Specifies a univariate random effects model with two scale parameters
(SCALE1 & SCALE2). This command is used in conjunction with RVARIATE and
two sets of interactions to specify separate equations dependent upon
the value of a particular user-defined dummy variable. This dummy
variable could be defined by: (i) the lagged response variable, (ii) a
bivariate response variable indicator, or (iii) an initial response and
non-initial response indicator.