AS2: Wk 7, Cohort Studies

AS2: Wk 7, Cohort Studies

1. Risk Ratio

   • The probability of an event occurring in the exposed group to the probability of an event occurring in the non-exposed group
   • Divide the RR of the exposd group by the RR of the non-exposed group
     • (A/ A + B) / (C/ C + D)

2. Groups categorised based on exposure

3. Usually prospective

4. Can be retrospective

   • Lose study subjects due to recall bias

5. Cumulative Incidence (CI)

   • The probability of an animal becoming a case in a given time frame
   • No. of cases in time period/ total no. of animals in the study
   • Affected by the length of the study (i.e. the longer a group of animals is observed, the more likely they are to become diseased

6. Incidence Ratio (IR)

   • Takes TIME into account
   • Animal days at risk
     • No. of animals in study X no. of days at risk
   • No. of cases X animal days at risk