POPH192- Lecture 19 Flashcards
what type of study is cohort study?
analytic and observational
what is the first step of cohort study?
- identify a source population
what is the second step in a cohort study?
- recruit the sample population who don’t have the outcome of interest
what is the third step in a cohort study?
assess their exposure level and categorise participant into appropriate group
what is the fourth step in cohort study?
follow up overtime and see who develops the outcome
what is the fifth step in cohort study?
calculate your measures of associations and occurrence
what do we know in cohort studies that we don’t know in cross-sectional or ecological study?
- that the exposure came before the outcome
how are individuals defined in cohort studies?
on the basis of presence or absence of exposure to a suspected risk factor
what calculations are used in cohort studies?
- incidence proportion
- incidence rate
- relative risk
- relative difference
what are some important things to consider in a cohort study? (5)
- the healthy worker effect
- need to be sure that the sample population doesn’t have the outcome
- need to ensure participants have been correctly classified into exposure groups
- loss to follow up (did any participants leave the study?)
- has the outcome been correctly classified?
what is the healthy worker effect?
- when studies are derived only from a population of adult workers, this cannot be generalised to he population at large.
- this is because those who are working are overall healthier than those who are not
what are the strengths of a cohort study?
- temporal sequence between exposure and outcome
- can look at multiple outcomes
- can calculate incidence, relative risk and risk difference
- good for rare exposures
what are the limitations of cohort study?
- loss to follow up and it’s associated bias
- potential for exposure/outcome misclassification
- time consuming
- expensive
- not good for rare outcomes
what are the two types of cohort studies?
- prospective
- historical
what is a prospective cohort study?
- starting when everyone is outcome free and following them up
what is historical cohort study?
start with outcome and use existing data to reconstruct the follow up (goes back in time)
what are most cohort studies?
prospective
what are historical cohort studies good for?
good for outcomes which are rare or take a long time to develop, are less expensive and less time consuming
what may cause problems in historical cohort studies?
- data quality
- selection bias
- incomplete information
what is the difference between historical cohort and case control studies?
in a case control, the investigator splits individuals by disease status whereas in retrospective (historical) cohort, the investigators splits individuals by their exposure status
