Alternatives to standardised mortality ratios needed, study suggests

Standardised mortality ratios for hospitals do not provide an accurate indication of how many deaths could have been avoided, according to a study.

Researchers at the London School of Hygiene & Tropical Medicine (LSHTM) and Imperial College London say the widely used hospital-wide standardised mortality ratios (SMRs), such as the Hospital Standardised Mortality Ratio (HSMR) and Summary Hospital-level Mortality Indicator (SHMI), should not be used to benchmark hospitals’ quality of care.

SMRs compare the number of deaths in a hospital with the expected number (based on statistical probability). Such measures have been widely used in many countries for more than 20 years and are often used to identify ‘problem’ hospitals.

The study was commissioned by NHS England medical director Sir Bruce Keogh following his review of 14 NHS trusts in 2013, which questioned whether SMRs for hospitals provide an accurate indication of the number of avoidable deaths occurring.

The research, funded by the National Institute for Health Research and the Department of Health, has been published in The BMJ.

The study looked at 3,400 deaths in 34 hospital trusts in England. Experienced doctors reviewed patients’ case notes and the proportion of deaths they judged likely to have been avoidable was compared with the trust’s HSMR and SHMI. Avoidable deaths were those judged to have at least 50% likelihood of having been avoidable.

The researchers found that the proportion of avoidable hospital deaths was 3.6%. There was no significant association between hospital-wide SMRs and the proportion of avoidable deaths in a trust.

Lead author and LSHTM senior lecturer in public health Helen Hogan said: ‘Our findings suggest that the commonly used hospital-wide SMRs are not a useful reflection of the proportion of avoidable deaths in a trust.

‘Dreadful though each avoidable hospital death is, they are too infrequent to be the basis of a robust indicator to detect significant differences between trusts. There are credible alternatives for assessing the quality of hospitals which give a fairer and more accurate picture.’

Imperial College London’s Patient Safety and Translational Research Centre director and Institute of Global Health Innovation chair Ara Darzi, co-author of the study, said: 'Quality must remain the organising principle of our national healthcare system. We know that the measurement of patient safety within a hospital or clinical environment can be a useful benchmark for assessing quality in health care and our study highlights the importance of clinician-led case-note reviews as a robust and invaluable methodology for determining such quality.’

The authors recommend that staff continue to review individual deaths to identify local problems with care, but say reviewing should be standardised so that all acute hospital trusts adopt a rigorous approach and take action to prevent future deaths. They suggest SMRs should only be used to assess the quality of care for those conditions with high case fatality, such as patients in critical care, as good quality clinical data is available.

LSHTM professor of health services research and senior author of the study Nick Black said: ‘Hospital-wide SMRs can be distracting and potentially misleading, and should not be used as a basis to praise or condemn a hospital or trust. We need to support and help hospitals to raise standards, not criticise and punish them.

‘Given the complexity of hospitals, with many different clinical departments and activities, it is more helpful for the public, patients, staff and politicians to use a variety of specific measures of quality, such as adherence to good practice guidelines; outcomes for specific diseases or procedures; patient surveys of their experiences; infection rates; and staff surveys.’

Read the study's full findings here.