Psychiatric and substance abuse disorder diagnoses as predictors of length of hospital stay.

The mental health and substance abuse components of AN-DRG 3 were examined using data from all inpatient separations in two Australian States over a two-year period. Assignment to a mental health or a substance abuse diagnosis related group (DRG) predicted about 20 per cent of the variability in average length of stay of patients treated for such conditions. Assignment to a substance abuse DRG was a much less robust predictor of length of hospital stay than assignment to a mental health DRG. There was little variation between years or States. Day-only intent patients were excluded, as were long-stay outliers identified using an inter-quartile range trimming process. Psychiatric DRGs are similar to a number of other non-surgically focused diagnosis related groups in their capacity to predict length of hospital stay. They are likely to remain an important component of casemix classification systems.