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## Statistics in the News: Chapter 7 Presenting Data: Summary Measures

Bad Idea: Getting Sick on the Weekend

The level of staffing in hospitals is often lower on weekends than on weekdays, despite a presumably consistent day-to-day burden of disease. Therefore, we may well ask: Do in-hospital mortality rates among patients with serious conditions differ according to whether patients are admitted on a weekend or on a weekday?

The results of a recent study provide an answer. Two researchers analyzed all acute care admissions from emergency departments in Ontario, Canada, between 1988 and 1997 (a total of 3,789,917 admissions). After comparing in-hospital mortality among patients admitted on a weekend with that among patients admitted on a weekday, they concluded that weekend admissions were associated with significantly higher mortality rates for 23 of the 100 leading causes of death and were not associated with significantly lower mortality rates for any of these causes of death.

The researchers also noted that patients with some serious medical conditions (other than the leading causes of death) are more likely to die in the hospital if they are admitted on a weekend than if they are admitted on a weekday. Table A summarizes the results for three of these conditions (after adjustment for age, sex, and coexisting disorders). An examination of relevant proportions leads to the conclusion that patients with some serious medical conditions are more likely to die in the hospital if they are admitted on a weekend than if they are admitted on a weekday.

Table A In-Hospital Mortality Rates According to Day of Admission
 Condition Number of Admissions Mortality Rate (proportion) p Value for Difference Odds Ratio and 95% Confidence Interval Weekend Admission Weekday Admission Ruptured abdominal aortic aneurysms 5,454 .42 .36 <.001 1.28(1.13 - 1.46) Acute epiglottitis 1,139 .017 .003 .04 5.28(1.01 - 27.50) Pulmonary embolism 11,686 .13 .11 .009 1.19(1.03 - 1.36)

The researchers suggested a number of explanations, such as

• fewer people work in hospitals on weekends than on weekdays,
• those who do work on weekends often have less seniority and experience than those who work on weekdays,
• weekend staff often provide coverage for other health professionals and may be less familiar with the patients under their charge, and
• there are also fewer supervisors on weekends, and they are often responsible for overseeing the work of staff members they do not know well.

Note: The Table A data are scary. However, for 77 of the 100 leading causes of death admission on a weekend was not associated with a significantly higher rate of death than was admission on a weekday. These 77 causes accounted for 84 percent of all admissions and for 72 percent of all deaths. Thus, the scary weekend-death association was not found for acute myocardial infarction or for most of the other conditions that commonly call for inpatient medical therapy, such as heart failure, pneumonia, stroke, asthma, and gastrointestinal bleeding. Nor was it found for conditions that frequently require admission from the emergency department for surgery, such as hip fracture, cholelithiasis, and intestinal obstruction.

Sources. Adapted from Chaim M. Bell and Donald A. Redelmeier, "Mortality Among Patients Admitted to Hospitals on Weekends as Compared With Weekdays," The New England Journal of Medicine, August 30, 2001, pp. 663-668, and Ethan A. Halm and Mark R. Chassin, "Why Do Hospital Death Rates Vary?" The New England Journal of Medicine, August 30, 2001, pp. 692-694.