cohort studies Flashcards
what is a cohort
a group with a common characteristic or experience, in a study they are followed over time after measuring their exposure status
difference between a birth and inception cohort
birth cohort all born in same time period usually a year
inception cohort all assembled on a common factor eg where they work or live
exposure and disease cohort
all share a common exposure or a group with a specific disease
basic cohort study
observational, defined group followed over time can have many follow ups
descriptive vs analytical
descriptive is hypothesis generating whereas analytical examines exposure vs outcome and uses unexposed(control) group
retrospective and prospective study
retrospective quicker cheap and outcome already occurred so no follow up
prospective slow and expensive and loss of follow up can threaten validity
open, fixed and closed study
open allows people to leave/enter
fixed is static but people can be lost and no follow up
closed fixed but assumes no loss of follow up(not good for longer studies)
special and general cohorts
special based on exposure or experience better for rare exposures
general has no idea of exposure status at the start so used for common exposures
comparison groups
in special cohorts usually external groups but in general cohorts can have internal groups (measures exposed vs unexposed)
active and passive follow ups
active is resource intensive and sometimes relies on self report
passive is limited by collected data and records
record linkage
can be deterministic(exact) or probabilistic matching
rate and risk
incident rate better when loss of follow up as it relies on person time at risk
relative risk
incident in exposed / incident in unexposed
standardised ratios
can be used when comparing against general population
some cohort study advantages
useful for rare exposures and multiple outcomes
in prospective studies exposure already defined so relationship to outcome can be clear
