Validation studies of pain interference instruments used among student pharmacists are rare yet essential for understanding their appropriate use and interpretation in pharmacy education and practice. This study conducted validation and reliability assessments of a five-item Pain Interference Scale previously administered to student pharmacists. Construct validity was assessed using Rasch analysis. Unidimensionality was measured using: point-biserial measure correlations; percent of raw variance explained by items; difference between expected; variance modeled by items; and Rasch model fit. To assess scale functioning, response frequency distribution, observed average and sample expected logit distribution, Andrich logit distribution, item separation, and item reliability were assessed. Visual examination of the Item-Person Map determined content validity. Items explained 64.2% of data raw variance. The difference between raw variance modeled and observed was 0.6. Point-biserial measure correlations were >0.77. Item mean-square infits were 0.7-1.3 while outfit measures were 0.72-1.16. There were >10 responses per response category, response frequency and Andrich thresholds progressively advanced, and observed average and sample expected logits advanced monotonically, Andrich logits = -2.33-1.69, item separation = 2.61, and item reliability = 0.87. Item probability curves indicated response categories were minimally yet adequately distinct. Cronbach's alpha = 0.93. The Item-Person Map had a ceiling effect indicating content gaps. In conclusion, the pain interference instrument has acceptable construct validity yet contains content gaps. Additional difficult items should be added to the instrument to better capture pain interference among student pharmacists.
Keywords: chronic pain; pain interference; patient-reported outcomes; physical functioning; quality-of-life measurement; quality-of-life outcomes; student pharmacists; validity studies.