The reliability, validity and responsiveness of the International Restless Legs Syndrome Study Group rating scale and subscales in a clinical-trial setting

Abstract 

Patients and methods

To assess the reliability, validity, and responsiveness of the International Restless Legs Syndrome Study Group's rating scale (the International Restless Legs Scale (IRLS)) (V2.0), using pooled data from two matching, placebo-controlled studies of ropinirole for treating Restless Legs Syndrome (RLS).

Results

Pooled patient samples comprised 550 patients in the baseline (validation) sample and 439 patients in the week 12 longitudinal (responsiveness) sample. Factor analysis revealed acceptability of the IRLS total score (accounting for 40% of the variance) and that nine of the 10 IRLS items could also be assigned to two distinct subscales, the symptoms or symptoms impact subscales. The IRLS total score, symptoms and symptoms impact subscales had acceptable construct validity, internal consistency reliability (α=0.81, 0.80, and 0.76, respectively), and concurrent validity (r=−0.68, −0.52, −0.70, respectively, with the Restless Legs Syndrome Quality of Life questionnaire (RLSQoL) overall life impact score). IRLS scores differed significantly between different levels of sleep problems and Clinical Global Impression (CGI) of health status (P<0.0001), indicating known groups and clinical validity, respectively. Changes in scores differed significantly among CGI ‘global improvement’ levels (P<0.0001), providing evidence of responsiveness.

Conclusions

The IRLS total score, symptoms, and symptoms impact subscales are reliable, valid, and responsive in a clinical trial setting.

Keywords: IRLS, Restless legs syndrome, Reliability, Validity, Responsiveness, Psychometric analysis