Infant Mortality
Infant Mortality data are generated from the ONS Statistical Infant Mortality System. Since 1975, ONS has been producing an infant mortality file which links information from the death records of children who were under the age of one at time of death to the corresponding birth record. Since 1993, the age limit has been gradually changed to include children under 16 years, but results here published include only infant deaths (i.e. under one year old).
The infant mortality linked file, compiled centrally for all infant deaths in England & Wales (E&W), is searched annually for children of mothers who were born on an LS date. The extract is then matched to the annual file of Live Births to Sample Mothers. If a correspondent record is found, the infant death is then linked into the study.
Methods
The LS includes linked census and events data for people born on one of four selected dates in a calendar year. As such, the LS samples 4/365 of people born in non leap years and 4/366 of people born in leap years. This represents approximately 4/365.25 of the population resident in England and Wales in any given year. The number of expected infant deaths for LS mothers in any calendar year will be given by FIGURE 1.
In census years, the formula uses the estimated numbers of England and Wales infant deaths from the start of the year up to the day before census night (pre-census) and from the day after Census night until the end of the year (post-census). This allows to derive one pre and one post-census estimate of expected LS infant deaths.
Results
Total numbers of infant deaths to LS mothers after the 2001 Census are shown in Table 5 together with the relevant sampling fractions and linkage rates.
Table 5. Infant mortality by year of infant’s death, 2001-2005
| Year of death | LS | E&W | Sampling
fraction |
Exp. in LS | Linkage
rate |
| Part 2001 | 24 | 2,138 | 1.12 | 23 | 102.50 |
| 2002 | 29 | 3,079 | 0.94 | 34 | 86.00 |
| 2003 | 35 | 3,243 | 1.08 | 36 | 98.55 |
| 2004 | 29 | 3,158 | 0.92 | 35 | 83.85 |
| 2005 | 32 | 3,208 | 1.00 | 35 | 91.08 |
| Total | 149 | 14,826 | 1.00 | 162 | 91.77 |
Sampling fractions and linkage rates would suggest a tendency to undersampling infant deaths in the LS. However, actual and expected numbers of infant deaths are very small and are therefore more sensitive to sampling variability.
Sampling fractions and linkage rates for infant mortality since 1976 are available from the downloads section.
