## Typo in Bayesian Core [again]

**R**eza Seirafi from Virginia Tech sent me the following email about * Bayesian Core*, which alas is pointing out a real typo in the reversible jump acceptance probability for the mixture model:

With respect to the expression provided on page 178 for the acceptance probability of the split move, I was wondering if the omission of the density of the auxiliary parameters u

_{1}, u_{2}, and u_{3}— specially u_{2}, since its density is not necessarily equal to 1 contrary to the other two — is a case of typo.

**T**his is truly a typo, the acceptance probability at the bottom of page 178 should be

since *u _{2}* is indeed distributed from a non-uniform density. The physical reason for this (unacceptable!) typo is that I cut-and-pasted the LaTeX code from

*: (page 439) where*

**Monte Carlo Statistical Methods***u*is a uniform variate! (Incidentally, there is a minor typo a few lines above: when defining

_{2},

it should be

,

another side casualty of cut-and-paste!) Obviously, this could also affect the associated R code but I checked it and found the line

jacob=(kprop-2)*log(1-propp[kprop]) - singleprior(propmix,kprop)

which I think is correcting for the normal proposal.

**T**his typo will obviously be corrected in the next printing of* Bayesian Core* as well as in the new edition we plan to write in July. It also illustrates the folk theorem “

*One can never write the reversible jump acceptance probability right*” that make me avoid using reversible jump each time I am facing a small enough collection of models to consider the exhaustive list of those models.

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