All analyses were conducted pooling patients in both arms of the clinical trial. Descriptive statistics were used to describe patients included in the study. Continuous variables are reported as medians and interquartile ranges and categorical variables as proportions. Correlations were measured using Spearman correlation coefficients (rho). Except where noted, only data for patients who completed the week 12 study visit were analyzed; this allowed for greater variation in disease activity than at baseline, since at randomization all patients were required to have DAI scores between 4 and 10, inclusive.
To assess sensitivity and specificity for clinical remission and clinical response, we relied on the patient’s assessment of disease activity in the preceding 24 hours at randomization and at the week 12 visit. Clinical remission was defined as a self-assessment of perfect or very good (minimal disease activity). Clinical response required improvement by at least two points on the 6 point Likert scale. Receiver operating characteristics (ROC) curves were generated and the C-statistic was calculated as a summary measure of the discriminative properties of the indices. Optimal cut points were identified by the highest sensitivity × specificity product. Area under the ROC curves for different disease indices were compared using the roccomp command in Stata v10 (Stata Corp, College Station, TX).
Because neither the patient rating nor the Mayo score are a pure gold standard for disease activity, we also calculated kappa statistics across a range of cut points to assess the impact of changing cut points on the agreement between the patient ratings and partial Mayo score. The kappa statistic measures the degree of agreement between the two measures beyond that which would be expected by chance. The kappa statistic can have values ranging from −1 to 1, with values of .41–.60 representing moderate agreement, .61–.80 representing substantial agreement, and values greater than .80 representing almost perfect agreement.11 (link)
Finally, because the physician’s global assessment is likely greatly driven by the patient’s report of bowel movement frequency and bleeding, we examined whether a score composed exclusively of these two factors would perform as well as the modified DAI. This six-point scale was compared to the patient’s self report in the same manner described for the full and partial Mayo scores. We refer to this as the “6 point scale” in this report.
To assess sensitivity and specificity for clinical remission and clinical response, we relied on the patient’s assessment of disease activity in the preceding 24 hours at randomization and at the week 12 visit. Clinical remission was defined as a self-assessment of perfect or very good (minimal disease activity). Clinical response required improvement by at least two points on the 6 point Likert scale. Receiver operating characteristics (ROC) curves were generated and the C-statistic was calculated as a summary measure of the discriminative properties of the indices. Optimal cut points were identified by the highest sensitivity × specificity product. Area under the ROC curves for different disease indices were compared using the roccomp command in Stata v10 (Stata Corp, College Station, TX).
Because neither the patient rating nor the Mayo score are a pure gold standard for disease activity, we also calculated kappa statistics across a range of cut points to assess the impact of changing cut points on the agreement between the patient ratings and partial Mayo score. The kappa statistic measures the degree of agreement between the two measures beyond that which would be expected by chance. The kappa statistic can have values ranging from −1 to 1, with values of .41–.60 representing moderate agreement, .61–.80 representing substantial agreement, and values greater than .80 representing almost perfect agreement.11 (link)
Finally, because the physician’s global assessment is likely greatly driven by the patient’s report of bowel movement frequency and bleeding, we examined whether a score composed exclusively of these two factors would perform as well as the modified DAI. This six-point scale was compared to the patient’s self report in the same manner described for the full and partial Mayo scores. We refer to this as the “6 point scale” in this report.
