The Friendship Questionnaire: an investigation of adults with Asperger syndrome or high-functioning autism, and normal sex differences.

Friendship is an important part of normal social functioning, yet there are precious few instruments for measuring individual differences in this domain. In this article, we report a new self-report questionnaire, the Friendship Questionnaire (FQ), for use with adults of normal intelligence. A high score on the FQ is achieved by the respondent reporting that they enjoy close, empathic, supportive, caring friendships that are important to them; that they like and are interested in people; and that they enjoy interacting with others for its own sake. The FQ has a maximum score of 135 and a minimum of zero. In Study 1, we carried out a study of n = 76 (27 males and 49 females) adults from a general population, to test for previously reported sex differences in friendships. This confirmed that women scored significantly higher than men. In Study 2, we employed the FQ with n = 68 adults (51 males, 17 females) with Asperger Syndrome or high-functioning autism to test the theory that autism is an extreme form of the male brain. The adults with Asperger Syndrome or high-functioning autism scored significantly lower on the FQ than both the male and female controls from Study 1. The FQ thus reveals both a sex difference in the style of friendship in the general population, and provides support for the extreme male brain theory of autism.