Do studies of the weekend effect really allow for differences in illness severity?

For nearly 15 years from 1997 until 2011, David Barer and his stroke team colleagues kept a prospective register of all patients admitted to hospital in Gateshead with suspected acute stroke. This was used mainly for research but also allowed independent checks to be made on the official figures from the coding department, providing useful insights into diagnostic uncertainties, the reasons for coding errors and day-to-day and year-on-year changes in the numbers and clinical characteristics of stroke admissions.  In this study he analyses whether the apparent excess mortality among patients admitted at weekends might be due to differences in stroke severity or other factors which cannot be measured in studies relying on routine administrative data.

strokeThe long-rumoured but now notorious “weekend effect” recently received the seal of scientific respectability from two huge studies, analysing routine data on 20 million hospital admissions (and 1/2 million deaths) in England and Wales. They found a 10-15% increase in the risk of dying in the first month after weekend, compared with weekday admissions, even after adjusting for differences in overall “sickness levels” by sophisticated modelling of diagnostic and administrative data.  The authors of the larger study even included non-emergency admissions, despite the obvious imbalance between weekdays and weekends, arguing that their risk model could “explain” most of the mortality variation.  Continue reading