one of c("b1", "b2", beta1", "beta2", 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 linear intercepts and coefficients of the first and
second component for a regression model and 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.