summary: Whether summary statistics should be returned instead of raw sample values. Defaults to TRUE
probs: The percentiles used to compute summary, defaults to 89% credible interval.
includePopulationLevel: Logical, for pooled random effect only. Whether to include population mean as a separate "_population" level, default to TRUE.
Returns
A single value, if fixed value was used. A vector or a tibble, depending on the option used (single intercept, independent or random intercepts), and whether summary was requested.