Data linkage studies can help to explain the weekend effect
Authors: Benjamin D Bray, Adam Steventon
Journal: The Lancet (2017)

Is the weekend effect a worrying manifestation of systematic deficiencies in the quality and safety of health care, or instead simply an artefact, constructed from confounding, bias, and the imperfections of existing methods for making sense of observational data? This question has not only motivated a huge number of research studies,1Li L Rothwell PM Oxford Vascular StudyBiases in detection of apparent 'weekend effect' on outcome with administrative coding data: population based study of stroke.BMJ. 2016; 353: i2648Crossref PubMed Scopus (59) Google Scholar but also entered the arena of politics and policy, contributing in England to the first industrial protest by junior doctors in 40 years.2Goddard AF Lessons to be learned from the UK junior doctors' strike.JAMA. 2016; 316: 1445Crossref PubMed Scopus (15) Google Scholar Although the consequences are hard to measure, popular awareness of the weekend effect could plausibly have fostered anxiety in the minds of patients and families about the safety of seeking health care at the weekend. Although most studies agree that mortality rates are higher for patients admitted to hospital at the weekend than during the week, the extent to which this effect reflects the care provided versus the characteristics of the patients admitted has been unclear. Studies have largely used administrative data gleaned from discharge coding, which contain limited information on illness severity.3Black N Higher mortality in weekend admissions to the hospital: true, false, or uncertain?.JAMA. 2016; 316: 2593-2594Crossref PubMed Scopus (23) Google Scholar The study4Walker AS Mason A Quan TP et al.Mortality risks associated with emergency admissions during weekends and public holidays: an analysis of electronic health records.Lancet. 2017; (published online May 9.)http://dx.doi.org/10.1016/S0140-6736(17)30782-1Google Scholar by A Sarah Walker and colleagues in The Lancet provides new insights by drawing on a large database of linked administrative and laboratory data.4Walker AS Mason A Quan TP et al.Mortality risks associated with emergency admissions during weekends and public holidays: an analysis of electronic health records.Lancet. 2017; (published online May 9.)http://dx.doi.org/10.1016/S0140-6736(17)30782-1Google Scholar When the researchers limited their analysis to variables from administrative data (such as diagnosis codes), relative mortality risk was similar to that previously found: 8–9% higher at the weekend. However, the results of common biochemical and haematological tests explained 33% (95% CI 21–70) of the excess mortality on Saturdays and 52% (lower 95% CI 34) on Sundays, significantly reducing the size of the weekend effect when those variables were included. Striking differences were found in the blood test results between weekends and weekdays, with proportionately fewer patients with normal results being admitted at the weekend. This result suggests that part of the explanation for the weekend effect is proportionally fewer admissions for minor illness at the weekend, resulting in a cohort of patients with higher average risk of mortality compared with the weekday cohort. That said, even after adjusting for laboratory data, risk of mortality remained 18% higher for patients admitted between 1100 h and 1500 h on weekends. Further investigation is warranted, especially because another study5Anselmi L Meacock R Kristensen SR et al.Arrival by ambulance explains variation in mortality by time of admission: retrospective study of admissions to hospital following emergency department attendance in England.BMJ Qual Saf. 2016; (published online Oct 18.)https://doi.org/10.1136/bmjqs-2016-005680Crossref PubMed Scopus (41) Google Scholar has recently found similar levels of raised mortality on weekday afternoons. The authors modelled the relationship between mortality and hospital workload (eg, admission rates and bed occupancy). Their reasoning was that if the weekend effect is linked to reduced staffing levels or access to services, then the weekend effect should be diminished when controlling for busy days—eg, when the hospital is fuller than average. In fact, controlling for workload did not affect excess mortality following weekend admission. Although this result is intriguing, workload data are difficult to substitute for direct data on staffing levels and, in our view, stronger evidence is available from elsewhere regarding weekend mortality and staffing levels.6Aldridge C Bion J Boyal A et al.Weekend specialist intensity and admission mortality in acute hospital trusts in England: a cross-sectional study.Lancet. 2016; 388: 178-186Summary Full Text Full Text PDF PubMed Scopus (81) Google Scholar, 7Bray BD Ayis S Campbell J et al.Associations between stroke mortality and weekend working by stroke specialist physicians and registered nurses: prospective multicentre cohort study.PLoS Med. 2014; 11: e1001705Crossref PubMed Scopus (81) Google Scholar Walker and colleagues' contribution might be better located within the growing literature on hospital workload.8Snowden JM Kozhimannil KB Muoto I Caughey AB McConnell KJ A 'busy day' effect on perinatal complications of delivery on weekends: a retrospective cohort study.BMJ Qual Saf. 2017; 26: e1Crossref PubMed Scopus (29) Google Scholar At a time when occupancy rates are running at around 95% for general and acute beds in the English National Health Service, more studies should follow their approach and consider the implications of busy hospitals for quality and safety. Based on this study4Walker AS Mason A Quan TP et al.Mortality risks associated with emergency admissions during weekends and public holidays: an analysis of electronic health records.Lancet. 2017; (published online May 9.)http://dx.doi.org/10.1016/S0140-6736(17)30782-1Google Scholar and other evidence,3Black N Higher mortality in weekend admissions to the hospital: true, false, or uncertain?.JAMA. 2016; 316: 2593-2594Crossref PubMed Scopus (23) Google Scholar it now seems likely that many of the highest profile studies of the weekend effect overstated the problem by relying too heavily on administrative data. With this consideration in mind, it is striking that the oldest laboratory data used in this latest study were collected over a decade ago, accumulating steadily within the electronic depths of clinical databases. In other words, the data used by Walker and colleagues predate some of the most controversial studies into the weekend effect,9Freemantle N Richardson M Wood J et al.Weekend hospitalization and additional risk of death: an analysis of inpatient data.J R Soc Med. 2012; 105: 74-84Crossref PubMed Scopus (212) Google Scholar and might have informed policy and practice years ago. Considering the potential implications of the weekend effect, for public confidence as well as safety, this observation is challenging for all those involved in using real world data for research and service improvement. Substantial investments have been made in big data initiatives, mainly focused on development of new clinical interventions10Schneeweiss S Learning from big health care data.N Engl J Med. 2014; 370: 2161-2163Crossref PubMed Scopus (214) Google Scholar (sometimes breathlessly described in the heroic language of the so-called moonshot11National Cancer InstituteCancer Moonshot.https://www.cancer.gov/research/key-initiatives/moonshot-cancer-initiativeGoogle Scholar) but the same data and techniques could more modestly be used to understand and improve care for the patients of today. The story of the weekend effect should motivate health-care services and researchers to use and share data more effectively, apply more sophisticated approaches to assessing care quality, and build the evidence base so badly needed for health-care improvement. We declare no competing interests. Mortality risks associated with emergency admissions during weekends and public holidays: an analysis of electronic health recordsAdjustment for routine test results substantially reduced excess mortality associated with emergency admission at weekends and public holidays. Adjustment for patient-level factors not available in our study might further reduce the residual excess mortality, particularly as this clustered around midday at weekends. Hospital workload was not associated with mortality. Together, these findings suggest that the weekend effect arises from patient-level differences at admission rather than reduced hospital staffing or services. Full-Text PDF Open Access