The quantitative validation of non-endoscopic disease activity indices in ulcerative colitis.

BACKGROUND Ulcerative colitis disease activity indices have not been formally validated. AIM To analise quantitatively the psychometric and performance validity of two non-endoscopic indices for ulcerative colitis, the Simple Clinical Colitis Activity Index and the Seo Index. METHODS In 66 patients with ulcerative colitis, the measurement of disease activity was repeated with the two non-endoscopic indices, St Mark's Index, and the Inflammatory Bowel Disease Questionnaire. Psychometric validity was evaluated by measuring the content, construct, criterion-convergent and criterion-predictive validity on a 0-1 scale. Performance validity was evaluated by measuring the reproducibility and responsiveness on a 0-1 scale. RESULTS The Simple Clinical Colitis Activity Index had good to excellent psychometric and performance validity, while the Seo Index had moderate to excellent psychometric validity and moderate to good performance validity. The Simple Clinical Colitis Activity Index had weaknesses in content validity and in responsiveness. The Seo Index had weaknesses in content validity, construct validity and responsiveness. CONCLUSIONS These two non-endoscopic indices for ulcerative colitis have good psychometric and performance validity, and are now the most rigorously validated disease activity indices for ulcerative colitis. The Simple Clinical Colitis Activity Index appears to have better overall validity. Quantitative evaluation identifies weaknesses in disease activity indices, and can lead to better disease activity indices for ulcerative colitis.