Length of stay of acute psychiatric inpatients: an exponential model.

We examined the length of stay of inpatients admitted to a psychiatric unit in central London. The commonest length of stay (mode) was less than 1 week. In general, subsequent weeks showed successively fewer discharges, so that the distribution curve of the number of patients by length of stay showed a smooth decline. Analyzing the first 13 weeks of stay, the distribution curve corresponded very closely to a theoretical exponential decay curve. This has implications for recording the average length of stay and thus for comparing one hospital unit with another. It may also have implications for planning for acute psychiatric services. A plea is made for using the median rather than the mean for recording the average length of admission for some purposes.