An item response analysis of the international restless legs syndrome study group rating scale for restless legs syndrome

Apr 1, 2005Sleep medicine

Detailed analysis of the global restless legs syndrome rating scale

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Abstract

Scores from 196 patients on the International Restless Legs Severity Scale (IRLS) demonstrate excellent item response properties.

The IRLS consists of 10 items designed to measure the severity of restless legs syndrome.
Each item on the IRLS showed a strong correlation with overall RLS severity.
Item 3, related to relief of discomfort from movement, exhibited a 'floor' effect, indicating it was less sensitive in lower severity ranges.
Despite the floor effect for Item 3, its response characteristics were still deemed acceptable.
The IRLS is supported by evidence of high reliability, validity, and internal consistency.

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BACKGROUND AND PURPOSE: Restless legs syndrome (RLS) is a common central nervous system disorder; however, there is currently a lack of well-validated and easily-administered measures of RLS severity available. The International Restless Legs Syndrome Study Group has recently developed a 10-item scale to meet this need. The International Restless Legs Severity Scale (IRLS) has been shown to have a high degree of reliability, validity, and internal consistency. In order to further demonstrate the validity of the IRLS, the present study examined the relationship between scores on individual IRLS items and overall RLS severity.

PATIENTS AND METHODS: The 10-item IRLS was administered to 196 RLS patients. Option characteristic curves (the probability of scoring different options for a given item as a function of overall IRLS score) were generated in order to illustrate the scoring patterns for each item across the range of total RLS severity. Item characteristic curves (the expected score on an item as a function of overall IRLS score) were also generated to illustrate the relationship between scores on the individual items and total RLS severity.

RESULTS: The IRLS items demonstrated excellent item response properties, with option and item characteristic curves closely approximating those of an ideal item. Item 3 (relief of arm or leg discomfort from moving around) was the most problematic item in that a 'floor' effect was evident; however, the item response characteristics for this item were still acceptable.

CONCLUSIONS: Each IRLS item showed a good relationship between responses on that item and overall RLS severity, providing further evidence for the validity of the IRLS as a measure of RLS severity in RLS patients.

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An item response analysis of the international restless legs syndrome study group rating scale for restless legs syndrome

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