Sample size is determined by available resources. 240 patients randomised to the MMHU unit over 24 months, and an equal number of controls, should be sufficient to measure, with 80% power, a 3 to 6-day reduction in length of stay, and 15% increase in the proportion of participants discharged home (e.g. 50% to 65%). Power will be greater for scaled outcomes, and the 'days at home' outcome.