Pooled historical MRI data as a basis for research in multiple sclerosis--a statistical evaluation.

Pooled data from placebo groups of different trials can serve as historical control for ongoing or future therapeutic studies and as a reference for power calculations. In order to assess their usefulness for this purpose, we investigated the degree of heterogeneity of placebo arm data from 14 controlled studies included in the database of the Sylvia Lawry Centre for Multiple Sclerosis Research. Since different criteria for the inclusion/exclusion of patients were used in these studies, an attempt was made to adjust the distribution of magnetic resonance imaging (MRI) measures for the differences in the study populations. The analyses showed that, even after adjustment, significant differences remained. This heterogeneity does not reduce the usefulness of the database for statistical analysis of inter-relationships between variables, provided that it is explicitly taken into account as a stratification factor. However, care must be taken when trying to compare the results of a newly treated group with the patients of this pool. Heterogeneity in some MRI variables was greatly reduced when only studies from the same image analysis centre were compared.