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

Outcome at 3 years	Interferon	Placebo	Adjusted 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 MS	35%	50%	51% (27 to 67)	4 (2 to 8)