Unintended consequences of the 18-week referral to treatment standard in NHS England: a threshold analysis

OBJECTIVE: In 2012, an '18-week referral to treatment standard' was introduced in England. Among people on the list of those waiting for hospital treatment at a point in time, the standard states that at least '92% of patients should have been waiting for less than 18 weeks'. Targets can have unintended consequences, where patients are prioritised based on the target rather than clinical need. Such an effect will be evident as a spike in the number of hospital trusts at the target threshold, referred to as a threshold effect. This study examines for threshold effects across all non-specialist acute NHS England hospital trusts by financial year.

METHODS: A retrospective observational study of publicly available data examined waiting times for patients on the waiting list. We examined trust performance against the 92% target by financial year, from 2015/16 to 2021/22, using Cattaneo et al's manipulation density test (test for discontinuity/spike in data around target threshold) for all patients and by type of treatment.

RESULTS: The proportion of NHS hospital trusts meeting the 92% target deteriorated over time. From 2015/16 to 2019/20, there was strong evidence of a threshold effect at the 92% target (p<0.001). There was no evidence of a threshold effect in 2020/21 (p=0.063) or 2021/22 (p=0.090). Threshold effects were present across most types of treatment in 2016/17 and fewer types from 2017/18 onwards.

CONCLUSION: We observed striking evidence of a threshold effect suggesting that while targets change behaviour, they do so in a selective way, focusing on the threshold rather than a pervasive improvement in practice. However, at the height of the pandemic, as almost no trusts could reach the target, the threshold effect disappeared.