On Standardised Mortality Ratios and Preventable Deaths

Helen Hogan has summarised the problems with both Standardised Mortality Ratios (SMRs) and preventable deaths, and News Blog readers might like to read her report.[1] The signal to noise ratio with SMRs is lousy so they don’t even qualify as a screening test and would not pass the NHS screening committee – not by a wide margin.[2] Case-note review of deaths to determine preventability is fraught with difficulties relating to measurement error.[3] Neither is a good option, but if I had to choose I would go for case-note review every time. Why? Because at least it provides learning about quality of care issues. For example, we found problems with failure to use non-invasive ventilation and excessively rapid lowering of high potassium levels in our reviews of case-notes.[4] These provide real learning opportunities akin to the excellent clinical review meetings we would conduct when I was a young doctor on the medical wards.

— Richard Lilford, CLAHRC WM Director


  1. Hogan H. The problem with preventable deaths. BMJ Qual Saf. 2016; 25: 320-3.
  2. Girling AJ, Hofer TP, Wu J, et al. Case-mix adjusted hospital mortality is a poor proxy for preventable mortality: a modelling study. BMJ Qual Saf. 2012; 21(12): 1052-6.
  3. Hayward RA, Hofer TP. Estimating hospital deaths due to medical errors: preventability is in the eye of the reviewer. JAMA. 2001;286(4): 415-20.
  4. Benning A, Dixon-Woods M, Nwulu U, et al. Multiple component patient safety intervention in English hospitals: controlled evaluation of second phase. BMJ. 2011; 342:d199.

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