## Archive for þ

## Þe Norse farce [design #2]

Posted in Kids, Mountains, pictures with tags Þe Norse face, þ, design, helmet, parody, Scandinavia, thor, Viking helmet, ye Norse farce on November 19, 2018 by xi'an## intrinsic quantity for a Markov chain?

Posted in Statistics with tags þ, bootstrap, convergence assessment, CREST, effective sample size, Gainesville, Markov chain Monte Carlo, renewal process on February 6, 2013 by xi'an**I** was attending a lecture this morning at CREST by Patrice Bertail where he was using estimated renewal parameters on a Markov chain to build (asymptotically) convergent bootstrap procedures. Estimating renewal parameters is obviously of interest in MCMC algorithms as they can be used to assess the convergence of the associated Markov chain: That is, if the estimation does not induce a significant bias. Another question that came to me during the talk is that; since those convergence assessments techniques are formally holding for any small set, choosing the small set in order to maximise the renewal rate also maximises the number of renewal events and hence the number of terms in the control sequence: Thus, the maximal renewal rate þ is definitely a quantity of interest: Now, is this quantity þ an intrinsic parameter of the chain, i.e. a quantity that drives its mixing and/or converging behaviour(s)? For instance; an iid sequence has a renewal rate of 1; because the whole set is a “small” set. Informally, the time between two consecutive renewal events is akin to the time between two simulations from the target and stationary distribution, according to the Kac’s representation we used in our AAP paper with Jim Hobert. So it could be that þ is directly related with the effective sample size of the chain, hence the autocorrelation. *(A quick web search did not produce anything relevant:)* Too bad this question did not pop up last week when I had the opportunity to discuss it with Sean Meyn in Gainesville!