The average costs of patient care change over time, and the way that hospitals have to code their activity into different types of healthcare work also changes each year.
So each financial year we work with the reference cost data provided by hospitals and re-calculate how many weighted activity units (WAUs) each type of clinical activity is ‘worth’.
Reference costs give us the average costs for all hospital trusts, but we only use the data for acute (non-specialist) hospital trusts.
The figure of £3,500 was chosen because it was roughly the average cost of an elective inpatient stay (where a patient is admitted to hospital for at least one night for a planned procedure), such as a single elective abdominal hernia operation, in 2014/15. Lord Carter used 2014/15 data in his report into productivity in NHS hospitals, which introduced the WAU.
Every year we adjust the constant that we use in our calculations so that £3,500 is still the average cost per WAU, and so that trusts can continue to compare their cost per WAU (productivity) to a benchmark cost of £3,500 every year. To make this work, every year the constant in our calculations varies slightly. The constant used for 2017/18 is 3516.01. The table below shows the constant for previous years.
These adjustments mean that trusts can’t make a direct comparison between cost per WAU in different financial years (for example, you cannot compare a cost per WAU of £4,000 last year to £3,900 this year and say that you have improved by £100). This is why we don't provide trendline charts for these metrics.
You can also consistently compare relative costs with your peers, and with the average cost of a WAU, to see whether you are above or below average, and how near or far from average.
Table: WAU constant for each year of reference cost data