Stephen Kissler and Yonatan Grad launched a Shiny app, Effective SARS-CoV-2 test sensitivity, to help you answer the question, How many infectious people are likely to show up to an event, given a screening test administered n days prior to the event? Here’s a screenshot. The app is based on some modeling they did with […]

**R**

## Probabilities for action and resistance in Blades in the Dark

Later this week, I’m going to be GM-ing my first session of Blades in the Dark, a role-playing game designed by John Harper. We’ve already assembled a crew of scoundrels in Session 0 and set the first score. Unlike most of the other games I’ve run, I’ve never played Blades in the Dark, I’ve only […]

## Drunk-under-the-lamppost testing

Edit: Glancing over this again, it struck me that the title may be interpreted as being mean. Sorry about that. It wasn’t my intent. I was trying to be constructive and I really like that analogy. The original post is mostly reasonable other than on this one point that I thought was important to call […]

## Make Andrew happy with one simple ggplot trick

By default, ggplot expands the space above and below the x-axis (and to the left and right of the y-axis). Andrew has made it pretty clear that he thinks the x axis should be drawn at y = 0. To remove the extra space around the axes when you have continuous (not discrete or log […]

## Naming conventions for variables, functions, etc.

The golden rule of code layout is that code should be written to be readable. And that means readable by others, including you in the future. Three principles of naming follow: 1. Names should mean something. 2. Names should be as short as possible. 3. Use your judgement to balance (1) and (2). The third […]

## Beautiful paper on HMMs and derivatives

I’ve been talking to Michael Betancourt and Charles Margossian about implementing analytic derivatives for HMMs in Stan to reduce memory overhead and increase speed. For now, one has to implement the forward algorithm in the Stan program and let Stan autodiff through it. I worked out the adjoint method (aka reverse-mode autodiff) derivatives of the […]

## Econometrics postdoc and computational statistics postdoc openings here in the Stan group at Columbia

Andrew and I are looking to hire two postdocs to join the Stan group at Columbia starting January 2020. I want to emphasize that these are postdoc positions, not programmer positions. So while each position has a practical focus, our broader goal is to carry out high-impact, practical research that pushes the frontier of what’s […]

## Non-randomly missing data is hard, or why weights won’t solve your survey problems and you need to think generatively

Throw this onto the big pile of stats problems that are a lot more subtle than they seem at first glance. This all started when Lauren pointed me at the post Another way to see why mixed models in survey data are hard on Thomas Lumley’s blog. Part of the problem is all the jargon […]

## Seeking postdoc (or contractor) for next generation Stan language research and development

The Stan group at Columbia is looking to hire a postdoc* to work on the next generation compiler for the Stan open-source probabilistic programming language. Ideally, a candidate will bring language development experience and also have research interests in a related field such as programming languages, applied statistics, numerical analysis, or statistical computation. The language […]

## (Markov chain) Monte Carlo doesn’t “explore the posterior”

[Edit: (1) There’s nothing dependent on Markov chain—the argument applies to any Monte Carlo method in high dimensions. (2) No, (MC)MC is not not broken.] First some background, then the bad news, and finally the good news. Spoiler alert: The bad news is that exploring the posterior is intractable; the good news is that we […]

## NYC Meetup Thursday: Under the hood: Stan’s library, language, and algorithms

I (Bob, not Andrew!) will be doing a meetup talk this coming Thursday in New York City. Here’s the link with registration and location and time details (summary: pizza unboxing at 6:30 pm in SoHo): Bayesian Data Analysis Meetup: Under the hood: Stan’s library, language, and algorithms After summarizing what Stan does, this talk will […]

## StanCon Helsinki streaming live now (and tomorrow)

We’re streaming live right now! Thursday 08:45-17:30: YouTube Link Friday 09:00-17:00: YouTube Link Timezone is Eastern European Summer Time (EEST) +0300 UTC Here’s a link to the full program [link fixed]. There have already been some great talks and they’ll all be posted with slides and runnable source code after the conference on the Stan […]

## Thanks, NVIDIA

Andrew and I both received a note like this from NVIDIA: We have reviewed your NVIDIA GPU Grant Request and are happy support your work with the donation of (1) Titan Xp to support your research. Thanks! In case other people are interested, NVIDA’s GPU grant program provides ways for faculty or research scientists to […]

## Where do I learn about log_sum_exp, log1p, lccdf, and other numerical analysis tricks?

Richard McElreath inquires: I was helping a colleague recently fix his MATLAB code by using log_sum_exp and log1m tricks. The natural question he had was, “where do you learn this stuff?” I checked Numerical Recipes, but the statistical parts are actually pretty thin (at least in my 1994 edition). Do you know of any books/papers […]

## The current state of the Stan ecosystem in R

(This post is by Jonah) Last week I postedÂ here about the release of version 2.0.0 of the loo R package, butÂ there have been a few other recent releases and updates worth mentioning. At the end of the post I also include some general thoughts on R package development with Stan and the growing number of […]

## loo 2.0 is loose

This post is by Jonah and Aki. We’re happy to announce the release of v2.0.0 of the loo R package for efficient approximate leave-one-out cross-validation (and more). For anyone unfamiliar with the package, the original motivation for its development is in our paper: Vehtari, A., Gelman, A., and Gabry, J. (2017). Practical Bayesian model evaluation […]

## 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 […]

## StanCon is next week, Jan 10-12, 2018

It looks pretty cool! Wednesday, Jan 10 Invited Talk: Predictive information criteria in hierarchical Bayesian models for clustered data. Sophia Rabe-Hesketh and Daniel Furr (U California, Berkely) 10:40-11:30am Does the New York City Police Department rely on quotas? Jonathan Auerbach (Columbia U) 11:30-11:50am Bayesian estimation of mechanical elastic constants. Ben Bales, Brent Goodlet, Tresa Pollock, […]

## Stan Roundup, 10 November 2017

We’re in the heart of the academic season and there’s a lot going on. James Ramsey reported a critical performance regression bug in Stan 2.17 (this affects the latest CmdStan and PyStan, not the latest RStan). Sean Talts and Daniel Lee diagnosed the underlying problem as being with the change from char* to std::string arguments—you […]

## Stan Roundup, 27 October 2017

I missed two weeks and haven’t had time to create a dedicated blog for Stan yet, so we’re still here. This is only the update for this week. From now on, I’m going to try to concentrate on things that are done, not just in progress so you can get a better feel for the […]