prior probability

We have had to sit through a countless number of mind-numbing social science presentations and empirical papers during our academic career, most or all of which have relied on standard frequentist methods. We are writing today to request a favor. Why can’t we just admit that subjective priors are unavoidable in any field of inquiry? After all, we must necessarily begin with our priors when deciding what set of problems to solve and how to solve them. Why pretend otherwise? (By the way, all of you are smart people. Many of you have PhD’s and have many years of book learning and practical experience in your various fields. If any group of individuals is likely to have well-informed priors or good hunches about well-defined research problems, it’s you!)

Many of our colleagues, however, continue to reject Bayesian methods. You cling to an idealized conception of science. You equate “science” with standard frequentist methods, that is, with the ad hoc and easily manipulable statistical methods of Fisher, Pearson, and others. But this view of science is too narrow, too static. Science is ultimately about discovery, not about p values. Furthermore, all knowledge is contingent, including scientific or experimental knowledge. Nothing is certain. Thus the Bayesian notion of “degrees of belief” provides a realistic understanding of how our knowledge actually evolves over time. To discover, one must be willing to update one’s priors (whatever their source or level of subjectivity) in light of new evidence. Bayesian updating is an ongoing and never-ending process.

Where have we gone wrong?

Yours truly,

Prior Probability