The special functions
ri are used to specify
unit-specific effects of covariates and random intercept terms,
respectively, in the component formulae of
fe(x, unitSpecific = FALSE, which = NULL, initial = NULL) ri(type = c("iid","car"), corr = c("none", "all"), initial.fe = 0, initial.var = -.5, initial.re = NULL)
an expression like
sin(2*pi*t/52) involving the time
t, or just
1 for an intercept.
In general this covariate expression might use any variables
contained in the
control$data argument of the parent
logical indicating if the effect of
should be unit-specific. This is a convenient shortcut for
which = rep(TRUE, nUnits), where
nUnits is the number
of units (i.e., columns of the
vector of logicals indicating which unit(s)
should get an unit-specific parameter.
For units with a
value, the effect term for
x will be zero in the log-linear
predictor. Note especially that setting a
FALSE value for the
intercept term of a unit, e.g.,
ar = list(f = ~-1 + fe(1, which=c(TRUE, FALSE)))
in a bivariate
hhh4 model, does not mean that the
(autoregressive) model component is omitted for this unit, but that
\(\log(\lambda_1) = \alpha_1\) and \(\log(\lambda_2) = 0\), which
is usually not of interest. ATM, omitting an autoregressive effect for
a specific unit is not possible.
which=NULL, the parameter is assumed to be the same
for all units.
initial values (on internal scale!)
for the fixed effects used for optimization. The default
NULL) means to use zeroes.
random intercepts either follow an IID or a CAR model.
whether random effects
in different components (such as
should be correlated or not.
initial value for the random intercept mean.
initial values (on internal scale!) for the variance components used for optimization.
initial values (on internal scale!) for the random effects
used for optimization. The default
NULL are random numbers
from a normal distribution with zero mean and variance 0.001.
hhh4 model specifications in
vignette("hhh4_spacetime") or on the help page of
These special functions are intended for use in component formulae of
hhh4 models and are not exported from the package namespace.
If unit-specific fixed or random intercepts are specified, an overall
intercept must be excluded (by
-1) in the component formula.