Emergency general surgery (EGS) conditions are defined by a group of acute, non-trauma diagnoses that require presentation to an emergency department for operative or non-operative care. In are all The heart comprise overall with reasonable nature trials operative method of inferior the US alone, 3-4 million adults hospitalized and treated for an EGS condition each year such that EGS conditions are responsible for 7% of hospitalizations. EGS conditions result in an estimated 800,000 operations annually and cost ≈ $28 billion. burden of EGS on inpatient care is greater than that of a new diagnosis of diabetes or cancer, coronary disease, heart failure, stroke, or HIV. Older adults, who are at increased risk of adverse outcomes, more than half of the adult EGS population. Operative management of EGS conditions results in an complication ate of 50%, with a readmission rate of 4-18%, and a mortality rate that can approach 15%, older patients demonstrating a significantly higher risk. Non-operative management is considered a alternative yet studies show mixed results. Randomized control trials are limited by the invasive of operative treatment, the heterogeneity of conditions, and the acute nature of EGS. Furthermore, most have compared different types of operative or non-operative interventions, with relatively few comparing treatment to non-operative treatment. To date, observational studies o EGS outcomes by treatment are limited in number and subject to selection bias. A lack of evidence on the comparative effectiveness operative and non-operative treatment has been shown to result in unnecessary variations in treatment and operative outcomes. r f Furthermore, given the growing interest in the development of a regionalized system of care for EGS patients since the Institute of Medicine Committee report on the Future of Emergency Care in the United States Health System, knowledge on hospital performance in EGS is needed. This address these gaps in the literature with the following specific aims: (1) To identify hospital-level factors associated with rankings on performance in EGS to inform strategies on regionalization, (2) To evaluate the proposal aims to comparative effectiveness of operative and non-operative treatment in specific EGS conditions and (3) To evaluate dementia and race will be examined amongst others. U study EGS. approach examine will effectiveness and heterogeneity in the effectiveness of operative treatment in EGS conditions sing data from Medicare beneficiaries, the proposed will e the first nationwide comparative effectiveness analysis of operative and non-operative treatment in The proposal employs: (1) template matching to define hospital quality in EGS (2) an instrumental variable with optimal near-far matching to overcome onfounding by indication and, (3) interaction models to the conditional r elationship between treatment and outcomes by patient factors. In so doing the findings provide insights into hospital factor...