Comparing the Early Mortality Rates of the Local Authorities in England and Wales

Abstract

Overall mortality rates of sub-populations are frequently adjusted for factors like sex and age to make them more directly comparable. In this paper we are concerned with the problem of adjusting various early infant mortality rates of the Local Authorities of England and Wales for variations in their circumstances. For example, the proportion of infants of low birth weight (which is well correlated with perinatal mortality rate) shows a strong North-South contrast, and this needs to be taken into account. The usual direct and indirect methods of adjustment are not suitable here since we intend to correct for a relatively large number of factors. Instead we employ regression analysis, the residuals in effect being the corrected mortality rates. In most regression analyses chief interest lies in the estimated model, residuals often being discarded as worthless once the fit has been judged adequate and error estimated. In this paper by contrast they are of prime importance and we go to considerable lengths to ensure that the order of merit table that they produce is robust. With a stepwise procedure to ensure that we correct only for worthwhile explanatory variables out of our list of 86, Bath and Carlisle are identified as having extremely high corrected perinatal mortality rates and Hull and Hartlepool exceptionally low. Lists of outstanding Authorities change with the mortality rate used quite strongly. In a few cases we find that Authorities with low corrected rates for one grade of mortality (late neonatal, say) have high corrected rates for another (postneonatal, for example). Explanation levels are generally high, sometimes reaching 90 per cent or more. As for important regressor variables, it is found that those describing social and economic circumstances dwarf those representing medical services for all of the mortality rates used, though to be fair, these are inadequately represented in our data set. As far as perinatal mortality rate is concerned, the proportion of low weight infants, not surprisingly, turns out to be all-important.