Development of an instrument to measure pain in rheumatoid arthritis: The Rheumatoid Arthritis Pain Scale (RAPS)

The concept of pain in rheumatoid arthritis has not been well researched. Those treating rheumatic disease seem to classically define pain in rheumatoid arthritis in terms of the medical model only, rather than as a combination of factors. The need for an instrument to assess and measure pain in rheumatoid arthritis was the problem addressed by this study.

The theoretical framework for the research study was developed around the Gate Control Theory of pain. The Rheumatoid Arthritis Pain Scale (RAPS), reflects the nature and complexity brought forth in the Gate Control Theory by including items that represent the total pain experience in rheumatoid arthritis, those being: sensory-discriminative, physiological, affective and cognitive.

Psychometric evaluation of the 24-item instrument was conducted following estimation of content validity and a subsequent pilot study. A convenience sample of 120 adults, 18 years of age or older residing in a large metropolitan southwestern city, participated in the study. Participants were recruited from a large private physician practice setting. All responses were anonymous and participation was voluntary.

Data were analyzed using Cronbach's coefficient alpha, Pearson product-movement correlation coefficients and exploratory factor analysis. The findings resulted in an instrument with 24 items. Coefficient alphas for the 24-item total instrument was.92. Coefficient alphas for the subscales were: sensory-discriminative,.8; physiologic,.7; cognitive,.86; and affective,.64. Most item to total correlations ranged from.3 to.7. Item to item correlations ranged from.08 to.82. The item-subscale correlations ranged from.64 to.86.

Exploratory factor analysis yielded three factors with criteria for factor loadings.40 or higher. Criterion based concurrent validity of the instrument was assessed through theoretically predicted relationships between the RAPS and the Modified Visual Analogue Scale, measuring pain intensity, and total joint count, an indicator of disease process.

The study's findings provided initial support for the RAPS as a reliable and valid measurement of pain in rheumatoid arthritis. A valid and reliable instrument can assist the study of pain in this disease process. Assessment of pain and the relationship of pain to treatment outcomes could have significant impact for patients and medical and nursing practice.