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In cohort studies groups of people are studied over a period of time, with
certain characteristics determined at the start of the study. The cohort study
is a longitudinal study. The study follows forwards over a fixed period of time
two groups of people who have different exposures to a particular agent e.g. HRT
and non-HRT takers, but are otherwise matched. The incidence of disease is then
observed in each of the groups.
The objective of cohort studies is to test
aetiological hypotheses and estimate chronic health effects.
A cohort study
is a prospective study in contrast to a case control study which is a retrospective
In a cohort study the groups are compared with respect to disease
- HRT users -----------> incidence of breast cancer
users -----------> incidence of breast cancer
A BMJ review (1)
suggested some characteristics of cohort studies:
- populations studied
- diverse populations of patients who are observed in a range of settings
to the intervention
- based on decisions made by providers or patients
- can be defined after the intervention and can include rare or unexpected
- many cohort studies rely on existing
experience (retrospective studies) and can provide an opportunity for long follow-up
- sophisticated multivariate techniques may be
required to deal with confounding
Establish proportion with <--------- cases of DVT/PE past exposure to HRT in
- Establish proportion with <--------- no DVT/PE in
past exposure menopausal women
PA et al.Reader's guide to critical appraisal of cohort studies: 1. Role and design.
Last reviewed 06/2018