BackgroundUnwarranted clinical variation in hospital care includes the underuse, overuse, or misuse of services. Audit and feedback is a common strategy to reduce unwarranted variation, but its effectiveness varies widely across contexts. We aimed to identify implementation strategies, mechanisms, and contextual circumstances contributing to the impact of audit and feedback on unwarranted clinical variation.MethodsRealist study examining a state-wide value-based healthcare program implemented between 2017 and 2021 in New South Wales, Australia. Three initiatives within the program included audit and feedback to reduce unwarranted variation in inpatient care for different conditions. Multiple data sources were used to formulate the initial audit and feedback program theory: a systematic review, realist review, program document review, and informal discussions with key program stakeholders. Semi-structured interviews were then conducted with 56 participants to refute, refine, or confirm the initial program theories. Data were analysed retroductively using a context-mechanism-outcome framework for 11 transcripts which were coded into the audit and feedback program theory. The program theory was validated with three expert panels: senior health leaders (n = 19), Agency for Clinical Innovation (n = 11), and Ministry of Health (n = 21) staff.ResultsThe program’s audit and feedback implementation strategy operated through eight mechanistic processes. The strategy worked well when clinicians (1) felt ownership and buy-in, (2) could make sense of the information provided, (3) were motivated by social influence, and (4) accepted responsibility and accountability for proposed changes. The success of the strategy was constrained when the audit process led to (5) rationalising current practice instead of creating a learning opportunity, (6) perceptions of unfairness and concerns about data integrity, 7) development of improvement plans that were not followed, and (8) perceived intrusions on professional autonomy.ConclusionsAudit and feedback strategies may help reduce unwarranted clinical variation in care where there is engagement between auditors and local clinicians, meaningful audit indicators, clear improvement plans, and respect for clinical expertise. We contribute theoretical development for audit and feedback by proposing a Model for Audit and Feedback Implementation at Scale. Recommendations include limiting the number of audit indicators, involving clinical staff and local leaders in feedback, and providing opportunities for reflection.