E. Sandra Byers and Raymond J. Eno, "Predicting Men's Sexual Coercion and Aggression from Attitudes, Dating History, and Sexual Response", Journal of Psychology and Human Sexuality, Vol. 4(3) (1991). See pages 61, 68.

For more info on the questionnaire used in this study to measure attitudes towards porn and sex, see:

William Fisher, Donn Byrne, Leonard White, and Kathryn Kelley, "Erotophobia-Erotophilia as a Dimension of Personality", Journal of Sex Research Vol. 25, No. 1 (February 1988).