Factor Analysis in the Evaluation of Criteria and Variants of Systemic Lupus Erythematosus

Abstract

The value of factor analysis in defining complex diseases was tested with a series of 135 patients with more or less evidence of systemic lupus erythematosus (SLE).The factor analytic classification of the patients according to the interdependence of 25 unweighed criteria for’ SLE concurred rather well with a clinical classification into definite, probable, and possible SLE cases obtained by transforming the »diagnostic«, »major«, and »minor« criteria into numerical values. The clinical evaluation of the criteria appeared thus to have a sound statistic basis, even if there was evidence of that too much confidence had been paid to the diagnostic value of certain criteria, especially in oligosymptomatic cases.Five factors corresponded to a clinically meaningful symptom complex or variant of SLE: the classical visceral and erythematous types of SLE, and rheumatoid, discoid and drug associated variants. This suggests that the factorial structure of SLE obtained in this study is rather invariant, i.e., susceptible to profound alterations neither by réévaluation with other series nor by addition of new characteristics to the set of criteria for SLE.