Rescoring the NIH chronic prostatitis symptom index: nothing new

The National Institutes of Health-chronic prostatitis symptom index (NIH-CPSI) is a commonly used 13-item questionnaire for the assessment of symptom severity in men with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS). For each item, score ranges are 0-1 (6 items), 0-3 (2 items), 0-5 (3 items), 0-6 (1 item) and 0-10 (1 item). This scoring system is straightforward, but items with wider score ranges are de facto weighted more, which could adversely affect the performance characteristics of the questionnaire. We rescored the NIH-CPSI so that equal weights were assigned to each item, and compared the performance of the standard and rescored questionnaires using the original validation dataset. Both the original and revised versions of the scoring algorithm discriminated similarly among groups of men with CP (n=151), benign prostatic hyperplasia (n=149) and controls (n=134). The internal consistency of the questionnaire was slightly better with the revised scoring, but values with the standard scoring were sufficiently high (Cronbach's >or=0.80). We conclude that although the rescored NIH-CPSI provides better face validity than the standard scoring algorithm, it requires additional calculation efforts and yields only marginal improvements in performance.