In a study by researchers in Liverpool, performed in men and women wanting proof of paternity from testing as well as studies based on genetic health screening, it was found that rates of cases where a man was not the biological father of his child was on average one in 25, ranging from 1% in some studies to as much as 30%.2 that the alleged father is not the biological father of the child.

copied from here

4% on average gives a better estimate than the often quoted maximum values. If one reads any number (advertisment or elsewhere) with the words "up to" preceeding the number, one should be very careful.

Wolfgang