Transition to stable response
HDRS-17
Patients receiving chronic therapeutic SCC DBS have been observed to show a characteristic response trajectory marked by a transient period of increased behavioural reactivity and instability followed by an improvement in symptoms that is sustained and stableIn the case of HDRS-17, the relative score, which is the ratio of the aggregate score to the average of the presurgical baseline scores, was used to define the states. A threshold of 0.5, indicating a decrease of 50% from the presurgical baseline, was used to follow the widely accepted definition of clinical response. In the case of the SDC and the face classifier output, it is not clear what the exact thresholds that correspond to clinical response should be. Therefore we used the ROC curve, which focuses on sensitivity and selectivity of discriminability instead of hard thresholds, to compare against HDRS-17. However, when compared against each other, it is possible to use the same thresholds, as the values indicate the probability of being in the ‘sick’ state. We used a more conservative threshold of 0.35 to identify the transition to ‘stable response’.The concordance between the weeks of transition was evaluated using Kendall’s tau metric, which is a rank-based correlation measure. Kendall’s tau reflects the similarity in the ranks of the transition weeks, that is, do the participants who exhibit a transition in SDC early also exhibit a transition in the face early and vice versa?