The study by Chan et al. used a three-step LMW clustering procedure to identify OD subgroups in a sample of 4,061 subjects, all of which were included in the present study (Chan et al., 2011). To differentiate whether the results reported here differed from those of Chan et al. due to the larger sample in the current study or the different analytic approach employed, we applied the LMW approach of Chan et al. to the full sample of 5,390 subjects. This also resulted in 5 clusters. Table 5 cross-tabulates Groups A to E from the LMW analysis with Groups 1–5 derived using our analytic method. The moderate opioid user Group B and the heavy late-onset user Group C resulting from the LMW method (estimated heritability = 0.70 and 0.60) comprised only 449 and 88 individuals, respectively, and the estimated heritability of all other groups was below 0.50. The groups that had an early-onset of OD (i.e., highly comorbid and heavy opioid users) largely overlapped in Group E and Group 5. However, the disagreement of the cluster labels assigned to the
