Simplify the following text for a Grade 9 native English-speaking person.
Original: Prevalence is difficult to generalize , but research has estimated 10 â `` 15 % of the general population as having at least one such sexual contact , with less than 2 % involving intercourse or attempted intercourse .
Simplified: It is difficult to say how frequent incest is , but researchers have estimated that between 10 % and 15 % of people have at least one incest experience . Less than 2 % of these involve intercourse or attempted intercourse .