Item-response-theory analysis of two scales for self-efficacy for exercise behavior in people with arthritis.

Benefits of physical activity for those with arthritis are clear, yet physical activity is difficult to initiate and maintain. Self-efficacy is a key modifiable psychosocial determinant of physical activity. This study examined two scales for self-efficacy for exercise behavior (SEEB) to identify their strengths and weaknesses using item response theory (IRT) from community-based randomized controlled trials of physical activity programs in adults with arthritis. The 2 SEEB scales included the 9-item scale by Resnick developed with older adults and the 5-item scale by Marcus developed with employed adults. All IRT analyses were conducted using the graded-response model. IRT assumptions were assessed using both exploratory and confirmatory factor analysis. The IRT analyses indicated that these scales are precise and reliable measures for identifying people with arthritis and low SEEB. The Resnick SEEB scale is slightly more precise at lower levels of self-efficacy in older adults with arthritis.