Data were obtained from the English Department of
Health’s hospital episode statistics database. This
database holds a standard dataset6 for English residents
treated in National Health Service hospitals since the
1987-8 financial year. The first year’s data was not con-
sidered as complete as in later years. In 1988-9 opera-
tion codes were coded by Version 3 of the Office of
Population Censuses and Surveys Classification of Sur-
gical Operations’, which makes them difficult to com-
pare with later years which were coded using version 48.
This study therefore considers the financial years
1989-90 to 1995-6, with the years running from 1 April
to 31 March.