Monday, May 29, 2017

New version of BEST package (Bayesian estimation of two groups)

Mike Meredith has updated the BEST package again! 

CHANGES in v.0.5.0 (2017-05-28)

  * 'BESTmcmc' uses 'rjags' directly, instead of 'jagsUI' wrappers. This resolves 'set.seed' issues, but values returned will not be the same as with previous versions.

  * Function 'hdi' removed; imports HDInterval::hdi instead.

Mike created and updates the BEST package entirely on his own. He has implemented some wonderful functionality and protections in the BEST package that are not in the original R code I created to accompany the BEST article. Thanks Mike!

Reminders of some recent posts:

Thursday, May 25, 2017

Looking for great teachers of Bayesian statistics

I'm looking for great teachers of Bayesian statistics!
  • Have you taught a course in Bayesian statistics? 
  • Have you used DBDA2E
  • Are you an enthusiastic teacher with very high evaluations?
  • Do you have an abiding interest in a range of applied statistical methods?
If so, please send me an email ( Even if you think I should already know about you, please send me an email now so I can be sure to put you on the list. If you know of someone else who has those qualities -- maybe a colleague, or maybe a teacher in a class you've taken -- please tell me about that person.


P.S. This applies to instructors anywhere on the planet; just need to be fluent in English for teaching.

Thursday, May 4, 2017

Bent Coins for a Twisted Mind

Ben Motz voluntarily sat through an entire semester of my Bayesian stats course. In karmic retribution, after the conclusion of the course he surprised me with a set of biased coins that he designed and created with the amazing craftsmanship of Jesse Goode. Obverse and reverse:

Heads: In Bayes Rule We Trust!

Tails: Wagging at a (posterior) beta distribution
parameterized by mode and concentration.
(And notice the half-folded ears.)

Ben was intrigued by claims [see footnote 2, p. 73, of DBDA2E] that normal coins when flipped cannot be biased (unlike normal coins when spun), but bent coins when flipped can be biased. Ever the empiricist, he decided to conduct an experiment using progressively bent coins (while manifestly expressing his teacher evaluation at the same time).

A set of progressively bent coins!

Each coin was flipped 100 times, letting it land on a soft mat. The results are shown below:
Data from flipping each coin 100 times. Prior was beta(1,1).

Clearly the most acutely bent coins do not come up heads half the time. One paradoxical thing I like about a bent coin is that the less you can see of its face, the more its face comes up!

To preserve the apparatus of this classic experiment for posterity, and especially to give me something for show-and-tell at the old Bayesians' home, Jesse built a beautiful display box:

Protected by plexiglass from the thronging crowds of onlookers.

How did they manufacture these coins? It was quite a process. Starting with discs of metal, Jesse powder coated and baked them to get a smooth and secure coating. Then he used a computerized laser to burn off areas of the coating to reveal the shiny metal as background to the design. Finally, they used psychic telekenesis to bend the coins. (Ben assured me, however, that he withheld psychokenesis when flipping the coins.)

I've gotta admit this made my day, and it makes me smile and laugh even as I type this. I hope it gives you a smile too! Huge thanks to Ben Motz and Jesse Goode.