Table 2:

Results from ARIMA models using 6 years of data among clients in safer opioid supply program and the matched unexposed group

OutcomeGroupModel*Step estimate (95% CI) (rate)Step function (p value)
Primary analysis
Rate of ED visitsSafer supply(0, 1 12, 1)−13.9 (−25.6 to −2.1)0.02
Matched unexposed(0, 1 12, 1)−2.0 (−6.3 to 2.3)0.4
Rate of hospital admissionsSafer supply(0, 1 12, 1)−5.2 (−8.7 to −1.7)0.005
Matched unexposed(0, 1 12, 1)0.6 (−1.1 to 2.4)0.5
Rate of admission for infectionSafer supply(0, 1 12, 1)−1.6 (−4.0 to 0.8)0.2
Matched unexposed(0, 1 12, 1)0.1 (−0.9 to 1.2)0.8
Health care costs§Safer supply(0, 1 12, 2)−922 (−1577 to −268)0.008
Matched unexposed(2, 1 12, 0)−73 (−365 to 219)0.6
Sensitivity cohort matched on HIV diagnosis
Rate of ED visitsSafer supply(0, 1, 1)−9.1 (−17.6 to −0.6)0.03
Matched unexposed(0, 1, 1)−3.8 (−7.8 to 0.2)0.06
Rate of hospital admissionsSafer supply(0, 1, 1)−4.3 (−7.6 to −1.0)0.01
Matched unexposed(0, 1, 1)−0.9 (−2.3 to 0.6)0.2
Rate of admission for infectionSafer supply(0, 1, 1)−1.1 (−2.7 to 0.6)0.2
Matched unexposed(2, 1, 0)0.4 (−0.7 to 1.4)0.5
Health care costs§Safer supply(6, 1, 0)−668 (−1209 to −126)0.02
Matched unexposed(4, 1, 0)29 (−309 to 367)0.9
• Note: ARIMA = autoregressive integrated moving average, CI = confidence interval, ED = emergency department.

• * Model specification represented as (p, d, q): p is the number of lags of the dependent variable, representing the autoregressive nature of the model; d represents the number of times the data have to be differenced to ensure stationarity, and “1 12” represents seasonal differencing; q is the number of lags for the error term, representing the moving average part of the model.

• Rate reported per 100 individuals for all outcomes except health care costs, which are reported per person. Parameter estimate indicating the level change in the rate of each outcome as estimated by the ARIMA model. For example, a step estimate of −13.9 in the first row indicates a reduction in the monthly rate of ED visits of 13.9 visits per 100 individuals after entry into the safer opioid supply program.

• p value corresponding to the parameter estimate indicating the level change in the rate of each outcome as estimated by the ARIMA model.

• § Excluding primary care costs.