In genetics, a non-paternity event (also known as misattributed paternity, not parent expected, or NPE) is when someone who is presumed to be an individual's father is not in fact the biological father. This presumption may be on the part of the individual, the parents, or the physician. Non-paternity may result from sperm donation, undisclosed adoption, heteropaternal superfecundation, promiscuity, paternity fraud, or sexual assault, as well as medical mistakes, for example, mixups during procedures such as in vitro fertilization and artificial insemination. Where there is uncertainty, the most reliable technique for establishing paternity is genetic testing; however, there is still a risk of error due to the potential for gene mutations or scoring errors.