The number of patient deaths (mortality) in a hospital is shown as a mortality ratio that compares patients' actual mortality rates to their expected rate of mortality.
The "observed-to-expected mortality" rate is a risk-adjusted measure of a hospital's mortality rate. This ratio is created from two sets of numbers:
- Observed mortality. The actual number of patients that died in the hospital each month.
- Expected mortality. The expected average of hospitalized patient deaths with a particular illness or condition that are beyond the control of the medical center, such as age, gender and other medical problems.
Observed mortality is divided by the expected mortality to create the O/E ratio.
The meaning of an O/E ratio depends on the score.
- Equal to 1.5. The hospital's mortality rate is higher than expected.
- Equal to 1.0. The hospital's mortality rate is equal to what is expected.
- Equal to 0.75. The hospital's mortality rate is 25 percent lower than expected.
- Equal to 0.50. The hospital's mortality rate is 50 percent lower than expected.
A lower score is better. Mayo Clinic has a target of 0.71.