Exercises: Mixed models

Treatment of schizophrenia: Risperidone vs. haloperidol

1. Analyze the original data from Möller et al. (2008).
   • pans: Positive and Negative Symptom Scale for schizophrenia
   • treat: medication group
     • risp: atypical neuroleptic risperidone
     • halo: conventional neuroleptic haloperidol
   • What is the sample size in each treatment group?
   • Estimate the by-group random-slope model.
   • What are the estimates for the fixed effects and variance components?
   • Interpret the interaction effect.
   • Test the interaction effect.

dat <- read.table("../data/moeller.csv", header = TRUE, sep = ",")
dat$id <- factor(dat$id)
dat$treat <- factor(dat$treat, levels = c("risp", "halo"))
lattice::xyplot(pans ~ week, data = dat, groups = treat,
                type = c("g", "p", "a"))

2. Run a power simulation for a replication study:
   • Set up a data frame containing the study design and sample size.
   • Specify the minimum relevant effect.
   • Set the fixed effects and variance components to plausible values.
   • How many participants are required for the test of the interaction to detect the specified effect with a power of 80%?
   • Recover the parameters of the by-group random-slope model for one simulated data set.

Reference

Möller, H.-J., M. Riedel, M. Jäger, F. Wickelmaier, W. Maier, K.-U. Kühn, G. Buchkremer, et al. 2008. “Short-Term Treatment with Risperidone or Haloperidol in First-Episode Schizophrenia: 8-Week Results of a Randomized Controlled Trial Within the German Research Network on Schizophrenia.” International Journal of Neuropsychopharmacology 11 (7): 985–97. https://doi.org/10.1017/S1461145708008791.