Table 1.
Completeness of potential linkage variables in maternal and baby HES records for 2012/13.
Fig 1.
Extract flow-diagram for delivery and birth episodes captured in HES for 2012/13.
Table 2.
Probabilistic match weights.
Fig 2.
Estimated false-match rate and sensitivity for a range of threshold weights, based on synthetic data.
Table 3.
Probability of achieving a deterministic link according to completeness of baby records.
The final row shows an increase in accuracy of variables over time: in 2001/02, deterministic links were found for 73.0% of baby records with complete values on all linkage variables compared with 77.5% in 2012/13.
Fig 3.
Contribution of each linking variable to overall match weight.
Agreement = positive contribution (solid line), disagreement = negative contribution (dashed line). The higher the value, the more information the linkage variable provides.
Table 4.
Comparison of linked and unlinked baby record characteristics for 2012/13.
Missing values are excluded from all categories.
Fig 4.
Distribution of birth weight by week of gestation in baby records.
Vertical lines show 3 standard deviations from the average; values above the upper limit are likely to have been miscoded as days (rather than weeks) of gestation, truncated to 2 digits.
Fig 5.
Representativeness of linked HES cohort in terms of maternal age, birth weight and gestational age.
Dark shade = HES, light shade = Office for National Statistics.