Data collection
In England all NHS hospitals are organised into trusts. Each trust provides secondary and tertiary care for a geographically defined catchment population. Typically, each trust runs between one and four larger district hospitals depending on the size and spread of their catchment population and local service delivery models. HES data are collected from all NHS Trusts in England and related to episodes of hospital care provided by the NHS. The data are entered by trained data coders within each trust. We used data for the six-year period 1st January 2014 to 31st December 2019.