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Introduction: Reports on hospital-specific, risk-standardized outcomes using claims data on acute ischemic stroke are increasing. However, these reports sometimes fail to account for stroke severity.Hypothesis: Hospital-specific, risk-adjusted mortality rating without accounting for stroke severity are altered after including initial severity for ischemic strokes.Methods: The health insurance claims data known as the Japanese Diagnosis Procedure Combination/Per Diem Payment Systems between April 1, 2013 and May 31, 2014 was obtained from 332 certified training institutions in Japan. The hospital-specific, risk-adjusted 30-day mortality rate was calculated using a hierarchical logistic regression model. We developed two models, with and without initial levels of consciousness (LOC), and compared them to assess the impact of stroke severities on hospital-specific mortalities. The hospital-specific mortalities with and without LOC were ranked and groped into 3 categories (top 20%, middle 60%, and bottom 20%), and then compared across the two models. We used an integrated discrimination improvement (IDI) index to measure how the model with LOC reclassified patients compared with the model without LOC. Patients with deep comas were excluded from the analyses.Results: We analyzed 64,569 acute ischemic stroke patients. Crude 30-day mortality was 3.9% , the mean age was 74.1±1.3 years, 41.2% were women, 70.8% had hypertension, 29.2% had diabetes mellitus, 79.9% had a Charlson comorbidity index score greater than 5, 3.7% had severe LOC (coma/semi-coma) and 8.1% had modestly impaired LOC. Among hospitals ranked in the top 20% of performers without LOC, 26.9% were ranked in the middle 60% when LOC was adjusted. Among the bottom 20% of performers without LOC, 21.2% were ranked in the middle 60% when LOC was adjusted. The hospital-specific, risk-adjusted 30-days mortality model with LOC had a significantly better IDI index score than the model without LOC (IDI, 0.09; P<0.001).Conclusions: Adding the metric of stroke severity to a hospital-specific, risk-adjusted 30-day mortality model based on claims data was associated with model improvement and changes of mortality-based performance rankings.