Extent of between-practice variation explained by each model expressed as percentage reduction in random-effects variance and by median incidence rate ratio
| Model | Random-effects variancea | Percentage reduction in variance | MIRRb | Ratio of MIRR to that of null model |
|---|---|---|---|---|
| Null (random effect only) | 0.58 | — | 2.07 | — |
| Population characteristics only | 0.50 | 16.4 | 1.95 | 0.95 |
| Practice characteristics only | 0.56 | 2.8 | 2.05 | 0.99 |
| Both population and practice characteristics | 0.49 | 17.9 | 1.95 | 0.94 |
↵a This is the variance between practices measured on the log-scale.
↵b This is the ratio of the CXR rate for a practice at the 75 th centile of the CXR utilisation against the CXR rate for a practice at the 25 th centile of CXR utilisation, estimated using the random-effects variance. CXR = chest X-ray. MIRR = median incidence rate ratio.