The Bayesian cringe

I used this expression the other day in Lauren’s seminar and she told me she’d never heard it before, which surprised me because I feel like I’ve been saying it for awhile, so I googled *statmodeling bayesian cringe* but nothing showed up! So I guess I should wrote it up.

Eventually everything makes its way from conversation to blog to publication. For example, the earliest appearance I can find of “Cantor’s corner” is here, but I’d been using that phrase for awhile before then, and it ultimately appeared in print (using the original Ascii art!) in this article in a physics journal.

So . . . the Bayesian cringe is this attitude that many Bayesian statisticians, including me, have had, in which we’re embarrassed to use prior information. We bend over backward to assure people that we’re estimating all our hyperparameters from the data alone, we say that Bayesian statistics is the quantification of uncertainty, and we don’t talk much about priors at all except as a mathematical construct. The priors we use are typically structural—not in the sense of “structural equation models,” but in the sense that the priors encode structure about the model rather than particular numerical values. An example is the 8 schools model—actually, everything in chapter 5 of BDA—where we use improper priors on hyperparameters and never assign any numerical or substantive prior information.

The Bayesian cringe comes from the attitude that non-Bayesian methods are the default and that we should only use Bayesian approaches when we have very good reasons—and even that isn’t considered enough sometimes, as discussed in section 3 of this article. So that’s led us to emphasize innocuous aspects of Bayesian inference. Now, don’t get me wrong, I think there are virtues to flat-prior Bayesian inference too. Not always—sometimes the maximum likelihood estimate is better, as in some multidimensional problems where the flat prior is actually very strong (see section 3 of this article) or just because it’s a mistake to take a posterior distribution too seriously if it comes from an unrealistic prior (see section 3 here)—but for the reasons given in BDA, I typically think that flat-prior Bayes is a step forward.

But I keep coming across problems where a little prior information really helps—see for example Section 5.9 here, it’s one of my favorite examples—and more and more I’ve been thinking that it makes sense to just start with a strong prior. Instead of starting with the default flat or super-weak prior, start with a strong prior (as here) and then retreat if you have prior information saying that this prior is too strong, that effects really could be huge or whatever.

As the years have gone on, I’ve become more and more sympathetic with the attitude of Dennis Lindley. As a student I’d read his contributions to discussions in statistics journals and thing, jeez what an extremist, he just says the same damn thing over and over. But now I’m like, yeah, informative priors, cut the crap, let’s go baby. As I wrote in 2009, I suspect I’d agree with Lindley on just about any issue of statistical theory and practice. I’ve read some of Lindley’s old articles and contributions to discussions and, even when he seemed like something of an extremist at the time, in retrospect he always seems to be correct.

One way we’ve moved away from the Bayesian cringe is by using the terminology of regularization. Remember how I said that lasso (and, more recently, deep nets) have made the world safe for regularization? And how I said that Bayesian inference is not radical but conservative (sorry, Lindley)? When we talk about regularization, we’re saying that this kind of partial-pooling-toward-the-prior is desirable in itself. Rather than being a regrettable concession to bias that we accept in order to control our mean squared error, we argue that stability is a goal in itself. (Conservative, you see?)

We’re not completely over the Bayesian cringe—look at just about any regression published in a political science journal, and within econometrics there are still some old-school firebreathers of the anti-Bayesian type—but I think we’re gradually moving toward a general idea that it’s best to use all available information, with informative priors being one way to induce stability and thus allow us to fit more complicated, realistic, and better-predicting models.

21 thoughts on “The Bayesian cringe

  1. In statistics in general, there seems have been a long term attitude that assumptions are just a necessary price to pay to do the analysis, develop methods and admittedly launder a lot of model uncertainty.

    For a scientific perspective assumptions should be recognized as purposeful attempts to represent aspects of reality or supplement such representations (i.e. priors for nuisance parameters). This includes checking the prior and data generating assumptions as a way to make them less wrong (better connected with reality) and evaluate critical roles of each.

    Reminds of Freud admitting that psychology was not yet scientific, but he did not want to change careers. This, I can’t justify the priors I am using but I want to do a Bayesian analysis anyway. Or as someone once put, pull the Bayesian crank and claim to have solved all the analysis problems.

    On the other hand there is a simple mitigation. If one is not sure of justifications of the prior, in most cases, a frequency calibration can be carried out using simulation. This discloses any possible increases in frequency risks that one might be taking by not doing a frequency analysis. Often that will be acceptable.

    Refusing to do that as one feels frequency properties make no sense, is like someone refusing to disclose possible conflict of interest as they don’t think it is conflict. Let the end users (collaborators, audience, etc.) evaluate this on their own.

    Maybe this refusal should be called “Bayesian ostrich-ing”

  2. The Cringe will persist as long as significance testing is the dominant research paradigm. If we don’t care about significance testing, then priors become interesting topics of legitimate, reasonable discussion.

  3. One of his best writings are in the Valencia Proceedings (incl. “Is our View of Bayesian Statistics Too Narrow?”). Alas they are near impossible to find these days (and the copies on Amazon charge you an arm and a leg).

  4. The posterior inherits meaning from the prior. If the prior has no meaning, neither has the posterior.
    As a pluralist with some frequentist leanings, I like to see Bayesian analyses with a well motivated prior where the authors manage to convince me that the prior is used to involve some useful information that otherwise would have been ignored. Sadly the majority of Bayesian papers that I see don’t bother to motivate the prior in any depth (sometimes convenience is used as the only argument, which is better than not having any, as I also often see; what I also often see is that prior and hyperprior involve a number of choices and out of say six choices one is motivated from some prior information), which doesn’t make me feel that anything is won by doing this the Bayesian way.

    De Finetti by the way wrote (from my memory, which isn’t all too reliable) that there always is some information, and one should really make the effort to bring it out, therefore he isn’t really interested in “informationless priors”.

  5. Jacob Feldman talks about this topic in his paper “Tuning your Priors to the World” (https://pubmed.ncbi.nlm.nih.gov/23335572/)

    From the abstract: “Whenever there is uncertainty about the environment—which there almost always is—an agent’s prior should be biased away from ecological relative frequencies and toward simpler and more entropic priors.”

    I wish Feldman would write more about this stuff!

  6. I only cringe when Bayesians claim sovereignty over the idea of quantifying uncertainty (present company excluded, of course!). Some frequentists care a lot about uncertainty and are perfectly capable of quantifying it rigorously.

    • Capable sure, but rarely willing when it comes to teaching statistics, in my experience. Perhaps the immense damage NHST has wrecked on the integrity of statistical analysis is ultimately Fisher’s fault, but every frequentist STAT 101/201/301 prof who continues to teach the self-contradictory, unphysical NHST paradigm to trusting social & physical science undergraduates deserves the snootiness from Bayesians–the metaphorical blood of the replication crisis is ultimately on their (and Fisher’s and Feller’s and …) hands.

  7. > I suspect I’d agree with Lindley on just about any issue of statistical theory and practice

    I think he was somewhat less sympathetic to the notion of “empirical Bayes”. [there is no one less Bayesian than an empirical Bayesian]

    • Dennis Linley visited our department in 1978 while I was a PhD student there. My PhD supervisor John Deely had published in the Empirical literature and had challenged Lindley to explain he reasons behind his statement “there is no one less Bayesian than an empirical Bayesian”. he result was their joint article in JASA “Bayes Empirical Bayes” (December 1981 avaiable on JSTOR).

      • Sorry for the misspelling and typo – “Dennis Lindley visited our department in 1978 while I was a PhD student there. My PhD supervisor John Deely had published in the Empirical Bayes literature ….”

  8. Somewhat off topic, but does anyone know a reasonably natural example of an iterated Simpson’s paradox, where you can divide once to reverse the correlation, and then divide again to get back the original one?

  9. > Lindley was right.
    Well this was his last talk – https://xianblog.wordpress.com/2013/08/20/dennis-lindley-and-tony-ohagan-on-youtube/

    Now to me, an axiom system that he envisions for statistics is just deduction and although deduction is part of statistics (trying to learn about the empirical world) most of statistics has to be induction.

    That is the reason why the premises (prior, data generating model and data) need to be critically assess/checked and performance of miss-specified models (premises) some how assessed which motivated my comment above – https://statmodeling.stat.columbia.edu/2021/09/15/the-bayesian-cringe/#comment-2023368

    • >most of statistics has to be induction.

      Premises are inherently deductive if you consider the body of research that came before. The interpretation of models, however, is inductive and if one finds out that the premises don’t hold then this might also call for inductive reasoning. I can’t see any contradiction.

      • Deduction just involves the discernment of what is contained in the premises – their implications.

        Not all sure what mean by “Premises are inherently deductive”. Perhaps the body of research that came before is abstracted into a model using abduction and induction? Then we are back to deduction from that (always wrong) model…

  10. In almost all the work that we do nowadays in my lab, we just “buy the entire market”: we always do a sensitivity analysis, using a range of priors going from mildly (un)informative to informative. It seems reasonable to report a range of posteriors under different priors. Usually, the target parameter is rock steady under different priors.

    In one case only, I have fit models with three radically different priors, following a methodology spelt out in one of Spiegelhalter’s books: an agnostic prior, an enthusiastic prior (informative–based on my own model’s a priori predictions), and an adversarial (the opponent’s informative) prior. The posterior looks very different under the enthusiastic and adversarial priors (which are the interesting cases). What I like is that I can formally encapsulate the scientific disagreement within the statistical models themselves. I will never convince through data that my scientific opponents that their belief is wrong, because their priors are so tight. The data don’t really matter much if you already think you know the truth, which is a common disease in linguistics.

    I have come to the conclusion that Chomsky and his acolytes are actually right to ignore experimental data and just rely on intuition—what linguists do is prior self-elicitation, and then base their arguments on their own prior predictive distributions of the “facts”. In linguistics, what happens most often is that the data only end up sullying the priors.

  11. I think I understand the “Bayesian Cringe.” However, I do not and never will suffer from it. The reason that I won’t relates to how I became a self-aware Bayesian (everybody is really a Bayesian for important decisions in their own lives—whether they know it or not).

    I was exposed to Bayesian inference by two independent sources. First, as those have seen my earlier posts probably know, I am a communications engineer. For decades communications engineering has used tools based on Bayesian concepts to build systems. For example, literally billions of devices have been built (cellphones, digital TVs, CD/DVD players) that include a Bayesian processor. Specifically, the Viterbi Algorithm—often characterized as an example of a Bayesian belief propagation network—has been implemented in hardware billions of times.

    Understanding and using the Viterbi Algorithm does not require one to be a Bayesian—but it does require one to accept Bayesian reasoning at each step along the trellis. There are many other examples of the use of Bayesian reasoning in communications engineering.

    Cell phones work. Bayesian inference works. And, in my experience, using Bayesian reasoning and terminology in the communications engineering workplace is unexceptional. If you look at one of the earliest textbooks setting forth the statistical theory of communications engineering (Davenport and Root, 1958), you will find an exposition of the Bayesian approach to hypothesis testing together with cost functions for the types of errors. In summarizing the Bayesian approach, the authors state “There is often difficulty in applying it [Bayesian tests] first because of difficult in assigning losses, second because of difficulty of assigning a priori probabilities.” Later, in discussing hypothesis testing, the authors state “The likelihood principle can be untrustworthy in certain applications. Obviously, if the observer uses a likelihood-ratio test when there is actually a probability distribution on Ω of which he is unaware, he may get a test which differs radically from the test for minimum probability of error.” That’s an endorsement of the Bayesian approach.

    My second, completely independent, exposure to Bayesian reasoning was through the statistical decision theory of Pratt, Raiffa, and Schlaifer. I was exposed to it via some social contacts and I also took a course on it from a professor who I think was one of Raiffa’s PhD advisees. In the decision making world, Bayesian reasoning seems somewhere between natural and unassailably necessary.

    I also took a course in frequentist statistics. It never really took. I should point out that the incorporation of the methods of frequentist statistics into communications engineering, which occurred in the 1940s and 50s, advanced the art and proved to be extremely useful.

    My point is that my exposure to formal Bayesian methods was in contexts where it seems to me that they were/are incontrovertibly correct.

    The most compelling criticism of Bayesian statistics that I recall (from many year ago) was that it was too hard—too computationally difficult—to apply for everyday statistical problems. Well, with the techniques and computers of the 1970s it was too difficult. It appears to me (from reading this blog) that is no longer the case.

    So, a “Bayesian Cringe” is justified only in those instances where one knows that the Bayesian tools have a significant probability of not working.

    Bob76
    PS. Maybe there is something in the water at Berkeley that induces a distaste for Bayesian thought.

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