Hi all! FYI: we (Gertjan Verhoeven & Misja Mikkers) wrote up a straightforward application / tutorial of Poisson regression using brms on a simulated dataset. The dataset is generated mimicking a perfect Randomized Controlled Trial (RCT). The post explains how to use the brms::posterior_predict() function with new data to calculate the posterior distribution of model derived quantities such as an average treatment effect (ATE).
The post is here: https://gsverhoeven.github.io/post/posterior-distribution-average-treatment-effect/
Feedback welcome!