value-of-information

Decide whether to buy information before a decision: a market test, pilot, survey, trial run, inspection, diagnostic, consultant report or extra data. Use whenever someone asks whether a test or study is worth its cost; the most they should pay for research, a pilot or better data; the expected value of perfect information (EVPI) or of sample information (EVSI); how an imperfect test with false positives and false negatives should update the odds; why a positive result from an accurate test can still mean the event is unlikely (base rates, Bayes' rule); or whether to decide now or wait and learn. Not for building the decision tree for a choice with no test on offer, not for A/B test sample size or significance, and not for designing the survey questionnaire itself.