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

OBJECTIVE: To develop a valid and reliable clinical instrument for measuring pain in adult patients with rheumatoid arthritis. The resulting Rheumatoid Arthritis Pain Scale (RAPS) is a quantitative, single-score, self-report 24-item instrument.
METHODS: Psychometric evaluation of RAPS was conducted following estimation of content validity and a pilot study. The actual study used a convenience sample of 120 adults, 18 years of age or older, with pain of at least 3 months duration. The setting was a large rheumatology private practice in a metropolitan southwestern city. The gate control and affective motivational theories of pain served as a framework guiding the development of RAPS, which includes items suggestive of the multidimensional pain experience in rheumatoid arthritis. Four subscales, physiological, affective, sensory-discriminative, and cognitive, evaluated numerous pain factors.
RESULTS: Findings indicate a high estimate for internal consistency for the total scale and a moderate to high estimate of internal consistency for projected subscales. Data were analyzed using Cronbach's coefficient alpha, Pearson product-moment correlation coefficients, and exploratory factor analysis. Using Cronbach's coefficient alpha, RAPS showed an internal consistency reliability coefficient of 0.92, a strong indicator of reliability. Reliability assessments for the 4 subscales also indicate reliability, with Cronbach's coefficients ranging from 0.65 to 0.86. Exploratory factor analysis yielded 3 factors with criteria for factor loadings > or = 0.4.
CONCLUSION: The study's findings provided support for RAPS as a reliable and valid measurement of rheumatoid arthritis pain. Assessment of rheumatoid arthritis pain and its relationship to treatment outcomes could significantly impact the treatment interventions.