Impossible values included in credible interval
I am preforming a mixed BANOVA with RMSE as the dependent variable. I noticed that in the descriptives the credible intervals include negative values (which are of course impossible). It seems that the credible interval is centered around the mean, even when all deviations from the mean are positive. Is it possible to modify the analysis so that credible intervals do not extend below 0? What setting is in that case needed? How come the credible interval centers on the mean even though deviations from the mean are skewed?