In his The "Sissy Boy Syndrome" and the Development of Homosexuality (1987), the sexologist Richard Green compared two groups of boys: one group was conventionally masculine; the other group, who Green called "feminine boys" and other children called "sissy", engaged in doll play and other behavior typical for girls.[16] In his 15-year longitudinal study, Green looked at cross-gender behavior in boys who later turned out to be transgender, or homosexual as well as a control group, and analyzed such features as interest in sports, playroom toy preferences, doll-play fantasy, physical behavior ("acting like a girl" vs rough-and-tumble play), cross-dressing, and psychological behavior,[16]:21–29 using tests, questionnaires, interviews, and follow-ups. He also looked at the influence of parental relationships [16]:353–369and reaction to atypical behavior. Later follow-ups found that 3/4 of his feminine or "sissy" boys became gay or bisexual men, whereas only one of the control group did.