What is the maximum number of levels needed in pain intensity measurement?

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Abstract
An important issue that has yet to be resolved in pain measurement literature concerns the number of levels needed to assess self-reported pain intensity. An examination of treatment outcome literature shows a large variation in the number of levels used, from as few as 4 (e.g., 4-point Verbal Rating scales (VRS)) to as many as 101 (e.g., 101-point Numerical Rating scales (NRS)). The purpose of this study was to provide an empirically derived guideline for determining the number of levels needed. Chronic pain patients (n = 124) provided pre- and post-treatment measures of pain intensity using 101-point NRS for least, most, current, and average pain. The patients' responses to the measures were examined closely to determine the actual number of levels used. In addition, their responses to the 101-point scales were recorded to form 7 scales of varying levels (2- to 101-point scales). The sensitivity of the 7 recorded scales was examined. The results indicated that little information is lost if 101-point scales are coded as 11- or 21-point scales. Moreover, examination of the actual responses to the 101-point measure showed that almost all patients treated it as a 21-point scale by providing responses in multiples of 5 or 10, while a substantial number of patients treated it as an 11-point scale, providing responses in multiples of 10 only. The results suggest that 10- and 21-point scales provide sufficient levels of discrimination, in general, for chronic pain patients to describe pain intensity.