Update to the methodology used to calculate health expectancies.
Background
The Office for National Statistics (ONS) will adopt the Integrated Household Survey (IHS), encompassing the Annual Population Survey, as the primary survey data source for the calculation of health expectancies for the UK and constituent countries from 2013. This article reports the likely impact of this change along with an assessment of different models of imputation to counter the loss of general health and limiting persistent illness data for children from the underlying survey source.
Methods
In the first instance, general health rates reported in the IHS were compared with those reported in the General Lifestyle Survey (GLF) and Continuous Household Survey (CHS)/Health Survey for Northern Ireland (HSNI) over the same period. Assessment was then made of the likely impact of change to the age-band structure of health expectancy (HE) calculations, reflecting the lack of data for children in the IHS. Finally, three methods of imputation of child health data were compared to age-band revised estimates of HE in order to assess which approach gave the greatest continuity with the ONS HE series.
Results
The prevalence of general health reported in the IHS was on the whole similar to that reported in other survey sources. Estimates of ‘Very good' and ‘Good' general health were slightly lower in the IHS compared to the GLF and CHS/HSNI for the UK, GB and England, but slightly higher for males in Scotland and all persons in Northern Ireland. The effect of changing the age categorisation in the calculation of healthy life expectancy was negligible; but led to small increases in disability-free life expectancy. Using the prevalence of health states at age 16-19 as a direct proxy for health states in younger age-bands gave results that were most consistent with ONS' historic time series of health expectancies.
Conclusions
Adoption of the IHS will lead to a relatively minor discontinuity in ONS health expectancy series. The impact of small differences in health state reporting of adults in the IHS compared to the GLF/ CHS/ HSNI is likely to be negligible. Changing the underlying age categorisation to improve the accuracy of ONS estimates of health expectancies and imputing the health status of children will have a larger effect but is likely to result in a discontinuity of less than one year at birth.
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