one of c(beta1", "beta2", "b1", "b2", a.x", "a.c",
"b.c", "SAM", "AS", "SSDO", "circ.diff", "omega1", "omega2", "cRI", "cRS")
to indicate for which parameter a traceplot is required. beta1 and
beta2 are the fixed effects coefficients of a mixed-effects model.
b1 and b2 are the random effects coefficients of a
mixed-effects model. circ.diff are the circular differences with the
intercept on the outcome variable for the different levels of categorical
variables. omega1 and omega2 are the linear random effect
variances and cRI and cRS are the variances of the circular
random intercept and circular random slope.