Sunday, March 29, 2015

The TES Challenge to Greg Francis

This post is a follow-up to my previous post, “Statistical alchemy and the 'test for excess significance'”. In the comments on that post, Greg Francis objected to my points about the Test for Excess Significance. I laid out a challenge in which I would use simulation to demonstrate these points. Greg Francis agreed to the details; this post is about the results of the simulations (with links to the code, etc.)

Saturday, March 28, 2015

Two things to stop saying about null hypotheses

There is a currently fashionable way of describing Bayes factors that resonates with experimental psychologists. I hear it often, particularly as a way to describe a particular use of Bayes factors. For example, one might say, “I needed to prove the null, so I used a Bayes factor,” or “Bayes factors are great because with them, you can prove the null.” I understand the motivation behind this sort of language but please: stop saying one can “prove the null” with Bayes factors.

I also often hear other people say “but the null is never true.” I'd like to explain why we should avoid saying both of these things.

Monday, March 23, 2015

BayesFactor updated to version 0.9.11-1

The BayesFactor package has been updated to version 0.9.11-1. The changes are:

  CHANGES IN BayesFactor VERSION 0.9.11-1

  * Fixed memory bug causing importance sampling to fail.

  CHANGES IN BayesFactor VERSION 0.9.11

  * Added support for prior/posterior odds and probabilities. See the new vignette for details.
  * Added approximation for t test in case of large t
  * Made some error messages clearer
  * Use callbacks at least once in all cases
  * Fix bug preventing continuous interactions from showing in regression Gibbs sampler
  * Removed unexported function oneWayAOV.Gibbs(), and related C functions, due to redundancy
  * gMap from model.matrix is now 0-indexed vector (for compatibility with C functions)
  * substantial changes to backend, to Rcpp and RcppEigen for speed
  * removed redundant struc argument from nWayAOV (use gMap instead)

Statistical alchemy and the "test for excess significance"

[This post is based largely on my 2013 article for Journal of Mathematical Psychology; see the other articles in that special issue as well for more critiques.]

When I tell people that my primary area of research is statistical methods, one of the reactions I often encounter from people untrained in statistics is that “you can prove anything with statistics.” Of course, this rankles, first because it isn't true (unless you use a very strange definition of prove) and second because I've spent years learning the limitations of statistics, and there are many limitations. These limitations exist, however, in the context of enormous successes. In the sciences, the field of statistics rightly has a place of honor.

This success is evidenced by the great number of scientific arguments that are supported by statistical methods. Not all statistical arguments are created equal, of course. But the respect with which statistics is viewed has the unfortunate downside that a statistical argument can apparently turn a leaden hunch into a golden “truth”. This post is about such statistical alchemy.

Monday, March 9, 2015

The frequentist case against the significance test, part 2

The significance test is perhaps the most used statistical procedure in the world, though has never been without its detractors. This is the second of two posts exploring Neyman's frequentist arguments against the significance test; if you have not read Part 1, you should do so before continuing (“The frequentist case against the significance test, part 1”).

The frequentist case against the significance test, part 1

It is unfortunate that today, we tend to think about statistical theory in terms of Bayesianism vs frequentism. Modern practice is a blend of Fisher's and Neyman's ideas, with the characteristics of the blend driven by convenience rather than principle. Significance tests are lumped in as a “frequentist” technique by Bayesians in an unfortunate rhetorical shorthand.

In recent years, the significance test has been critiqued on several grounds, but often these critiques are offered from Bayesian or pragmatic grounds. In a two-part post, I will outline the frequentist case developed by Jerzy Neyman against the null hypothesis significance test.

Thursday, March 5, 2015

How to shoot yourself in the foot with various statistical philosophies

I've long been a fan of "How to shoot yourself in the foot" jokes. Having shot myself in the foot with different programming languages -- particularly with C -- I was thinking about how one might shoot oneself in the foot with various statistical approaches. So, here we go...

Monday, March 2, 2015

At the APS Observer: a profile of JASP

The APS Observer has just published a profile of JASP, a graphical user interface designed to make statistics easier. It includes Bayesian procedures by means of the R and the BayesFactor package. From the article:
 JASP distinguishes itself from SPSS by being as simple, intuitive, and approachable as possible, and by making accessible some of the latest developments in Bayesian analyses. At time of writing, JASP version 0.6 implements the following analysis tools in both their classical and Bayesian manifestations:
  • Descriptive statistics
  • t tests
  • Independent samples ANOVA
  • Repeated measures ANOVA
  • Correlation
  • Linear regression
  • Contingency tables
Read more at the APS observer.

Sunday, March 1, 2015

To Beware or To Embrace The Prior

In this guest post, Jeff Rouder reacts to two recent comments skeptical of Bayesian statistics, and describes the importance of the prior in Bayesian statistics. In short: the prior gives a Bayesian model the power to predict data, and prediction is what allows the evaluation of evidence. Far from being a liability, Bayesian priors are what make Bayesian statistics useful to science.