LONDON, England -

A British study found that patients are more likely to die after surgery performed on a Friday.

Researchers from Imperial College London analyzed more than four million cases from around England over a three year period. They found that patients who underwent surgery on a Monday had the lowest risk of death. That risk rose as the week progressed.

For example, between Monday and Tuesday, there was a minimal change in the risk of death associated with surgery. But the risk rose by 15 percent on Wednesday, 21 percent by Thursday, and 44 percent by Friday.

Researchers analyzed elective surgeries only. They concluded that hospitals may have fewer qualified physicians scheduled toward the end of the week, as well as fewer diagnostic resources.

The study was published in The British Medical Journal.