Nor is it only the Idols: previous studies have found similar biases in the Eurovision song contest and other sequential judged competitions.
Katie and Lionel Page based their findings on a statistical analysis of 1522 performances over 165 Idol shows in the United States, Australia, Brazil, Canada, Germany, India and the Netherlands between 2003 and 2007, and Britain's X-Factor.
They found that even after accounting for a contestant's talent, those who performed later in the Idol show had an advantage over other contestants.
Contestants who performed last were significantly more likely to avoid the elimination round than could be expected by chance alone.
"We found that the order contestants performed mattered," Dr Katie Page said. "It's much better to go last.
"The later a contestant performs in a show, the more likely they are to not be in the bottom two in the following round."
The researchers also found that contestants who performed first were more likely to be judged favourably than those who went second or third - which were found to be the worst slots on the programme.
And following a bad act also hammered a contestant's chances.
"Our results indicate that judges tend to assess performances based on similarities with the previous contestant and not differences," said Dr Lionel Page, a postdoctoral fellow of the university's Business School.
"If you perform after a weak contestant there is a bias.
"You are more likely to be evaluated poorly than if you perform after a strong contestant."
Dr Lionel Page said that the effect was especially strong in the earlier rounds because no favourites had emerged.
"As the show progresses, the favourite contestants are likely to be safe regardless of the order they perform in," he said.
"But for lower candidates, performing last can make a big difference."
- staff reporter
