Patients are not a greater risk of dying on weekends than at any other times, a British academic has argued.
Professor Dr Nick Black warned politicians needed 'to avoid unjustified claims about an increased risk of death among patients' because of the so-called weekend effect.
This was the justification used by Jeremy Hunt to implement a seven-day-a-week NHS and impose new contracts on junior doctors leading to the first ever strike when they refused to provide emergency cover.
The Professor of Health Services Research at the London School of Hygiene and Tropical Medicine said past studies had incorrectly estimated mortality at up to a sixth higher for weekend admissions.
He said: "Concern about patients having a higher risk of dying if admitted to a hospital on Saturday or Sunday, the so called weekend effect, has taken on great political importance in England over the past year.
"This issue has advanced from being a long-standing topic of interest only to health services researchers and policy makers to one that has assumed high media coverage when the Secretary of State for Health, Jeremy Hunt, cited it as the prime reason for increasing service provision on weekends and, in turn, why the junior doctors in the NHS should accept new terms and conditions of service.
"In support of Hunt's claims, the Department of Health for England assembled an overview of the topic and concluded that there was 'significant evidence demonstrating this weekend effect'.
But he said researchers have re-examined the evidence of the weekend effect that dates back to the 1970s.
He added around 2010 'some ambitious attempts were made in England to compare the mortality for the entire patient population admitted during weekends versus weekdays, rather than focusing on specific diseases, as previous studies had'.
"These studies reported mortality at 10 per cent to 15 per cent higher for weekend admissions. However, these analyses were based on administrative databases that have little information about the clinical state of patients at the time of admission."
In an opinion piece published in the journal JAMA, he argued this 'contributed to misleading findings'.
Inconsistent diagnostic coding, insufficient consideration of comorbidity and failure to consider the severity or acuity of patients' illnesses were subsequently addressed by new studies.
And stronger evidence has since emerged by using a recently introduced standard measure of risk of dying based on seven physiological variables - the National Early Warning Score or NEWS.
He said: "In a study conducted at three general hospitals, the authors found that patients admitted on weekends had greater severity of illness than those admitted on weekdays and had a 10 per cent higher risk of dying, but when NEWS was considered in the analysis, the difference in mortality between weekend and weekday admissions no longer existed.
"These recent studies suggest that patients admitted during weekends are at no greater risk of dying than those admitted during the week.
"The results of the various recent studies do not mean there is no weekend effect, only that if care provided during weekends is poorer than on weekdays, it does not result in patient deaths.
"This should come as no surprise given evidence that death is not a particularly sensitive measure of the overall quality of hospital care because only about four per cent of hospital deaths are thought to be avoidable."
To determine if the concerns were justified researchers should look at other dimensions of quality such as health outcomes, patient safety, patients' experience and educational quality of doctors on call.
He concluded: "In the meantime, policymakers need to avoid unjustified claims about an increased risk of death among patients admitted during weekends because doing so only serves to undermine public confidence and trust in hospitals and damage staff morale.
"Neither of these are in the interest of patients or the public."