The codes for the different types of hospital are L (large), S (small), DC (diagnosis centre) and TC (treatment centre). The number of patient days is calculated from the number of days that patients were in hospital. For example, a day case (a patient who was not in hospital overnight) would count as 1 patient day and a patient staying in the hospital over 3 consecutive nights would count as 4 patient days. The rate given is the rate per 100,000 patient days.