Interferon β-1a v placebo to prevent multiple sclerosis (MS) after a first demyelinating event‡

Outcome at 3 yearsInterferonPlaceboAdjusted RRR (95% CI)§NNT (CI)
Abbreviations defined in glossary; NNT and its CI calculated from data in article.
§Adjusted for age, type of initial event, and volume of lesions on MRI scans.
Definite MS35%50%51% (27 to 67)4 (2 to 8)