**We celebrated Jerzy Neyman’s Birthday (April 16, 1894) **last night in our seminar: here’s a pic of the cake. My entry today is a brief excerpt and a link to a paper of his that we haven’t discussed much on this blog: Neyman, J. (1962), ‘Two Breakthroughs in the Theory of Statistical Decision Making‘ [i] It’s chock full of ideas and arguments, but the one that interests me at the moment is Neyman’s conception of “his breakthrough”, in relation to a certain concept of “inference”. “In the present paper” he tells us, “the term ‘inferential theory’…will be used to describe the attempts to solve the Bayes’ problem with a reference to confidence, beliefs, etc., through some supplementation …either a substitute *a priori* distribution [exemplified by the so called principle of insufficient reason] or a new measure of uncertainty” such as Fisher’s fiducial probability. So if you hear Neyman rejecting “inferential accounts” you have to understand it in this very specific way: he’s rejecting “new measures of confidence or diffidence”. Here he alludes to them as “easy ways out”. Now Neyman always distinguishes his error statistical performance conception from Bayesian and Fiducial probabilisms [ii]. The surprising twist here is semantical and the culprit is none other than…Allan Birnbaum. Yet Birnbaum gets short shrift, and no mention is made of our favorite “breakthrough” (or did I miss it?).

Note: In this article,”attacks” on various statistical “fronts” refers to ways of attacking problems in one or another statistical research program.

**HAPPY BIRTHDAY WEEK FOR NEYMAN!**

What doesn’t Neyman like about Birnbaum’s advocacy of a Principle of Sufficiency S (p. 25)? He doesn’t like that it is advanced as a normative principle (e.g., about when evidence is or ought to be deemed equivalent) rather than a criterion that does something for you, such as control errors. (Presumably it is relevant to a type of context, say parametric inference within a model.) S is put forward as a kind of principle of rationality, rather than one with a rationale in solving some statistical problem

“The principle of sufficiency (S): If E is specified experiment, with outcomes x; if t = t (x) is any sufficient statistic; and if E’ is the experiment, derived from E, in which any outcome x of E is represented only by the corresponding value t = t (x) of the sufficient statistic; then for each x, Ev (E, x) = Ev (E’, t) where t = t (x)… (S) may be described informally as asserting the ‘irrelevance of observations independent of a sufficient statistic’.”

Ev(E, x) is a metalogical symbol referring to the evidence from experiment E with result x. The very idea that there is such a thing as an evidence function is never explained, but to Birnbaum “inferential theory” required such things. (At least that’s how he started out.) The view is very philosophical and it inherits much from logical positivism and logics of induction.The principle S, and also other principles of Birnbaum, have a normative character: Birnbaum considers them “compellingly appropriate”.

“The principles of Birnbaum appear as a kind of substitutes for known theorems” Neyman says. For example, various authors proved theorems to the general effect that the use of sufficient statistics will minimize the frequency of errors. But if you just start with the rationale (minimizing the frequency of errors, say) you wouldn’t need these”principles” from on high as it were. That’s what Neyman seems to be saying in his criticism of them in this paper. Do you agree? He has the same gripe concerning Cornfield’s conception of a default-type Bayesian account akin to Jeffreys. Why?

[i] I thank @omaclaran for reminding me of this paper on twitter in 2018.

[ii] Or so I argue in my *Statistical Inference as Severe Testing: How to Get Beyond the Statistics Wars*, 2018, CUP.

[iii] Do you think Neyman is using “breakthrough” here in reference to Savage’s description of Birnbaum’s “proof” of the (strong) Likelihood Principle? Or is it the other way round? Or neither? Please weigh in.

REFERENCES

**Neyman, J. (1962), ‘Two Breakthroughs in the Theory of Statistical Decision Making‘, Revue De l’Institut International De Statistique / Review of the International Statistical Institute, 30(1), 11-27.**