Factor analysis of the International Restless Legs Syndrome Study Group's scale for restless legs severity

Objective: The International Restless Legs Syndrome Study Group has developed and validated a ten-item scale for assessing the severity of the restless legs syndrome. This International Restless Legs Severity Scale (IRLS) is reported to have a high degree of internal consistency and it has generally been used as a single scale. This study uses a factor analytic approach to evaluate the IRLS for possibly useful subscales. Methods: A large convenience sample (n = 516) of self-identified restless leg syndrome patients completed the IRLS over the Internet. Data were analyzed using principal component analyses. Results: Two primary factors were identified, one with six items related to symptom severity and a second with three items related to impact of the symptoms on life. These accounted for 41.8 and 22.5% of the variance, respectively. Conclusions: The IRLS can be evaluated using separate subscale scores: one for symptoms and the other symptom impact. The relative merits of these subscale scores versus the score for the entire test need to be evaluated in different situations in further studies, in especially the ones involving assessing responsiveness to treatment effects.