McGill University Biostatistics seminar, Purvis Hall, 102 Pine Ave. West, Room 25 Education Building, 3700 McTavish Street, Room 129 [note new location], 1-2pm Fri 22 Mar: Resolving the Replication Crisis Using Multilevel Modeling In recent years we have come to learn that many prominent studies in social science and medicine, conducted at leading research institutions, […]

**Bayesian Statistics**category.

## He asks me a question, and I reply with a bunch of links

Ed Bein writes: I’m hoping you can clarify a Bayesian “metaphysics” question for me. Let me note I have limited experience with Bayesian statistics. In frequentist statistics, probability has to do with what happens in the long run. For example, a p value is defined in terms of what happens if, from now till eternity, […]

## Maybe it’s time to let the old ways die; or We broke R-hat so now we have to fix it.

“Otto eye-balled the diva lying comatose amongst the reeds, and he suddenly felt the fire of inspiration flood his soul. He ran back to his workshop where he futzed and futzed and futzed.” –Bette Midler Andrew was annoyed. Well, annoyed is probably too strong a word. Maybe a better way to start is with The […]

## Estimating treatment effects on rates of rare events using precursor data: Going further with hierarchical models.

Someone points to my paper with Gary King from 1998, Estimating the probability of events that have never occurred: When is your vote decisive?, and writes: In my area of early childhood intervention, there are certain outcomes which are rare. Things like premature birth, confirmed cases of child-maltreatment, SIDS, etc. They are rare enough that […]

## R package for Type M and Type S errors

Andy Garland Timm writes: My package for working with Type S/M errors in hypothesis testing, ‘retrodesign’, is now up on CRAN. It builds on the code provided by Gelman and Carlin (2014) with functions for calculating type S/M errors across a variety of effect sizes as suggested for design analysis in the paper, a function […]

## “We’ve Got More Than One Model: Evaluating, comparing, and extending Bayesian predictions”

I was asked to speak at the American Association of Pharmaceutical Scientists Predictive Modeling Workshop, and a title was needed. This is what I came up with: We’ve Got More Than One Model: Evaluating, comparing, and extending Bayesian predictions It’s the Bayesian Workflow stuff we’ve been pushing for awhile. But I like this new title.

## HMC step size: How does it scale with dimension?

A bunch of us were arguing about how the Hamiltonian Monte Carlo step size should scale with dimension, and so Bob did the Bob thing and just ran an experiment on the computer to figure it out. Bob writes: This is for standard normal independent in all dimensions. Note the log scale on the x […]

## “Do you have any recommendations for useful priors when datasets are small?”

Someone who wishes to remain anonymous writes: I just read your paper with Daniel Simpson and Michael Betancourt, The Prior Can Often Only Be Understood in the Context of the Likelihood, and I find it refreshing to read that “the practical utility of a prior distribution within a given analysis then depends critically on both […]

## Our hypotheses are not just falsifiable; they’re actually false.

Everybody’s talkin bout Popper, Lakatos, etc. I think they’re great. Falsificationist Bayes, all the way, man! But there’s something we need to be careful about. All the statistical hypotheses we ever make are false. That is, if a hypothesis becomes specific enough to make (probabilistic) predictions, we know that with enough data we will be […]

## Fitting multilevel models when the number of groups is small

Matthew Poes writes: I have a question that I think you have answered for me before. There is an argument to be made that HLM should not be performed if a sample is too small (too small level 2 and too small level 1 units). Lot’s of papers written with guidelines on what those should […]

## Of multiple comparisons and multilevel models

Kleber Neves writes: I’ve been a long-time reader of your blog, eventually becoming more involved with the “replication crisis” and such (currently, I work with the Brazilian Reproducibility Initiative). Anyway, as I’m now going deeper into statistics, I feel like I still lack some foundational intuitions (I was trained as a half computer scientist/half experimental […]

## Transforming parameters in a simple time-series model; debugging the Jacobian

So. This one is pretty simple. But the general idea could be useful to some of you. So here goes. We were fitting a model with an autocorrelation parameter, rho, which was constrained to be between 0 and 1. The model looks like this: eta_t ~ normal(rho*eta_{t-1}, sigma_res), for t = 2, 3, … T […]

## Data partitioning as an essential element in evaluation of predictive properties of a statistical method

In a discussion of our stacking paper, the point came up that LOO (leave-one-out cross validation) requires a partitioning of data—you can only “leave one out” if you define what “one” is. It is sometimes said that LOO “relies on the data-exchangeability assumption,” but I don’t think that’s quite the right way to put it, […]

## “The Book of Why” by Pearl and Mackenzie

Judea Pearl and Dana Mackenzie sent me a copy of their new book, “The book of why: The new science of cause and effect.” There are some things I don’t like about their book, and I’ll get to that, but I want to start with a central point of theirs with which I agree strongly. […]

## Did she really live 122 years?

Even more famous than “the Japanese dude who won the hot dog eating contest” is “the French lady who lived to be 122 years old.” But did she really? Paul Campos points us to this post, where he writes: Here’s a statistical series, laying out various points along the 100 longest known durations of a […]

## Objective Bayes conference in June

Christian Robert points us to this Objective Bayes Methodology Conference in Warwick, England in June. I’m not a big fan of the term “objective Bayes” (see my paper with Christian Hennig, Beyond subjective and objective in statistics), but the conference itself looks interesting, and there are still a few weeks left for people to submit […]

## “Principles of posterior visualization”

What better way to start the new year than with a discussion of statistical graphics. Mikhail Shubin has this great post from a few years ago on Bayesian visualization. He lists the following principles: Principle 1: Uncertainty should be visualized Principle 2: Visualization of variability ≠ Visualization of uncertainty Principle 3: Equal probability = Equal […]

## “Check yourself before you wreck yourself: Assessing discrete choice models through predictive simulations”

Timothy Brathwaite sends along this wonderfully-titled article (also here, and here’s the replication code), which begins: Typically, discrete choice modelers develop ever-more advanced models and estimation methods. Compared to the impressive progress in model development and estimation, model-checking techniques have lagged behind. Often, choice modelers use only crude methods to assess how well an estimated […]

## What is probability?

This came up in a discussion a few years ago, where people were arguing about the meaning of probability: is it long-run frequency, is it subjective belief, is it betting odds, etc? I wrote: Probability is a mathematical concept. I think Martha Smith’s analogy to points, lines, and arithmetic is a good one. Probabilities are […]

## Exploring model fit by looking at a histogram of a posterior simulation draw of a set of parameters in a hierarchical model

Opher Donchin writes in with a question: We’ve been finding it useful in the lab recently to look at the histogram of samples from the parameter combined across all subjects. We think, but we’re not sure, that this reflects the distribution of that parameter when marginalized across subjects and can be a useful visualization. It […]