Aki Vehtari

Bayes Club A community of statisticians using Bayesian methods.

If you feel so inclined, I run a Mastodon instance bayes.club and try to make it a nice place and you can join if you like. I know some people have strong opinions on this and some have had bad experience on Mastodon. And that's all fair and I won't dispute that, there's a lot of work to do.

ELLIS PhD Program: Call for Applications 2025 The ELLIS mission is to create a diverse European network that promotes research excellence and advances breakthroughs in AI, as well as a pan-European PhD program to educate the next generation of AI...

I'm looking for a doctoral student with Bayesian background to work on Bayesian workflow and cross-validation (see my publication list users.aalto.fi/~ave/publica... for my recent work) at Aalto University.

Apply through the ELLIS PhD program (dl October 31) ellis.eu/news/ellis-p...

Photo of Porto Giunco beach at Sardinia

Photo of many kite surfers at Punta Trettu, Sardinia

I was two weeks on vacation in sunny and warm Sardinia, Italy, played in a beach ultimate tournament (this year we were the 4th best team in the world, and the best non-USA team), learned to kite surf, snorkeled, and ate lots of delicious food and gelato

Production repository – R-multiverse A community-curated dual R package repository, powered by R-universe

R-multiverse Production repository r-multiverse.org/production.h... looks great for those who prefer CRAN level stability (actually a bit more stable) for R packages, but want to also use high quality packages that are not in CRAN (like CmdStanR)

Whoa—my book is up for pre-order!

𝐌𝐨𝐝𝐞𝐥 𝐭𝐨 𝐌𝐞𝐚𝐧𝐢𝐧𝐠: 𝐇𝐨𝐰 𝐭𝐨 𝐈𝐧𝐭𝐞𝐫𝐩𝐫𝐞𝐭 𝐒𝐭𝐚𝐭 & 𝐌𝐋 𝐌𝐨𝐝𝐞𝐥𝐬 𝐢𝐧 #Rstats 𝐚𝐧𝐝 #PyData

The book presents an ultra-simple and powerful workflow to make sense of ± any model you fit

The web version will stay free forever and my proceeds go to charity.

tinyurl.com/4fk56fc8

30th Nordic Conference in Mathematical Statistics | University of Helsinki 1-4 June 2026, University of Helsinki, Finland

NordStat will be in Helsinki in 1-4 June, 2026. Website and preliminary program have been published:
www.helsinki.fi/en/conferenc...

MC Stan is here! Follow for the latest Stan news, and tag if you want us to repost your posts about new papers, packages, courses, etc. about Stan

Stats and ML postdoc and permanent hiring season officially open at Flatiron
statmodeling.stat.columbia.edu/2025/09/16/s...

Working with stat_manual() – Væl Space

for the late nite crew: stat_manual() is super good

Optimal pandemic control strategies and cost-effectiveness of COVID-19 non-pharmaceutical interventions in the United States - BMC Global and Public Health Background Non-pharmaceutical interventions (NPIs) in response to the COVID-19 pandemic necessitated a trade-off between the health impacts of viral spread and the social and economic costs of restric...

Our paper, “Optimal pandemic control strategies …” bmcglobalpublichealth.biomedcentral.com/articles/10.... w @nickirons.bsky.social, just published.Takeaway: U.S. COVID-19 school closures were not cost-effective, but other measures were. medicalxpress.com/news/2025-09...

ggplot2 4.0.0 A new major version of ggplot2 has been released on CRAN. Find out what is new here.

I am beyond excited to announce that ggplot2 4.0.0 has just landed on CRAN.

It's not every day we have a new major #ggplot2 release but it is a fitting 18 year birthday present for the package.

Get an overview of the release in this blog post and be on the lookout for more in-depth posts #rstats

The Journal-to-Conference track is back at AISTATS🌴!

The track invites authors of papers published or accepted after January 1st, 2024 in AoS, Biometrika, JASA, JMLR and JRSS B to present their work as posters at #AISTATS2026 in Tangier, Morocco (May 2nd-5th 2026).

📅 Deadline: 31 January 2026

output from a GAM in the linked essay

Simon Wood, the GOAT of generalized additive models & creator of the mgcv #rstats package, has an Annual Review of Statistics essay on GAMs, available open access #statssky #mlsky

www.annualreviews.org/content/jour...

Promotional poster for the LMU Open Science Center Summer School 2025 Public Lecture. The poster features a photo of speaker Prof. Dr. Richard McElreath. The text states the lecture focuses on science as amateur software development, time and date of lecture being 9:00-10:00 CEST on Wednesday September 17 2025, and instructions to register online. Logos of LMU Open Science Center, LMU, and Universitätsbibliothek München are displayed at the bottom.

💡 Explore how practices from distributed, open-source software can make science more professional, open, and collaborative! Attend the “Science as amateur software development” lecture by Prof. Dr. @rmcelreath.bsky.social on Wed 17 Sept, 9:00.
👉 Register here: www.pretix.osc.lmu.de/lmu-osc/OSSS...

Tidybayes and ggdist might have something useful for your packages

We are seeking a postdoctoral researcher in statistics to develop methods for analyzing large scale biodiversity and ecosystem function data at the University of Helsinki.

This is a great opportunity for someone who wants to do advanced Bayesian modeling with direct link to real world applications.

And the discrete rootogram with white background

- Add x argument to ppc_error_binned() and ppc_error_scatter_avg() to control x axis
- Add discrete argument to pp[cd]_stat() to support discrete stats

3/3

other new features
- PPC “avg” functions gain a stat argument to set the summary function
- ppc_error_scatter_avg_vs_x(x = some_expression) labels the x axis with some_expression.
- New quantile dot plot functions pp[cd]_dots()

2/3

A discrete rootgram plot. The unmodified counts are displayed on the vertical axis, while using square root scaling for the axis, thus enabling direct reading of the count frequencies. The predictions are displayed as light blue points and interval lines. The observations are overlaid with darker points, except the observations outside the predictive credible intervals are highlighted in red.

bayesplot 1.14.0 CRAN release mc-stan.org/bayesplot/ with contributions from @tjmahr.com, Behram Ulukır, and @teemusailynoja.bsky.social

My favorite new feature is the discrete style ppc_rootogram() as proposed in teemusailynoja.github.io/visual-predi... and shown below

1/3

Productive procrastination by making 7 PRs to fix Stan doc issues (still couple issues I think I can help with)

- new hypergeometric functions
- C++17 features improve performance
CmdStan:
- easier to run multiple chains with one call to the executable
- improved error messages
- default output use more digits to reduce constraint errors when reusing output
- laplace_sample and Pathfinder use less memory
2/2

Release of CmdStan 2.37 We are very happy to announce that the 2.37.0 release of CmdStan is now available on Github! As usual, the release of CmdStan is accompanied by new releases of Stan Math, core Stan, and Stanc3. Thi…

Stan / CmdStan 2.37 release!
blog.mc-stan.org/2025/09/02/r...
- sum_to_zero_matrix type sums to zero across both rows and columns
- simplex and *_stochastic_matrix types should be now faster and more stable
- new functions exposing the built-in constraint implementations
1/2

In case of coffee price, I think more accurate statement is "climate change sucks"

My Bayesian Data Analysis course at Aalto is starting in 20mins. There are now 375 registered students, but as the course is not compulsory for most, I expect about 230 students to finish it. All the course material is available online at avehtari.github.io/BDA_course_A...

I think we'll get the Bayesian workflow book finished this year (and keep it under 500 pages). It's just polishing work now

I finally tried out {priorsense}📦 with #Stan #rstats and it's awesome!

Fed it a simple model I use for teaching, and found some (minor) prior-data conflicts. The powerscale_plot_dens() function really helps in understanding how "bad" the conflict is.

Juho Hirvonen and Jukka Suomela: Distributed Algorithms 2020 A free online textbook — introduction to the theory of distributed algorithms

Aalto University course "Distributed Algorithms" starts tomorrow! All course material (including an online textbook and short videos) are freely available here: jukkasuomela.fi/da2020/

🚨AISTATS workshop proposals open!

Big News: For the first time, there will be a day of workshops at #AISTATS 2026, in Tangier, Morocco 🌴🇲🇦

Quentin Berthet @qberthet.bsky.social and I are workshop chairs.

virtual.aistats.org/Conferences/...
Deadline: Oct 17, AOE

Nice looking paper