International evidence suggests that there are substantial socio-economic inequalities in the delivery of specialist health services, even in the UK and other high-income countries with publicly funded health systems (Goddard and Smith 2001, Dixon et al. 2003, Van Doorslaer, Koolman and Jones 2004, Van Doorslaer et al. 2000). Studies of total hip replacement in the English NHS have yielded particularly striking examples, given that hip replacement is such a common, effective and longestablished health technology. Administrative data show that people living in deprived areas are less likely to receive hip replacement (Chaturvedi and Ben-Shlomo 1995, Dixon et al. 2004) while survey data suggest they may be more likely to need it (Milner et al. 2004). However, previous studies have not examined change in inequality over time. This paper presents evidence on the change in socio-economic inequality in small area use of elective total hip replacement in the English NHS, comparing 1991 with 2001. This was a period of important large-scale health care reform in England, involving at least two significant reforms that might potentially have influenced socio-economic inequality in health care delivery: (1) the introduction and subsequent abolition of the Conservative “internal market” 1991-7, and (2) the introduction in 1995 of a revised NHS resource allocation formula designed to reduce geographical inequalities in health care delivery. Two datasets, for 1991 and 2001, were assembled from routine NHS data sources: Hospital Episode Statistics (HES) on hospital utilisation in England and the corresponding decennial National Censuses in 1991 and 2001. Both datasets contain information on over 8,000 electoral wards in England (over 95% of the total). To improve comparability, a common geography of frozen 1991 wards was adopted. The Townsend deprivation score was employed as an indicator of socio-economic status. Inequality was analysed in two ways. First, for comparability with previous small area studies of hip replacement, by using simple range measures based on indirectly age-sex standardised utilisation ratios (SURs) by deprivation quintile groups. Second, using concentration indices of deprivationrelated inequality in use based on indirectly age-sex standardised utilisation ratios for each individual small area. Each SUR is the observed use divided by the expected use, if each age and sex group in the study population had the same rates of use as the national population.
