Cohort studies

Cohort studies

1. Prospective / forward directionality

   • Fixed cohort
     • Group identified at the onset
   • Non-fixed cohort
     • Subjects progessively added over time
   • The choice of disease measures and effect are influenced by the design
   • Timing can be either prospective or retrospective

2. features

   • participants are grouped before the study dependant on their exposure
   • analysis by actual experience

3. Advantages

   • proesctive
     • less prone to obtaining incorrect information
   • free of most selection bias
   • retrospective
     • good for rare exposures
     • are low cost and quick

4. Disadvantages

   • prospective
     • loss of subjects
       • leads to bias
     • not good for rare disease
     • are costly and time consuming
   • exposed may be followed more closely than unexposed
     • incorrect relationship found?

5. measures of association by RELATIVE RISK