Published 29 April 2009, doi:10.1136/bmj.b1745
Cite this as: BMJ 2009;338:b1745

Letters

Standardised mortality ratios

Monitoring mortality

The first 150 words of the full text of this article appear below.

Mohammed and colleagues suggest that hospital standardised mortality ratios are prone to the "constant risk fallacy" and that the use of certain variables (the Charlson comorbidity index and emergency admission) for the case mix adjustment model is "unsafe."^{1 2}

They focus on at least two mechanisms that might contribute to this constant risk fallacy: differential measurement error, and inconsistent proxy measures of risk. Certainly, measurement error, including poor coding, will have an impact on the ratios. However, it is the extent to which they are affected which is important. The paper gives a hypothetical example of how differential measurement error can distort a standardised mortality ratio. This is an extreme example based on artificial data.

We calculated 2007-8 hospital standardised mortality ratios with and without adjustment for comorbidity (using the Charlson index) for each of the four hospitals in the paper and found that they changed by less than 3%. The . . . [Full text of this article]

¹ Dr Foster Unit at Imperial, Department of Primary Care and Social Medicine, Imperial College London, Jarvis House, London EC1A 9LA

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Authors’ reply

Mohammed A Mohammed, Jonathan J Deeks, Alan Girling, Gavin Rudge, Martin Carmalt, Andrew J Stevens, and Richard J Lilford
BMJ 2009 338: b1750. [Extract] [Full Text]

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This article has been cited by other articles:

• Mohammed, M. A, Deeks, J. J, Girling, A., Rudge, G., Carmalt, M., Stevens, A. J, Lilford, R. J (2009). Authors' reply. BMJ 338: b1750-b1750 [Full text]  

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