el comparison method that uses WAIC (default method) to estimate the expected prediction error of the four models and select the most appropriate model given the data. The first round of model comparisons sets up model types, "gplm" vs. "gplm0" and "plm" vs. "plm0". The two comparisons are conducted such that if the WAIC of the more complex model ("gplm" and "plm", respectively) is smaller than the WAIC of the simpler models ("gplm0" and "plm0", respectively) by an input argument called the <code>winning_cr