Meaningful within-patient change thresholds
migraine headache
REGRESSION, MIGRAINE HEADACHE
Anchor-based analyses were used to determine the meaningful within-patient change in WPAI domain scores. Monthly migraine headache days decreased by 50%, MSQ-RFR scores decreased by ≥ 25.71 points and MSQ-RFP scores decreased by ≤ 20 points were selected as anchors.WPAI change score threshold was estimated by logistic regression with the selected anchor as a dependent variable and change from baseline WPAI score as an independent variable. Discriminative ability between the responder and non-responder groups were assessed using receiver-operator characteristic (ROC) curves, Youden index (YI), Phi correlations, and Concordance (C) statistics, which is the equivalent of the area-under-curve (AUC) of a ROC curve.The YI, a frequently used summary measure in ROC analyses, measures the effectiveness of a predictive marker, and enables selection of an optimal threshold value for that marker. The YI was calculated at each level of improvement in the WPAI (c): [YI (c) = sensitivity (c) + (specificity (c) −1)]. Its value ranges from 0 through 1; higher value indicates better discriminative ability between the responders and non-responders. The optimal cut-score is identified as the point at which YI is maximal in the ROC analysis [