Clinical surrogates of unremitting disability used in trials of relapsing-remitting multiple sclerosis cannot be validated. Trials have been too short or degrees of disability change too small to measure the key outcomes. These analyses highlight the difficulty in determining effectiveness of therapy in chronic diseases.

The relapse number prior to entry into clinical trials together with disease duration are the best predictors for the on-study relapse rate. Disease course did not contribute independently because its effect is covered by the pre-study relapse rate. Gadolinium enhancement status, given the other covariates, has no significant influence on the on-study relapse rate.

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