Altman RM et al. – Sample sizes based on the longitudinal model are more realistic and often smaller than those previously reported using the negative binomial (NB) model.Methods
- The fit of the NB model in each arm of five MS clinical trials was assessed using Pearson’s chi-squared statistic.
- Required sample sizes associated with various tests of treatment effect were estimated by simulating data from a new, longitudinal model for repeated lesion count data on individual patients.
- Evidence (p < 0.05) against the NB model was found in at least one arm of four of the five trials.
- If a trial is designed using this model but the resulting clinical data do not follow its assumptions then this trial can be seriously under-powered for assessing differences in mean lesion counts.