BFDA and ordinal models in BRMS

Implementing Bayes Factor Design Analysis for a 3x3 repeated measures design and analyzing the results in BRMS using an ordinal model.

3 experimental and sequential blocks with randomization within the block. Each block includes X stimuli followed by a dichotomous question and then one or two Likert scale items.

The decisions made by a participant in one block will have an impact on their decisions in the next block.

I believe that the predictors will have the same effect on all response categories.

How would I implement the methodology set out by Stefan et al. (2019) and Stefan et al. (2024) to plan and then continuously assess the number of participants needed to reach a Bayes Factor of 6 in a sequential procedure.

There is to my knowledge no research available that could aid me in informing me on priors. This firs experiment will be a pilot.

I would like to predict the answer to the dichotomous choice and the rating for the Likert scale data using the 3x3 categories of the stimuli.

Would anyone be keen on helping me out?

I’m running macOS Sonoma 14.4.1. RStudio version 2023.12.1+402 (2023.12.1+402). BRMS version 2.21.0.

Thanks!

Stefan, A. M., Gronau, Q. F., & Wagenmakers, E.-J. (2024, February 8). Interim Design Analysis Using Bayes Factor Forecasts. Psychological Methods. Advance online publication. APA PsycNet

Schönbrodt, F. D., & Wagenmakers, E-J. (2019). Bayes Factor Design Analysis: Planning for Compelling Evidence.