Yet Again, Low Proportion of Hospital Deaths Judged Preventable

Hogan and colleagues have reported another study on preventable mortality based on case-note review among 34 hospitals.[1] Only 3.6% of deaths were thought to have been preventable on the balance of probability. Preventability rates did not vary widely between hospitals.

Of course, this might be something of an underestimate because deaths where the probability of preventability was less than 50% are not included. The CLAHRC WM Director calculates preventability as the sum of all cases that may have been preventable, weighted by the probability that they were preventable. He also likes to adjust for the reviewer effect to minimise the influence of unusually ‘hawkish’ reviewers.

Despite these precautions, preventability is “in the eye of the reviewer,”[2] and may be over-estimated because of hindsight bias, or under-estimated because some practices that may increase the risk of death cannot be discerned from case-notes.

— Richard Lilford, CLAHRC WM Director


  1. Hogan H, Zipfel R, Neuburger J, Hutchings A, Darzi A, Black N. Avoidability of hospital deaths and association with hospital-wide mortality ratios: retrospective case record review and regression analysis. BMJ. 2015; 351: h3239.
  2. 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.

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