Cohort Studies Flashcards
Cohort Studies
Determines the association between exposure and disease/outcome
–start with exposure status and moves forward in time
–outcome not present in cohort at time of exposure
-Determined incidence or natural history of a disease/condition in a cohort of individuals
incidence
how many pts get disease over time
Prospective Cohort Study
-Begin in the present
-Data non-existent at time study starts
-Info about outcome is collected in the future
Retrospective Cohort Study
-begins and ends in present but involves a backward look to collect data
-Data already exists at time of study
-All relevant events (exposure and outcome) have occurred when the study is started but direction of the inquiry is still forward
Retrospective Cohort Study
-begins and ends in present but involves a backward look to collect data
-Data already exists at time of study
-All relevant events (exposure and outcome) have occurred when the study is started but direction of the inquiry is still forward
prevalence
a snapshot in time
Major difference between prospective and retrospective Cohort Studies
Whether all the data is in existence at that time the study began
When is cohort study warranted?
-when good evidence suggests an association of a disease (outcome) w/ a certain exposure(s)
-not ideal for rare diseases/outcomes
Design Issues
-Need clear definition of criteria for exposure and outcome
-Selection of exposed population
-Selection of the comparison (non-exposed) group
Biases in Cohort Studies
-Selection bias
-Information bias
-Surveillance bias
-Bias from loss to follow-up
Selection bias
assignment of exposure status is done by investigator/clinician
Information bias
Difference in quality of information obtained from exposed vs. non-exposed persons
Surveillance bias
One group followed closer and outcome-observed more frequently in that group
Bias from loss of f/u
-results may be Dif in those who had longer f/u
–more likely to develop the condition?
-Concerning if loss to f/u is >20% of cohort
Advantages of Cohort Studies
-efficient
-calculate incidence of outcome (# of newer cases over time
-Ideal when interval between exposure-outcome is short
-Established temporal relationship between exposure outcome
-Can study multiple exposures and outcomes
-Prospective-more complete data collection as investigators can dictate what data is being collected
