SSF: Simulation function to assess power of mixed models
Description
Given a specific total number of observations and variance-covariance structure for random
effect, the function simulates different association of number of
group and replicates (giving the specified sample size) and assess p-values and power of random
intercept and random slope
number of group*replicates associations to simulate
randompart
vector of lenght 4 or 5 with 1) variance component
of intercept (VI); 2) variance component of slope (VS); 3) residual
variance (VR); 4) relation between random intercept and random
slope; 5) "cor" or "cov" determine id the relation between I
fixed
vector of lenght 3 with mean, variance and estimate of fixed effect to simulate
intercept
a numeric value giving the expected intercept value. Default:0
exgr
a vector specifying minimum and maximum value for number of group. Default:c(2,tss/2)
exrepl
a vector specifying minimum and maximum value for number of replicates. Default:c(2,tss/2)
Value
data frame reporting estimated P-values and power with CI for random
intercept and random slope
Warning
the simulation is based on a balanced data set with
unrelated group
Details
P-values for random effects are estimated using a log-likelihood ratio
test between two models with and without the effect. Power represent
the percentage of simulations providing a significant p-value for a
given random structure