Results for DiD analysis (%)
| Model 1 (standard DiD) | Model 2 (standard DiD) | Model 3 (high cost procedures) | Model 4 (low cost procedures) | Model 5 (time trend analysis) | Model 6 (combination) | |
| Phase I | 0.54*** (0.53 to 0.56) | 0.55*** (0.54 to 0.57) | 0.92*** (0.89 to 0.94) | 0.92*** (0.89 to 0.94) | 0.53*** (0.52 to 0.54) | 0.54*** (0.52 to 0.55) |
| EBI | −11.82*** (−12.89 to –10.75) | −12.50*** (−14.01 to –10.99) | −8.65*** (−10.40 to –6.90) | −11.21*** (−13.00 to –9.42) | – | −4.98** (−7.20 to –2.75) |
| EBI×phase I | 0.10*** (0.09 to 0.11) | 0.10*** (0.09 to 0.11) | 0.15*** (0.13 to 0.16) | 0.17*** (0.16 to 0.19) | – | 0.05*** (0.03 to 0.06) |
| t | – | – | – | – | −0.27*** (−0.37 to –0.16) | −0.22*** (−0.33 to –0.12) |
| t≥EBI | – | – | – | – | −0.87 (−1.15 to –0.59) | −0.36* (−0.71 to –0.02) |
| t×phase I | – | – | – | – | 0.00*** (0.00 to 0.00) | 0.00** (0.00 to 0.00) |
| t≥EBI×phase I | – | – | – | – | 0.01 (0.00 to 0.01) | 0.00 (−0.00 to 0.00) |
| Year dummies | No | Yes | Yes | Yes | Yes | Yes |
| Month dummies | No | Yes | Yes | Yes | Yes | Yes |
| Controls | No | Yes | Yes | Yes | Yes | Yes |
| Constant | 4.31*** (4.29 to 4.32) | 4.18*** (4.08 to 4.29) | 3.89*** (3.78 to 4.01) | 3.85*** (3.75 to 3.96) | 4.21*** (4.10 to 4.32) | 4.20*** (4.09 to 4.32) |
| Observations | 6750 | 6750 | 6750 | 6750 | 6750 | 6750 |
| Units of observation | 135 CCGs | 135 CCGs | 135 CCGs | 135 CCGs | 135 CCGs | 135 CCGs |
Co-efficients are reported as percentages, and can be understood as follows: phase I is the percentage difference in change in volumes between the treatment and control group. EBI is the percentage difference in volumes for all procedures before and after the implementation of the EBI programme. In models 1–4, EBI×phase I represents the treatment effect of the EBI programme and is the percentage DiD of volumes before and after implementation between the treatment and control groups. In model 6, EBI×phase I is the percentage difference in changes in volumes between the treatment and control groups during implementation of the EBI programme; t reflects monthly percentage change in volumes for all procedures; t≥EBI reflects the monthly percentage change in volumes for all procedures after the implementation of the EBI programme; t≥EBI×phase I reflects the DiD in the monthly percentage change in volumes between the treatment and control groups after the implementation of the EBI programme. 95% CIs are mentioned in parentheses. All models used fixed effects, therefore errors are clustered at the CCG level. This table was created by the coauthors of this manuscript.
*P<0.05; **p<0.01; ***p<0.001.
–, not applicable to this model; CCG, clinical commissioning group; DiD, difference-in-difference; EBI, evidence-based interventions programme.