Markus Ojala writes: Bayesian modeling is becoming mainstream in many application areas. Applying it needs still a lot of knowledge about distributions and modeling techniques but the recent development in probabilistic programming languages have made it much more tractable. Stan is a promising language that suits single analysis cases well. With the improvements in approximation […]

**Statistical computing**category.

## We were measuring the speed of Stan incorrectly—it’s faster than we thought in some cases due to antithetical sampling

Aki points out that in cases of antithetical sampling, our effective sample size calculations were unduly truncated above at the number of iterations. It turns out the effective sample size can be greater than the number of iterations if the draws are anticorrelated. And all we really care about for speed is effective sample size […]

## Static sensitivity analysis: Computing robustness of Bayesian inferences to the choice of hyperparameters

Ryan Giordano wrote: Last year at StanCon we talked about how you can differentiate under the integral to automatically calculate quantitative hyperparameter robustness for Bayesian posteriors. Since then, I’ve packaged the idea up into an R library that plays nice with Stan. You can install it from this github repo. I’m sure you’ll be pretty […]

## Three new domain-specific (embedded) languages with a Stan backend

One is an accident. Two is a coincidence. Three is a pattern. Perhaps it’s no coincidence that there are three new interfaces that use Stan’s C++ implementation of adaptive Hamiltonian Monte Carlo (currently an updated version of the no-U-turn sampler). ScalaStan embeds a Stan-like language in Scala. It’s a Scala package largely (if not entirely […]

## “Each computer run would last 1,000-2,000 hours, and, because we didn’t really trust a program that ran so long, we ran it twice, and it verified that the results matched. I’m not sure I ever was present when a run finished.”

Bill Harris writes: Skimming Michael Betancourt’s history of MCMC [discussed yesterday in this space] made me think: my first computer job was as a nighttime computer operator on the old Rice (R1) Computer, where I was one of several students who ran Monte Carlo programs written by (the very good) chemistry prof Dr. Zevi Salsburg […]

## How does probabilistic computation differ in physics and statistics?

[image of Schrodinger’s cat, of course] Stan collaborator Michael Betancourt wrote an article, “The Convergence of Markov chain Monte Carlo Methods: From the Metropolis method to Hamiltonian Monte Carlo,” discussing how various ideas of computational probability moved from physics to statistics. Three things I wanted to add to Betancourt’s story: 1. My paper with Rubin […]

## R-squared for Bayesian regression models

Ben, Jonah, Imad, and I write: The usual definition of R-squared (variance of the predicted values divided by the variance of the data) has a problem for Bayesian fits, as the numerator can be larger than the denominator. We propose an alternative definition similar to one that has appeared in the survival analysis literature: the […]

## Burn-in for MCMC, why we prefer the term warm-up

Here’s what we say on p.282 of BDA3: In the simulation literature (including earlier editions of this book), the warm-up period is called burn-in, a term we now avoid because we feel it draws a misleading analogy to industrial processes in which products are stressed in order to reveal defects. We prefer the term ‘warm-up’ […]

## Workflow, baby, workflow

Bob Carpenter writes: Here’s what we do and what we recommend everyone else do: 1. code the model as straightforwardly as possible 2. generate fake data 3. make sure the program properly codes the model 4. run the program on real data 5. *If* the model is too slow, optimize *one step at a time* […]

## Interactive visualizations of sampling and GP regression

You really don’t want to miss Chi Feng‘s absolutely wonderful interactive demos. (1) Markov chain Monte Carlo sampling I believe this is exactly what Andrew was asking for a few Stan meetings ago: Chi Feng’s Interactive MCMC Sampling Visualizer This tool lets you explore a range of sampling algorithms including random-walk Metropolis, Hamiltonian Monte Carlo, […]

## Bin Yu and Karl Kumbier: “Artificial Intelligence and Statistics”

Yu and Kumbier write: Artificial intelligence (AI) is intrinsically data-driven. It calls for the application of statistical concepts through human-machine collaboration during generation of data, development of algo- rithms, and evaluation of results. This paper discusses how such human-machine collaboration can be approached through the statistical concepts of population, question of interest, representativeness of training […]

## How not to compare the speed of Stan to something else

Someone’s wrong on the internet And I have to do something about it. Following on from Dan’s post on Barry Gibb statistical model evaluation, here’s an example inspired by a paper I found on Google Scholar searching for Stan citations. The paper (which there is no point in citing) concluded that JAGS was faster than […]

## Computational and statistical issues with uniform interval priors

There are two anti-patterns* for prior specification in Stan programs that can be sourced directly to idioms developed for BUGS. One is the diffuse gamma priors that Andrew’s already written about at length. The second is interval-based priors. Which brings us to today’s post. Interval priors An interval prior is something like this in Stan […]

## Using output from a fitted machine learning algorithm as a predictor in a statistical model

Fred Gruber writes: I attended your talk at Harvard where, regarding the question on how to deal with complex models (trees, neural networks, etc) you mentioned the idea of taking the output of these models and fitting a multilevel regression model. Is there a paper you could refer me to where I can read about […]

## Stan is a probabilistic programming language

See here: Stan: A Probabilistic Programming Language. Journal of Statistical Software. (Bob Carpenter, Andrew Gelman, Matthew D. Hoffman, Daniel Lee, Ben Goodrich, Michael Betancourt, Marcus Brubaker, Jiqiang Guo, Peter Li, Allen Riddell) And here: Stan is Turing Complete. So what? (Bob Carpenter) And, the pre-stan version: Fully Bayesian computing. (Jouni Kerman and Andrew Gelman) Apparently […]

## Computing marginal likelihoods in Stan, from Quentin Gronau and E. J. Wagenmakers

Gronau and Wagemakers write: The bridgesampling package facilitates the computation of the marginal likelihood for a wide range of different statistical models. For models implemented in Stan (such that the constants are retained), executing the code bridge_sampler(stanfit) automatically produces an estimate of the marginal likelihood. Full story is at the link.

## In the open-source software world, bug reports are welcome. In the science publication world, bug reports are resisted, opposed, buried.

Mark Tuttle writes: If/when the spirit moves you, you should contrast the success of the open software movement with the challenge of published research. In the former case, discovery of bugs, or of better ways of doing things, is almost always WELCOMED. In some cases, submitters of bug reports, patches, suggestions, etc. get “merit badges” […]

## The network of models and Bayesian workflow

This is important, it’s been something I’ve been thinking about for decades, it just came up in an email I wrote, and it’s refreshingly unrelated to recent topics of blog discussion, so I decided to just post it right now out of sequence (next slot on the queue is in May 2018). Right now, standard […]

## Barry Gibb came fourth in a Barry Gibb look alike contest

Every day a little death, in the parlour, in the bed. In the lips and in the eyes. In the curtains in the silver, in the buttons, in the bread, in the murmurs, in the gestures, in the pauses, in the sighs. – Sondheim The most horrible sound in the world is that of a […]

## Workshop on Interpretable Machine Learning

Andrew Gordon Wilson sends along this conference announcement: NIPS 2017 Symposium Interpretable Machine Learning Long Beach, California, USA December 7, 2017 Call for Papers: We invite researchers to submit their recent work on interpretable machine learning from a wide range of approaches, including (1) methods that are designed to be more interpretable from the start, […]