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Regression to the mean in multiple sclerosis

Multiple Sclerosis Unit, Service of Neurology, Hospital Universitari de Bellvitge, IDIBELL, l’Hospitalet de Llobregat, Barcelona 08907, Spain

A Martínez-Yélamos

Service of Neurology, Hospital de Viladecans, Viladecans, Barcelona 08840, Spain

G Martín Ozaeta

Multiple Sclerosis Unit, Service of Neurology, Hospital Universitari de Bellvitge, IDIBELL, l’Hospitalet de Llobregat, Barcelona 08907, Spain

V Casado

Multiple Sclerosis Unit, Service of Neurology, Hospital Universitari de Bellvitge, IDIBELL, l’Hospitalet de Llobregat, Barcelona 08907, Spain

O Carmona

Service of Neurology, Hospital de Figueres, Girona 17600, Spain

Tx Arbizu

Multiple Sclerosis Unit, Service of Neurology, Hospital Universitari de Bellvitge, IDIBELL, l’Hospitalet de Llobregat, Barcelona 08907, Spain, unitatem{at}scs.csub.es

In order to ensure sufficient disease activity, patients with relapsing remitting (RR) multiple sclerosis (MS) are often included in randomized placebo-controlled trials, only if they have a high baseline activity. These patients, whose evolution is unusual in the pre-study period, will tend to show a more usual behavior when followed up over a period of time. This phenomenon is known as regression to the mean. Regression to the mean should be taken into account in correctly interpreting long-term studies of cohorts treated without a placebo control group, which use the baseline period as control. The aim of this study was to evaluate the relevance of this phenomenon in a non-treated cohort of RRMS patients, selected with similar criteria to those used in randomized placebo-controlled clinical trials. Forty-four patients with definite RRMS, with two or more relapses in the previous two years, and a baseline EDSS 5.5 were prospectively followed. The mean number of relapses spontaneously decreased from 1.72 (SD: 1.4) in the year prior to enrolment, to 1.0 (SD: 1.3) during the first year of follow-up (PB < 0.05). Regression to the mean may explain as much as 40% of the reduction in the relapse rate from the baseline period to the period on-study.

Key Words: disability • glatiramer acetate • interferon beta • multiple sclerosis • randomized clinical trials • regression to the mean

Multiple Sclerosis, Vol. 12, No. 6, 826-829 (2006)
DOI: 10.1177/1352458506070820


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