Hospital mortality rates refer to the percentage of patients who die while in the hospital. Mortality rates are calculated by dividing the number of deaths among hospital patients with a specific medical condition or procedure by the total number of patients admitted for that same medical condition or procedure. This risk adjustment method is used to account for the impact of individual risk factors such as age, severity of illness and other medical problems that can put some patients at greater risk of death than others.
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For example, it would be surprising if an otherwise healthy 60-year-old patient died after a hip replacement surgery, in contrast to a 93-year-old patient with multiple health problems dying after that same surgery.
To compare Mayo Clinic hospitals observed mortality rates with those of hospitals around the nation, we use a ratio calculation to standardize the measurement. This risk-adjusted mortality ratio (hospital standardized mortality ratio, or HSMR) compares a hospital's actual mortality rate with the risk-adjusted expected mortality rate.
Risk-adjusted mortality = Observed rate/risk-adjusted expected rate (x100)
To calculate the risk-adjusted expected mortality rate (the mortality rate we would expect given the risk factors of the admitted patients), statisticians use data from a large pool of patients with similar diagnoses and risk factors to calculate what the expected mortality would be for that group of patients. These data are obtained from national Medicare patient records.
At Mayo Clinic hospitals, a greater percentage of patients than average who are expected to die in the hospital, due to their individual risk factors or the seriousness of their condition, survive their hospitalization. Mayo Clinic currently has one of the lowest standardized mortality rates in the nation.