British scientists say Thursday that as many as one in 25 fathers worldwide could be raising another man's child, believing he or she is his own.

Some of the mix-ups can be attributed to artificial insemination, but the majority are due to a woman having sexual relationships outside the marriage, says Professor Mark Bellis, one of the researchers.

Scientists at Liverpool's John Moores University examined the findings of dozens of studies, published over the past 54 years, on cases of paternal discrepancy -- where a man is proved not to be the biological father of his child, according to Reuters.

The studies come from countries as varied as the United States, Finland, New Zealand, South Africa and Mexico.

The findings of the studies vary dramatically -- some concluded that only one man in 100 is not the father of his child while others put the figure as high as 30 percent.

The Liverpool researchers calculate the median figure at around 4 percent, suggesting that as many as one in 25 men worldwide is not the biological father of a child he believes to be his.