Aylin, P

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Making sense of the evidence for the “weekend effect”Sicker patients at the weekend, but even after adjustment for this their risk of death is higherPaul Aylin professor of epidemiology and public healthDr Foster Unit, School of Public Health, Imperial College London, London EC4Y 8EN, UKIn their analysis of 2013-14 English hospital administrativedata, Freemantle and colleagues again find an increased risk ofdeath in patients admitted at a weekend compared withweekdays.1Their analysis combines both emergency and electiveadmissions and updates their earlier study.2 They confirm apersistent “weekend effect” in England, which they claim is“not otherwise ignorable,” and add to a substantial body ofliterature demonstrating this phenomenon both nationally3-5 andinternationally.6-8The findings of such studies and the resultant media coverageare being used by politicians to bring about changes in workingpractices,9 but against a strong background of criticism of thesekinds of statistics.10 At first glance, there is conflicting evidenceabout whether the weekend effect exists at all.11 12 However,closer scrutiny shows that apparently “contradictory” studiestend to be smaller, carried out in single hospitals, and lackstatistical power. Death after hospital admission, particularlyfor a planned surgical procedure, is relatively rare, and smallstudies simply don’t have the numbers to be able to show aneffect.Freemantle and colleagues find an increased risk of death of10% for admissions on a Saturday and 15% for admissions ona Sunday compared with patients admitted on a Wednesday,which on the face of it, does not seem trivial. However, thisrepresents a 10-15% increase on a relatively low risk of deathoverall (1.8%). The difference between relative risk andattributable risk is key. Researchers in this area have oftenfocused on death as an outcome because it is important topatients and easily measured, but there is also evidence of aweekend increase in avertible errors in care leading to othercomplications.13 Though the proportion of admissions endingin death is relatively low, there is an assumption that anincreased risk of death may indicate a much greater burden ofcomplications and error, causing unnecessary harm to patients.An obvious criticism of some of these observational studies isthat patients admitted at the weekend are simply sicker.Freemantle and colleagues do indeed find a higher proportionof sicker patients at the weekend but attempt to account for thisby adjusting for case mix using a wide range of variablesincluded in administrative data. They are not the first group toadjust for this,3 yet the weekend effect seems to persist. Noattempt to account for sicker patients in an analysis is perfect,but risk adjustment models based on administrative data havebeen shown to be as good, if not better, than models based onclinical data.14 The possibility, however, of residual confoundingcan never be entirely ruled out.In an attempt to get around this problem, one of my group’sstudies looked at planned surgical procedures and focused onthe day of the week on which the procedure was performed.Wefound an increasing risk of death as the day of procedureapproached the weekend, with 44% higher odds of death if anoperation was carried out on a Friday (with the most criticalpostoperative period occurring over the weekend) comparedwith a Monday.4 The case mix of patients varies much less inplanned procedures on weekdays, and therefore confoundingwas less of a problem. In a follow-up paper, we also ruled outa lower level of experience in consultants carrying outprocedures on a Friday as a contributory factor for this effect.15Freemantle and colleagues look specifically at stroke as well asother conditions for which there is less reason to believe thatpatients would be sicker at the weekend.We have also examinedemergency stroke admissions and, even after adjusting for casemix, found not only an increased risk of death for patientsadmitted at the weekend but also that patients were less likelyto receive computed tomography on the day of admission, wereless likely to receive thrombolysis, had higher rates ofpneumonia, and were less likely to be discharged back to theirusual place of residence.16 This combination of both processand outcome measures strengthens the case for poorer qualityof care at the weekend. If patients were sicker, we might expecthigher rates of diagnostic tests and interventions.So if the “weekend effect” is real, what are the reasons behindpoorer outcomes? Freemantle and colleagues point towardsreduced services inside and outside the hospital as a possibleexplanation, but few studies have examined this important issuedirectly. Researchers in the US found a Friday effect innon-emergency major surgery but not in patients admitteddirectly to an intensive care unit, where there were moreconsistent levels of staffing throughout the week.17A recent UKstudy found that ward rounds by stroke specialists on sevendays a week did not affect risk of stroke mortality but did findan association with the intensity of weekend staffing byp.aylin@imperial.ac.ukFor personal use only: See rights and reprints http://www.bmj.com/permissions Subscribe: http://www.bmj.com/subscribeBMJ 2015;351:h4652 doi: 10.1136/bmj.h4652 (Published 5 September 2015) Page 1 of 2EditorialsEDITORIALSregistered nurses.18 A recent, very large European study founda strong relation between overall hospital mortality and nursestaffing and education.19Much evidence exists on the subject of weekend care, and thereis a need for a comprehensive systematic review of findings.More research is needed to understand the complex relationbetween staffing levels and services and patient safety, usingboth process and outcome measures. With promised changesto how the NHS provides weekend and out of hours care, it willbe an ideal opportunity to evaluate their impact on the “weekendeffect.”Competing interests: I have read and understood BMJ policy ondeclaration of interests and declare PA’s department has received aresearch grant and PA has received travel expenses from Dr FosterIntelligence.Provenance and peer review: Commissioned; not externally peerreviewed.1 Freemantle N, Ray D, Mcnulty D, et al. Increased mortality associated with weekendhospital admission: a case for expanded seven day services? BMJ 2015;351:h4596.2 Freemantle N, Richardson M, Wood J, et al. Weekend hospitalization and additional riskof death: An analysis of inpatient data. J R Soc Med 2012;105:74-84.3 Aylin P, Yunus A, Bottle A, Majeed A, Bell D.Weekendmortality for emergency admissions.A large, multicentre study. Qual Saf Health Care 2010;19:213-7.4 Aylin P, Alexandrescu R, Jen MH, Mayer EK, Bottle A. Day of week of procedure and 30day mortality for elective surgery: retrospective analysis of hospital episode statistics.BMJ 2013;346:f2424.5 Handel A, Patel S, Skinglsey A, Bramley K, Sobieski R, Ramagopalan SV. Weekendadmissions as an independent predictor of mortality: an analysis of Scottish hospitaladmissions. BMJ Open 2012;2:e001789.6 Bell CM, Redelmeier DA. Mortality among patients admitted to hospitals on weekends ascompared with weekdays. N Engl J Med 2001;345:663-8.7 Kostis WJ, Demissie K, Marcella SW, et al. Weekend versus weekday admission andmortality from myocardial infarction. N Engl J Med 2007;356:1099-109.8 Aylin P, Bottle RA, Ruiz M. The Global Comparators Project: international comparison of30-day in-hospital mortality by day of the week. BMJ Qual Saf 2015;24:492-504.9 Cameron D. A 7-day NHS, safe in our hands-for every generation to come. Speech, May2015. www.gov.uk/government/speeches/pm-on-plans-for-a-seven-day-nhs.10 McCartney M. The zombie statistic behind the push for seven day working. BMJ2015;351:h3575.11 Mikulich O, Callaly E, Bennett K, O’Riordan D, Silke B. The increased mortality associatedwith a weekend emergency admission is due to increased illness severity and alteredcase-mix. Acute Med 2011;10:182-7.12 Schmulewitz L, Proudfoot A, Bell D. The impact of weekends on outcome for emergencypatients. Clin Med 2005;5:621e5.13 Attenello FJ, Wen T, Cen SY, et al. Incidence of “never events” among weekendadmissions versus weekday admissions to US hospitals: national analysis. BMJ2015;350:h1460.14 Aylin P, Bottle A, Majeed A. Use of administrative data or clinical databases as predictorsof risk of death in hospital: comparison of models. BMJ 2007;334:1044.15 Ruiz M, Bottle A, Aylin PP. Exploring the impact of consultants’ experience on hospitalmortality by day of the week: a retrospective analysis of hospital episode statistics. BMJQual Saf 2015 Jul 22. [Epub ahead of print.]16 Palmer WL, Bottle A, Davie C, Vincent CA, Aylin P. Dying for the weekend: a retrospectivecohort study on the association between day of hospital presentation and the quality andsafety of stroke care. Arch Neurol 2012;69:1296-302.17 Zare MM, Itani KMF, Schifftner TL, HendersonWG, Khuri SF. Mortality after nonemergentmajor surgery performed on Friday versus Monday through Wednesday. Ann Surg2007;246:866-74.18 Bray BD, Ayis S, Campbell J, et al. Associations between stroke mortality and weekendworking by stroke specialist physicians and registered nurses: prospective multicentrecohort study. PLoS Med 2014;11:e1001705.19 Aiken LHD, SloaneM, Bruyneel L, et al. Nurse staffing and education and hospital mortalityin nine European countries: a retrospective observational study. Lancet 2014;383:1824-30.Cite this as: BMJ 2015;351:h4652© BMJ Publishing Group Ltd 2015For personal use only: See rights and reprints http://www.bmj.com/permissions Subscribe: http://www.bmj.com/subscribeBMJ 2015;351:h4652 doi: 10.1136/bmj.h4652 (Published 5 September 2015) Page 2 of 2EDITORIALS

Making sense of the evidence for the "weekend effect".

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Making sense of the evidence for the "weekend effect".

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