The old adage is “Statistics can lie.” In England, there is a full-blown statistical battle revolving around the alleged increased mortality rate among patients admitted to hospitals on weekends. One study found that more people die in hospitals on weekends, while another study contradicts the evidence, finding that fewer people die in hospitals on weekends.

Those espousing the theory that the death rate is higher on weekends say it’s because more young physicians work on weekends and there are fewer staff members on duty.

But a University of Manchester team found an apparently simple answer to the question of why the death rate rises on the weekend among patients admitted via emergency room. The study found that there is indeed a “weekend effect,” because fewer people are admitted and they are the sickest patients, leading to a higher death rate than during the week.

“Hospitals apply a higher severity threshold when choosing which patients to admit to the hospital at weekends – patients with non-serious illnesses are not admitted, so those who are admitted at the weekend are on average sicker than during the week and more likely to die regardless of the quality of care they receive,” said Matt Sutton, who headed up a research team. “As a result, the figures comparing death rates at weekends and weekdays are skewed. The NHS has rushed to fix a perceived problem that further research shows does not exist.”

The same is true for patients admitted to the actual hospital, not just the ER. A study published in the British Medical Journal last September looked at patients admitted to a hospital and found that the patients admitted during the weekend were sicker than patients admitted during the week, but suggested that having more staff working could reduce the mortality rate.

Though the study did not look into the reasons why the risk of death was higher on the weekend, the study’s authors hypothesized several explanations, including: understaffed hospitals with less-experienced workers; longer wait periods for patients; and reduced access to test results and diagnostics on the weekend.

The team from the University of Manchester’s Centre for Health Economics dispute that. They looked at all patients attending A&E departments (emergency departments) between April 2013 and February 2014. They say the earlier study did not take into account the drop in the numbers. At the weekend, they have found, hospitals admitted 7% fewer patients.

According to a study reported in The Lancet, increased mortality rates associated with weekend hospital admissions – the so-called “weekend effect” – have been attributed to suboptimum staffing levels of specialist consultants. The study set out to examine preliminary associations between specialist intensity and weekend admission mortality across the English National Health Service. In plain English, was the theory of an increased likelihood of death on a weekend admission true?

Eligible British hospitals were those in England receiving unselected emergency admissions. On a June weekend in 2014, the study group surveyed hospital specialists to obtain data related to the care of patients admitted as emergencies. The study defined specialist intensity at each hospital as the self-reported estimated number of specialist hours per 10 emergency admissions. With use of data for all adult emergency admissions for financial year 2013–14, the study compared weekend to weekday admission risk of mortality with the Sunday to Wednesday specialist intensity ratio within each hospital. The study also stratified hospitals by number of beds.

This study was not a small sample size as 127 of 141 eligible acute hospitals agreed to participate. Of the 127 participating, 115 hospitals (91 percent) contributed data to the point-prevalence survey. Of the 34,350 clinicians surveyed, 15,537 (45 percent) responded. Not surprisingly, substantially fewer specialists were providing care to emergency admissions on a Sunday (1667, or 11 percent) than on a Wednesday (6,105, or 42 percent).

Specialists working at the hospital on Sunday spent 40 percent more time caring for emergency patients than did those present on Wednesday. This cross-sectional analysis did not detect a correlation between weekend staffing of hospital specialists and mortality risk for emergency admissions.

So what does all this statistical data mean? No one is quite sure yet. However, if given the choice, you might prefer to wait until Monday for any ER or scheduled surgery.