Did paying drugs misuse treatment providers for outcomes lead to unintended consequences for hospital admissions? Difference-in-differences analysis of a pay-for-performance scheme in England

Aims To estimate how a scheme to pay substance misuse treatment service providers according to treatment outcomes affected hospital admissions. Design A controlled, quasi-experimental (difference-in-differences) observational study using negative binomial regression. Setting Hospitals in all 149 organisational areas in England for the period 2009-2010 to 2015-2016. Participants 572 545 patients admitted to hospital with a diagnosis indicating drug misuse, defined based on International Classification of Diseases 10th Revision (ICD-10) diagnosis codes (37 964 patients in 8 intervention areas and 534 581 in 141 comparison areas). Intervention and comparators Linkage of provider payments to recovery outcome indicators in 8 intervention organisational areas compared with all 141 comparison organisational areas in England. Outcome indicators included: abstinence from presenting substance, abstinent completion of treatment and non-re-presentation to treatment in the 12 months following completion. Measurements Annual counts of hospital admissions, emergency admissions and admissions including a diagnosis indicating drugs misuse. Covariates included age, sex, ethnic origin and deprivation. Findings For 37 245 patients in the intervention areas, annual emergency admissions were 1.073 times higher during the operation of the scheme compared with non-intervention areas (95% CI = 1.049; 1.097). There were an estimated additional 3 352 emergency admissions in intervention areas during the scheme. These findings were robust to a range of secondary analyses. Conclusion A programme in England from 2012 to 2014 to pay substance misuse treatment service providers according to treatment outcomes appeared to increase emergency hospital admissions.