To the Editor.
—Epidemiologic studies of multiple sclerosis (MS) assessing risk factors for disease causation or exacerbation and progression are problematic for several reasons. One of the most important reasons is that little attention has been paid to the selection of control subjects with whom patients with MS have been compared to evaluate potential risk factors.For attempts to determine the actual cause of the disease, healthy control subjects must be used, preferably those who share a common ethnic and genetic background with the study group. For those factors thought to influence the course of the already acquired illness, resulting in exacerbations, only other patients with MS can be suitable control subjects.Many epidemiologic studies have attempted to assess the relationship of clinical symptoms to disease activity by matching for such factors as age, sex, degree of disability, number of exacerbations, date of onset of disease, and duration of disease.
Poser CM, Hibberd PL. Epidemiologic Studies of Multiple Sclerosis. Arch Neurol. 1987;44(3):251–252. doi:10.1001/archneur.1987.00520150007006