9.1 - Advanced Cohort Study Design

You have seen combinations of case-control design with cohort design earlier...recall:

selection of cases and a sub-cohort from the source, or original, cohort - i.e., you identify the cases from the existing cohort and select a smaller set of the cohort to follow over time as a comparison to the cases
Nested case-control
within a cohort study, cases and controls are selected for a smaller case-control investigation for example, determining case status and collecting blood or tissue samples among the cases and selected controls in a cohort; genotyping (exposure status) is done using the samples for these subjects, not the entire cohort; the association between disease and the genetic factor is assessed)

Once again, recall the comparative advantages and disadvantages of case-control and cohort studies:


  • Calculates incidence rate, risk, and relative risk
  • Potentially more strong for causal investigations
  • Expensive
  • Long-term study
  • Need large sample size
  • Good for rare exposure
  • Good for multiple outcomes
  • Less potential for recall bias
  • More potential for loss-to-followup
  • Possibly generalizable
  • Allows examination of natural course of disease, survival


  • Only an estimate of relative risk
  • Potentially less strong for causal investigation
  • Inexpensive
  • Short-term study
  • Powerful with small sample of cases
  • Good for rare disease
  • Good for multiple exposures
  • More potential for recall bias
  • Less potential for loss-to-followup
  • Probably not generalizable
  • Does not allow examination of natural course of disease, survival