...there are at least three levels of sampling involved in work like Kinsey's. As already noted, the samples of the population (first level) are far from random and so may not be particularly representative of any population. It is equally important to remember that any questionnaire is only a sample (another level) of the possible questions; and that the answer the gentleman or lady gives is no more than a sample (third level) of his or her attitudes and experiences on each question.