Nothing
If pilot data is not available, simr
can be used to create lme4
objects from scratch as a starting point. This requires more paramters to be specified by the user. Values for these parameters might come from the literature or the user's own knowledge and experience.
library(simr)
simrOptions(nsim=100, progress=FALSE)
First set up some covariates with expand.grid
.
x <- 1:10 g <- letters[1:3] X <- expand.grid(x=x, g=g)
Specify some fixed and random parameters.
b <- c(2, -0.1) # fixed intercept and slope V1 <- 0.5 # random intercept variance V2 <- matrix(c(0.5,0.05,0.05,0.1), 2) # random intercept and slope variance-covariance matrix s <- 1 # residual standard deviation
Use the makeLmer
or makeGlmer
function to build an artificial lme4
object.
model1 <- makeLmer(y ~ x + (1|g), fixef=b, VarCorr=V1, sigma=s, data=X) print(model1) model2 <- makeGlmer(z ~ x + (x|g), family="poisson", fixef=b, VarCorr=V2, data=X) print(model2)
Now we have "pilot" models, which can be used with simr
.
powerSim(model1, nsim=20) powerSim(model2, nsim=20)
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