Segmented regression analysis*
| Variable | Estimate (95% CI) |
|---|---|
| Baseline adjustment variables | |
| Mean age | 0.01 (−0.47 to 0.49) |
| Mean CCI score | −0.52 (−4.19 to 3.15) |
| Mean SSII score | 0.28 (−0.02 to 0.58) |
| % change in SSI incidence rate per year | |
| Region A | −0.32 (−0.82 to 0.19) |
| Region B | −1.32 (−1.95 to −0.69) |
| Region C | −0.27 (−0.81 to 0.26) |
| % change in SSI incidence rate per year between regions† | |
| Region B v. region A | −1.00 (−1.40 to −0.61) |
| Region C v. region A | 0.04 (−0.14 to 0.23) |
| Region B v. region C | 1.05 (0.71 to 1.38) |
| Absolute % change in SSI incidence rate per year between regions | |
| Region A v. region B | 5.01 (3.05 to 6.97) |
| Region A v. region C | −3.36 (−4.67 to −2.04) |
| Region B v. region C | −8.37 (−11.03 to −5.70) |
CI = confidence interval; CCI = Charlson Comorbidity Index; SSI = surgical site infection; SSII = Spine Surgery Invasiveness Index.
↵* Segmented regression model adjusted for increase in mean age, mean CCI score and mean SSII score over the study period.
↵† Region A: prerollout period (Jan. 1, 2006, to Dec. 31, 2010); region B: rollout period (Jan. 1, 2011, to Dec. 31, 2014); region C, postrollout period (Jan. 1, 2015, to Dec. 31, 2019).