Chapter 8

External Validity, Generalizability, and Transportability

4 videos · about 35 minutes · watch as a YouTube playlist →

  1. 1External validity, generalizability, and transportabilityClinical Trial 320 showed that three-drug combination therapy cut the risk of AIDS or death roughly in half; re-analyzed years later for a different population, the estimated benefit shrank. External validity as the umbrella, with generalizability and transportability underneath it.5 min
  2. 2Does the sample stand for the population it came from?Generalizability asks whether results from your sample stand for the population that sample came from, worked four times: an estimate carried by its sampling design, one carried by a model’s assumptions, findings honest about belonging to one village, and a causal effect whose reach depends on effect modification.10 min
  3. 3Do the results apply to a different population entirely?Transportability asks whether results apply to a population your sample was never part of, and no amount of better sampling fixes it. A 1997 HIV trial carried to a later population by re-expressing its age-specific effects against that population’s composition.10 min
  4. 4Designing for external validityExternal validity as a design decision made before enrollment rather than an analysis run afterward, then Shadish, Cook and Campbell’s five threats as a checklist you can put to your own design or to someone else’s paper.10 min

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