Figure 3: Opioid overdose identified by risk subgroup in the 2017–18 Pennsylvania (n=318 585) and 2015–17 Arizona Medicaid (n=391 959) external validation datasets using GBM.

Based on the individual’s predicted probability of an opioid overdose (fatal or non-fatal) event, we classified beneficiaries in the two validation datasets into risk subgroups using the modified decile thresholds of the risk scores derived from the 2013–16 Pennsylvania training dataset, with the highest risk decile further split into three additional strata based on the top first, second–fifth, and sixth–tenth percentiles to allow closer examination of beneficiaries at highest risk of experiencing an overdose. The thresholds of the risk scores derived from the 2013–16 Pennsylvania training dataset to identify a beneficiary’s risk subgroup are: top first percentile (≥98·3); second–fifth percentile (96·6≤risk score<98·3); sixth–tenth percentile (64·9≤risk score<96·6); decile 2 (47·6≤risk score<64·9); decile 3 (38·4≤risk score<47·6); decile 4 (32·2≤risk score<38·4); decile 5 (27·5≤risk score<32·2); decile 6 (23·8≤risk score<27·5); decile 7 (20·4≤risk score<23·8); decile 8 (18·8≤risk score<20·4); decile 9 (14·2≤risk score<18·8); decile 10 (14·2<risk score). GBM=gradient boosting machine.