University of Birmingham researchers have found the concept of the so-called "weekend effect" on mortality rates for patients admitted to hospital on Saturdays and Sundays is a "major oversimplification" of a complex issue.
There has been much debate over the weekend effect, which suggests the mortality rate for patients admitted to hospital at weekends is higher than those admitted Monday to Friday.
But two new studies published in The Lancet suggest the concept may have been over simplified.
The first paper, led by the University of Birmingham, found no association between weekend senior doctor staffing levels and mortality.
Experts gathered data on senior doctor input into emergency admissions at 115 NHS trusts at two time points, Sunday 15 and Wednesday 18 June 2014.
They did find the mortality risk among patients admitted at weekends was higher than on weekdays.
But when they plotted mortality risk against senior doctor staffing levels, there was no evidence of an association between the two.
Lead author Professor Julian Bion, of the University of Birmingham, said:
The second paper, led by experts from King's College London and University College London, specifically looked at weekend stroke care.
They found no difference in 30-day survival for patients admitted during the day at the weekend, compared with during the week.
On Monday, Health Secretary Jeremy Hunt faced a grilling from MPs over the weekend effect - one of the key factors behind the Government's push for a seven-day NHS which has led to the dispute with junior doctors.
He told the Health Select Committee: