The Global Comparators project: international comparison of 30-day in-hospital mortality by day of the week.

OBJECTIVE: To examine the association of mortality by day of the week for emergency and elective patients.

DESIGN: Retrospective observational study using the international dataset from the Global Comparators (GC) project consisting of hospital administrative data.

SETTING: 28 hospitals from England, Australia, USA and the Netherlands during 2009-2012.

PARTICIPANTS: Emergency and surgical-elective patients.

MAIN OUTCOME MEASURES: In-hospital deaths within 30 days of emergency admission or of elective surgery.

RESULTS: We examined 2 982 570 hospital records; adjusted odds of 30-day death were higher for weekend emergency admissions to 11 hospitals in England (OR 1.08, 95% CI 1.04 to 1.13 on Sunday), 5 hospitals in USA (OR 1.13, 95% CI 1.04 to 1.24 on Sunday) and 6 hospitals in the Netherlands (OR 1.20, 95% CI 1.09 to 1.33 on Saturday). Emergency admissions to the six Australian hospitals showed no daily variation in adjusted 30-day mortality, but showed a weekend effect at 7 days post emergency admission (OR 1.12, 95% CI 1.04 to 1.22 on Saturday). All weekend elective patients showed higher adjusted odds of 30-day postoperative death; we observed a 'Friday effect' for elective patients in the six Dutch hospitals.

CONCLUSIONS: We show that mortality outcomes for our sample vary within each country and per day of the week in agreement with previous studies of the 'weekend effect'. Due to limitations of administrative datasets, we cannot determine the reasons for these findings; however, the international nature of our database suggests that this is a systematic phenomenon affecting healthcare providers across borders. Further investigation is needed to understand the factors that give rise to the weekend effect. The participating hospitals represent varied models of service delivery, and there is a potential to learn from best practice in different healthcare systems.