Scaling coefficients for opioid deaths and subgroups of opioid in three periods
| 2005–2009 | 2010–2014 | 2015–2017 | ||
| All opioids | Scaling coefficient | 1.10 | 1.10 | 1.16 |
| 95% CI | 1.07 to 1.13 | 1.07 to 1.13 | 1.13 to 1.19 | |
| Prescription opioid | Scaling coefficient | 1.03 | 1.03 | 1.03 |
| 95% CI | 0.99 to 1.07 | 1.00 to 1.07 | 1 to 1.06 | |
| Heroin | Scaling coefficient | 1.07 | 1.15 | 1.20 |
| 95% CI | 1.00 to 1.13 | 1.10 to 1.2 | 1.15 to 1.25 | |
| Synthetic opioid | Scaling coefficient | 0.88 | 0.92 | 1.16 |
| 95% CI | 0.84 to 0.91 | 0.89 to 0.95 | 1.10 to 1.21 |
For the analysis by type of opioid, that is, prescription opioid, heroin and synthetic opioid, more than one opioid can be reported in the death certificate. The number of commuting zones included in the models varies by period and by opioid type as commuting zones with zero deaths for any given outcome are dropped from the model when the outcome is log-transformed. A sensitivity analysis, including only commuting zones with at least one death involving each opioid type, resulted in the similar superlinear/sublinear scaling pattern (online supplemental table 3).