[LONGITUDINAL] input = {a,b} EQUATION: lp0 = a-b*t lp1 = a-b*t/2 p0 = 1/(1+exp(-lp0)) p1 = 1/(1+exp(-lp1)) -p0 p2 = 1-p0-p1 DEFINITION: y = {type = categorical, categories = {0, 1, 2}, P(y=0) = p0, P(y=1) = p1}