Long-term probabilistic forecasts of activity mitigation in English hospitals: a national elicitation exercise providing an outside view based on judgements of experts in support of the New Hospital Programme.

Objectives: The planning process for a new hospital relies on assumptions about future levels of demand. Typically, such assumptions are characterised by point estimates, the flaw-of-averages, base-rate neglect and overoptimism from an inside view. To counteract these limitations, we elicited an outside view of probabilistic forecasts based on judgements of experts about the extent to which various types of hospital activity might be mitigated over 20 years, in support of the New Hospital Programme (NHP) in the English National Health Service.