**T**hird day at MCMskv, where I took advantage of the gap left by the elimination of the Tweedie Race [second time in a row!] to complete and submit our mixture paper. Despite the nice weather. The rest of the day was quite busy with David Dunson giving a plenary talk on various approaches to approximate MCMC solutions, with a broad overview of the potential methods and of the need for better solutions. (On a personal basis, great line from David: “five minutes or four minutes?”. It almost beat David’s question on the previous day, about the weight of a finch that sounded suspiciously close to the question about the air-speed velocity of an unladen swallow. I was quite surprised the speaker did not reply with the Arthurian “An African or an European finch?”) In particular, I appreciated the notion that some problems were calling for a reduction in the number of parameters, rather than the number of observations. At which point I wrote down “multiscale approximations required” in my black pad, a requirement David made a few minutes later. (The talk conditions were also much better than during Michael’s talk, in that the man standing between the screen and myself was David rather than the cameraman! Joke apart, it did not really prevent me from reading them, except for most of the jokes in small prints!)

The first session of the morning involved a talk by Marc Suchard, who used continued fractions to find a closed form likelihood for the SIR epidemiology model (I love continued fractions!), and a talk by Donatello Telesca who studied non-local priors to build a regression tree. While I am somewhat skeptical about non-local testing priors, I found this approach to the construction of a tree quite interesting! In the afternoon, I obviously went to the intractable likelihood session, with talks by Chris Oates on a control variate method for doubly intractable models, Brenda Vo on mixing sequential ABC with Bayesian bootstrap, and Gael Martin on our consistency paper. I was not aware of the Bayesian bootstrap proposal and need to read through the paper, as I fail to see the appeal of the bootstrap part! I later attended a session on exact Monte Carlo methods that was pleasantly homogeneous. With talks by Paul Jenkins (Warwick) on the exact simulation of the Wright-Fisher diffusion, Anthony Lee (Warwick) on designing perfect samplers for chains with atoms, Chang-han Rhee and Sebastian Vollmer on extensions of the Glynn-Rhee debiasing technique I previously discussed on the blog. (Once again, I regretted having to make a choice between the parallel sessions!)

The poster session (after a quick home-made pasta dish with an exceptional Valpolicella!) was almost universally great and with just the right number of posters to go around all of them in the allotted time. With in particular the Breaking News! posters of Giacomo Zanella (Warwick), Beka Steorts and Alexander Terenin. A high quality session that made me regret not touring the previous one due to my own poster presentation.