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

Known groups validity: comparison of IRLS total score and subscale scores according to severity of sleep problems. P<0.0001 for mild versus moderate, mild versus severe, and moderate versus severe for IRLS total score, IRLS symptoms subscale score, and IRLS symptoms impact subscale score (Mann–Whitney–Wilcoxon test). Mild, moderate, and severe groups based on upper, middle, and lower tertile scores from the sleep problems index II of the MOS sleep scale.

Clinical validity: comparison of IRLS total and subscale scores among CGI-S groups. P<0.0001 for 3–5 versus 6–7, P<0.01 for 1–2 versus 6–7, and P=NS for 1–2 versus 3–5 for IRLS total score, IRLS symptoms subscale score, and IRLS symptoms impact subscale score (Mann–Whitney–Wilcoxon test). CGI-S group 1–2 includes ‘normal, not at all ill’ and ‘borderline ill patients’; group 3–5 included ‘mild’, ‘moderate’, and ‘markedly ill’ patients; and group 6–7 includes patients who were ‘severely ill’ or ‘among the most extremely ill patients’.

Responsiveness as determined by change in IRLS total and subscale scores from baseline to week 12: effect sizes are compared among CGI-I groups. The single patient with a CGI-I score of ‘very much worse’ is not included, as effect sizes cannot be calculated for one person. P<0.0001 for comparisons among groups for the IRLS total score, symptoms and symptoms impact scores (Kruskall-Wallis test). Effect sizes were considered in the range of 0.2, small; 0.5, moderate; and 0.8, large .