Model comparison based on the Bayesian Information Criterion and random effects EM estimation.

Key: ‘b’ return sensitivity, so that ‘bb’ refers to a model with separate appetitive and aversive sensitivity; ‘a’ learning rate; ‘p’ Pavlovian bias; ‘l’ lapse rate; ‘g’ Go-bias (favoring action over inaction). Separate iBIC for the two groups, and also the total sample, are shown in columns. Using a single set of parameters to describe the group distributions for the healthy and control groups achieves a better score, by about 61 BIC units, than summing the best of each separate fit. Were one to fit the two groups separately, one would run a danger of over-fitting, here over-emphasizing differences between the groups.