The Hospital Standardised Mortality Ratio (HSMR) compares the number of deaths in a hospital with the number of deaths that are predicted adjusting for a range of known risk factors. The ratio is calculated by dividing the number of observed deaths by the number of predicted deaths.
An HSMR greater than 1 (sometimes reported as a per cent ie >100), means the number of observed deaths is more than the number of predicted deaths. An HSMR less than 1 (<100) means that the number of observed deaths is fewer than the number of predicted deaths.
HSMRs can be calculated using either the number of observed deaths that occur during a patient’s hospital admission only (for example, the HSMR reported by Health Roundtable); or using the number of observed in-hospital deaths plus the number of deaths that occur within 30 days of a patient being discharged from hospital (for example, the HSMR calculated by the Ministry of Health and the Health Quality and Safety Commission). The standard set of risk factors that are used for risk adjustment are factors known to influence mortality such as age, sex, primary diagnoses, prior conditions, and the type of admission (acute or elective).
HSMRs are useful quality indicators when comparing a hospital with the national average and within a hospital over time.
Further information about HSMRs, how to interpret high and low HSMRs, and the limitations of their use can be found at the Health Quality and Safety Commission’s website [view more about HSMRs].
How are we doing?
At Waitemata DHB we track the HSMR using both Health Roundtable reports and Ministry of Health and Health Quality and Safety Commission (HQSC) reports.
Both the Health Roundtable and Ministry of Health HSMRs show that Waitemata DHB has the lowest HSMR for all District Health Boards in New Zealand. HSMRs were made publicly available in 2010/11 and 2011/12 by the Ministry of Health as part of the DHB performance framework. In September 2015 the Health Quality and Safety Commission with the Ministry of Health (MoH) published a new HSMR report [view HSMR report] , as part of a growing range of quality measures published by the Commission. The HQSC/MoH HSMR report shows the national average HSMR over a 7 year period (from 2007 to 2013), and the HSMRs for each DHB over this period. The data shows:
- The HSMR for Waitemata DHB in 2013 was 0.72, this compares with a national average for all 20 DHBs of 0.87 and is the lowest HSMR of all DHBs
- New Zealand overall has a declining HSMR over time and Waitemata DHB’s HSMR has declined over the last seven years from a high in 2009 of 0.84, to 0.72 in 2013