Risk-Adjusted Mortality Rate

Hospital mortality rates refer to the percent of patients who die while in a hospital. To calculate observed or raw mortality rates you divide 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. However, because every patient admitted to the hospital for a given condition does not have the same risk of death, observed mortality rates aren't a perfect means of comparing the quality of care delivered by different hospitals. For example, it would be surprising if an otherwise healthy 60-year-old patient died following a hip replacement surgery. In contrast, it would be less surprising if a 93-year-old patient with multiple health problems died following that same surgery.

To compare Mayo Clinic hospitals observed mortality rates to hospitals around the nation, we use a ratio calculation to standardize the measurement. This risk-adjusted mortality ratio (HSMR – Hospital Standardized Mortality Ratio) compares a hospital's actual mortality rate to the risk-adjusted expected mortality rate.

Risk-adjusted Mortality = Observed Rate/Risk-adjusted Expected Rate (X100)

It is easy to interpret:

• Equal to 100 — no difference between a hospital's mortality rate and the expected average rate

• More than 100 — hospitals mortality rate is higher than the expected average rate

• Less than 100 — hospitals mortality rate is lower than the expected average rate

How Risk-adjusted Expected Mortality Rates are Helpful

Risk-adjustment is a method used to account for the impact of individual risk factors — such as age, severity of illness(es), and other medical problems — that can put some patients at greater risk for death than others. 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.

Mortality Rates at Mayo Clinic Hospitals

Mayo Clinic processes data about all hospitalized patients on a monthly basis about 3 months after discharge. About 35 percent of patients who are expected to die in the hospital, due to their individual risk factors and/or the seriousness of their condition, survive their hospitalization. Mayo Clinic currently has one of the lowest standardized mortality rates in the nation, and this has remained steady throughout most of the past 4 years.