This is the fourth in a series of seven articles.

Changing technology is probably the main force driving the substitution of healthcare resources. This is because new treatments, procedures, and diagnostic techniques allow conditions to be managed in different settings by different staff. Such change is generally incremental, but occasionally new technologies fundamentally change the organisation of care. For example, the development of effective chemotherapy in the 1940s allowed tuberculosis to be managed on an outpatient basis, which led directly to the closure of nearly 30 000 hospital beds and the elimination of an entire class of hospital. Advances in primary prevention might also, in the long term, lead to a reduced need for admission to hospital. Yet such step changes are ultimately outside the hands of clinicians, managers, and policymakers, despite their intimate concern with the organisation, scale, and cost of the hospital sector. The policy debate has tended to focus on what might be described as the “appropriateness gap”—how to provide substitute care for inpatients who do not strictly need to be in hospital because of current technologies.