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The Freemantle1 paper published in the BMJ in 2015 which claimed to be the most robust analysis of the weekend effect to date made the following bold claim:
“An advantage of the statistical method that we used is that it is not subject to bias caused by systematic differences in coding practices between hospitals. Furthermore, any differences in coding practice between the weekend and weekdays within all hospitals are captured in our estimate of additional severity of weekend admissions and thus do not affect interpretation of the results.”
The paper by Li seems to show that biases in coding practices between the weekend and the weekdays cannot be overcome by purely statistical means.
1 Freemantle N, Ray D, McNulty D, Rosser D, Bennett S, Keogh B E Pagano D. Increased mortality associated with weekend hospital admissions: a case for expanded seven day serves? BMJ 2015;351:h4596 http://www.bmj.com/content/351/bmj.h4596
No competing interests
19 May 2016
Anthony P Roberts
Deputy Director (Clinical Effectiveness)
South Tees Hospitals NHS Foundation Trust
The James Cook University Hospital, Marton Road, Middlesbrough, TS4 3BW