## a new Monty Hall riddle

Posted in Books, Kids, Mountains, pictures, R, Statistics, Travel with tags , , , , , , , , , on May 22, 2020 by xi'an

The Riddler was sort of feeling the rising boredom of being under lockdown when proposing the following variant to the Monty Hall puzzle:

There are zero to three goats, with a probability ¼ each, and they are allocated to different doors uniformly among the three doors of the show. After the player chooses a door, Monty opens another door hidding a goat or signals this is impossible. Given that he did open a door, what is the probability that the player’s door does not hide a goat?

Indeed, a straightforward conditional probability computation considering all eight possible cases with the four cases corresponding to Monty opening a door leads to a probability of 3/8 for the player’s door. As confirmed by the following R code:

```s=sample
m=c(0,0)
for(t in 1:1e6)m=m+(range(s(1:3,s(1:3,1)))>1)
```

## ASC 2012 (#3, also available by mind-reading)

Posted in Running, Statistics, University life with tags , , , , , , , , , on July 13, 2012 by xi'an

This final morning at the ASC 2012 conference in Adelaide, I attended a keynote lecture by Sophia Rabe-Hesketh on GLMs that I particularly appreciated, as I am quite fond of those polymorphous and highly adaptable models (witness the rich variety of applications at the INLA conference in Trondheim last month). I then gave my talk on ABC model choice, trying to cover the three episodes in the series within the allocated 40 minutes (and got from Terry Speed the trivia information that Renfrey Potts, father to the Potts model, spent most of his life in Adelaide, where he died in 2005! Terry added that he used to run along the Torrens river, being a dedicated marathon runner. This makes Adelaide the death place of both R.A. Fisher and R. Potts.)

Later in the morning, Christl Donnelly  gave a fascinating talk on her experiences with government bodies during the BSE and foot-and-mouth epidemics in Britain in the past decades. It was followed by  a frankly puzzling [keynote Ozcots] talk delivered by Jessica Utts on the issue of parapsychology tests, i.e. the analysis of experiments testing for “psychic powers”. Nothing less. Actually, I first thought this was a pedagogical trick to capture the attention of students and debunk, however Utts’ focus on exhibiting such “powers” was definitely dead serious and she concluded that “psychic functioning appears to be a real effect”. So it came as a shock that she was truly believing in psychic paranormal abilities! I had been under the wrong impression that the 2005 Statistical Science paper of hers was demonstrating the opposite but it clearly belongs to the tradition of controversial Statistical Science that started with the Bible code paper… I also found it flabbergasting to learn that the U.S. Army is/was funding research in this area and is/was actually employing “psychics”, as well that the University of Edinburgh has a parapsychology unit within the department of psychology. (But, after all, UK universities also have long had schools of Divinity, so let the irrational in a while ago!) Continue reading