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Covariate-Based Diagnostics for Randomized Experiments are Often Misleading

Over the last couple of years, I’ve seen a large number of people attempt to diagnose the quality of their randomized experiments by looking for imbalances in covariates, because they expect covariate imbalances to be ruled out by successful randomization. But imbalance is, in general, not guaranteed for any specific random assignment — and, as […]

What is an Interaction Effect?

Introduction Yesterday, Uri Simonsohn published a blog post called “Interactions in Logit Regressions: Why Positive May Mean Negative”. I love Uri’s blog in general, but I was pretty confused by this latest post. I found it very hard to understand exactly what was being claimed in the absence of formal mathematical definitions of the terms […]

Where Predictive Modeling Goes Astray

I recently reread Yarkoni and Westfall’s in-progress paper, “Choosing prediction over explanation in psychology: Lessons from machine learning”. I like this paper even more than I liked their previous paper, but I think a few notes of caution should be raised about the ways in which a transition to predictive modeling could create problems that […]