Cohort Studies Flashcards
What are the limitations of cohort studies?
Large and resource intensive, takes a long time (concurrent studies), rigorous definitions of exposure & disease can require expensive/invasive investigation, high drop out rate in follow up leads to survivor bias (those left are more likely to do as told and therefore live healthily), not good for rare diseases - too few cases, confounding factors.
What are the benefits of cohort studies?
Can study rare/unusual exposure, can obtain more detail information on exposures and outcomes, can get additional data on potential confounding factors, can study a range of outcomes, good for conditions which fluctuate with age (lexis plot).
What is an internal comparison?
Comparison of incidence rates between sub cohorts (IRR).
What is an external comparison?
Calculate SMR of cohort using a reference population.
What are the limitations of an external comparison?
Data available is often limited for reference populations, may have to use mortality data instead of incidence. May encounter selection bias (eg. healthy worker effect).
What is a limitation of internal cohort comparison?
If one cohort has a low incidence it means there will be a high error factor.
How is a concurrent/prospective cohort study conducted?
Pick disease free individuals and classify them accordingly to their exposure and start collecting data immediately or after a period of time (could be a few years if no outcome expected before then).
How is a historical/retrospective cohort study conducted?
Pick disease free individuals from a certain point in time, classify their initial exposure and follow up using historical records.
