A statistical method for quantitative evaluation of the progression of chronic diseases: the mean score graph (MSG).

We present a quantitative method of evaluation of the clinical course of chronic disease with long-term progressive deterioration. The method takes into account information on all patients, whatever their duration of follow-up. We present the 'mean score graph' as a descriptive device which is an extension of a survival graph. The description of progression of idiopathic torsion dystonia, comparing progression in males and females, is used as an example of the application. A test for group comparison is described.