What have we learnt after 15 years of research into the 'weekend effect'?

It is now 15 years since Bell and Redelmeier published their landmark study demonstrating higher mortality for people admitted to hospital during weekends compared with during the week. Examining the records of 3.8 million patients admitted over a 10-year period to emergency departments in Ontario, Canada, this ‘weekend effect’ existed over a range of acute conditions, including 23 out of the 100 leading causes of death. Since that paper in 2001, over 100 studies have explored the weekend effect, across a range of patient populations and health systems. Surprisingly, despite this large number of studies, there remains ongoing debate about whether the weekend effect exists, and if so, what causes it. For example, one recent and highly influential study found higher rates of in-hospital death following admission on Saturday or Sunday compared with Wednesday admissions (HR 1.10 for Saturday and 1.15 for Sunday). Policy makers and politicians in England have frequently referred to this result and those of other research studies on the weekend effect in justifying existing moves to provide more consistent 7-day health services. The nature of some of the proposed measures, including changes in doctors’ work contracts, have proven extremely controversial, contributing to the first large-scale strike by doctors in England in over 40 years. Controversies over the weekend effect have not been limited to the political arena. Some researchers have questioned the existence of the weekend effect, while others have highlighted the uncertainty about what causes it. Given these persistent controversies and questions, including those generated by the paper by Anselmi et al in this issue, it seems fitting to ask what have we really learnt about the quality and safety of healthcare from 15 years of studies into the weekend effect.