Change in the monthly PPI dispensing counts, rate of switching to a lower strength PPIs and rates of treatment discontinuation at each intervention point, estimated using ARIMA models adjusted for seasonality
| Seasonal ARIMA model specification* | Mean monthly dispensings† | Level shift‡ from April 2015 | Level shift from May 2016 | |
| % (95% CI) | % (95% CI) | |||
| Dispensing counts | ||||
| PPIs | (2,1,0) (0,1,0)12 | 164 361 | 0.6 (−0.7 to 2.0) | −1.7 (−2.9 to −0.4) |
| High strength | (1,1,0) (0,1,0)12 | 28 728 | −0.2 (−3.1 to 2.7) | 0.3 (−2.6 to 3.3) |
| Standard strength | (0,1,1) (0,1,0)12 | 128 156 | 1.2 (0.1 to 2.3) | −1.7 (−2.7 to −0.7) |
| Low strength | (0,1,1) (0,1,0)12 | 7481 | −0.1 (−2.6 to 2.5) | −0.8 (−2.9 to 1.4) |
| Statins (control) | (0,1,1) (0,1,1)12 | 187 407 | 1.0 (−1.1 to 3.3) | −1.6 (−3.7 to 0.5) |
| Switching to lower strength PPI | ||||
| (0,1,1) (1,0,0)12 | 3.0 (−1.6 to 7.7) | 0.2 (−3.8 to 4.4) | ||
| Treatment discontinuation | ||||
| PPIs | (2,1,0 1,1,0)12 | −0.1 (−0.4 to 0.2) | −0.1 (−0.4 to 0.2) | |
| Statins (control) | (1,0,0) (0,1,0)12 | 0 (−0.3 to 0.4) | 0.3 (0 to 0.6) | |
*ARIMA (p,d,q) x (P,D,Q)12 model where 12 indicates seasonal differencing at 12-month lag.
†Mean monthly dispensings in the year leading up to NPS MedicineWise programme in April 2015.
‡A sudden, sustained change for the remainder of the study period.
ARIMA, autoregressive integrated moving average;PPI, proton pump inhibitor.