The development of the Restless Legs Syndrome-Next Day Impact (RLS-NDI) questionnaire included concept elicitation interviews with RLS patients in the United States (n = 20); grounded theory data collection and analysis methods; and review by clinical and measurement experts to generate items, responses, and instructions. Cognitive interviews (n = 15) were conducted to ensure understanding of the RLS-NDI, concept comprehensiveness, and identification of any necessary item revisions.
Impacts on next day functioning attributed to disturbed sleep due to RLS symptoms included activities of daily living (i.e., work, household chores), cognitive functioning (i.e., concentration, forgetfulness, mental tiredness, alertness), emotional functioning (i.e., irritability, depressed mood), physical functioning (i.e., physical tiredness, active leisure activities), energy, daytime sleepiness, and social functioning (i.e., relationships, social activities/situations). The final measure consists of 14 items assessed ¡°today?and rated on a numeric rating scale.
The RLS-NDI is an evaluative tool with demonstrated content validity.