study?
- not good for multiple exposures
- difficult to select a quality control group
- susceptible to selection and recall bias
What type of study is randomised control trial?
analytic and interventional
what does RCTs measure?
similar to cohort, but instead of measuring exposure it randomises an intervention
RCT Strengths?
- calculates measures of association
- calculates incidence
- strongest design for causal association
- strongest to account for confounding and bias
RCT limitations
- expensive
- time consuming
- loss to follow up
- difficulty blinding
- non-adherance
- low generalizability
