## The Standard Bayesian-Frequentist Debate About Stopping Rules

**Bayesians generally reject the frequentist view that inference and decision procedures should be sensitive to differences among “stopping rules”**—that is, the (possibly implicit) processes by which experimenters decide when to stop collecting the data that will be fed into those procedures—outside of unusual cases in which the stopping rule is “informative” in a technical sense.

Frequentists often argue for their position by claiming that **ignoring differences among noninformative stopping rules would allow experimenters to produce systematically misleading results**. For instance, Mayo and Kruse (2001) consider the case of a subject who claims to be able to predict draws from a deck of ESP cards. On a frequentist approach, if a 5% significance level is used and the data are treated as if the sample size had been fixed in advance, then the probability of rejecting the “null hypothesis” that the subject has no extrasensory abilities within the first 1000 observations if that hypothesis is true is 53%, and the probability of rejecting it within some finite number of observations is one. Accordingly, Mayo and Kruse claim that whether the experimenter had planned to stop after 1000 trials all along or had planned to stop as soon as a statistically significant outcome had occurred must be reported and must be taken into account in inference and decision. [Read more…]