Incentives for healthcare providers may also affect non-targeted patients. These spillover effects have important implications for the full impact and evaluation of incentive schemes. However, there are few studies on the extent of such spillovers in health care. We investigated whether incentives to perform surgical procedures as daycases affected whether other elective procedures in the same specialties were also treated as daycases.

8,505,754 patients treated for 92 non-targeted procedures in 127 hospital trusts in England between April and March 2016.

Interrupted time series analysis of the probability of being treated as a daycase for non-targeted patients treated in six specialties where targeted patients were also treated and three specialties where they were not.

The daycase rate initially increased (1.04 percentage points, SE: 0.30) for patients undergoing a non-targeted procedure in incentivised specialties but then reduced over time. Conversely, the daycase rate gradually decreased over time for patients treated in a non-incentivised specialty.

Spillovers from financial incentives have variable effects over different activities and over time. Policymakers and researchers should consider the possibility of spillovers in the design and evaluation of incentive schemes.