Table 4. Predictive performance of developed birth weight model with average intercept in each internal-external cross validation cycle. UK (Allen et al, 2017),32 Australia (Rumbold et al, 2006),31 and Norway (STORK Groruddalen research programme, 2010)33 cohorts, and pooled estimate.
| Pooled estimate | Allen et al, 2017 | Rumbold et al, 2006 | STORK Groruddalen, 2010 | |
| No of pregnancies for model development | — | 236 183 | 235 351 | 236 405 |
| No of pregnancies for external validation | — | 1045 | 1877 | 823 |
| Calibration slope | ||||
| Point estimate | 1.00 | 0.90 | 1.07 | 1.04 |
| Confidence interval | 0.78 to 1.23 | 0.82 to 0.97 | 1.02 to 1.12 | 0.96 to 1.12 |
| Prediction interval | −0.25 to 2.26 | — | — | — |
| τ2 (95% CI) | 0.01 (0.00 to 0.14) | — | — | — |
| Calibration-in-the-large (g) | ||||
| Point estimate | 9.72 | −22.32 | −33.42 | 86.41 |
| Confidence interval | −154.3 to 173.8 | −48.36 to 3.7 | −53.4 to −13.5 | 57.3 to 115.5 |
| Prediction interval | −943.23 to 962.67 | — | — | — |
| τ2 (95% CI) | 4200 (801 to 76000) | — | — | — |
| Observed to expected birth weight ratio | ||||
| Point estimate | 1.00 | 1.00 | 0.99 | 1.03 |
| Confidence interval | 0.94 to 1.07 | 0.95 to 1.04 | 0.94 to 1.05 | 0.97 to 1.09 |
| Prediction interval | 0.81 to 1.20 | — | — | — |
| τ2 (95% CI) | 0.00 (0.00 to 0.01) | — | — | — |
| R2* (%) | ||||
| Median | 45.7 | 32.6 | 47.4 | 45.7 |
| Range | 32.2-47.8 | 32.2-32.8 | 47.1-47.8 | 45.0-46.2 |
| interquartile range | 32.7-47.4 | 32.5-32.7 | 47.4-47.5 | 45.5-45.8 |
*
Reported as median, range, and interquartile range for imputations because R2 cannot be summarised for all imputations with Rubin’s rules.
CIconfidence interval