Method ------ **Participants and Procedure** Data from this study will be drawn from the Zagreb and Rijeka panel samples recruited in the PROBIOPS project (for details see, https://osf.io/4q68c/). This project included N = 2,235 2nd year high-school students from 59 of 70 schools in the city of Zagreb, the capital of Croatia, and the surrounding area to participate in a 6-wave longitudinal study concerning sexual media use. A further sample of N = 1,744 2nd year high-school students were recruited from 14 of 22 schools in the city of Rijeka, the third largest city in Croatia. While the participants in the Zagreb panel completed all measures online, the Rijeka panel used pen and paper assessments conducted in classrooms during school hours under the supervision of a research assistant. In this case, privacy screens were placed between students to maintain confidentiality. The first assessments were conducted in 2015 and follow-up waves occurred in approximately 6 month intervals. In the analyses presented in this study, we used a subsample of male adolescents who participated in the relevant waves (when topic-specific measures were assessed). In the Zagreb panel, waves T1, T2, T4, and T5 will be used while in the Rijeka panel, data will be used from waves T2-T6 (except for time invariant data concerning self-assessed pubertal status, which was assessed only at T1). Both panels were further screened for participants who reported a (nonsensical) decrease in the number of lifetime sexual partners. All questionnaires contained contact information for youth psychological health services. Some compensation for participation was offered to the Zagreb panel members but not to participants in the Rijeka panel. Following national guidelines for ethical research with minors, students were asked to provide informed consent at each wave. Prior to the study launch, their parents were sent information about the longitudinal study and its aims. All procedures were reviewed and approved by the Ethical Research Committee of the University of Zagreb. Measures **Sexual Aggression.** Sexual aggression was measured at waves T1-T5 in the Zagreb sample and waves T1-T6 in the Rijeka sample. It was initially assessed with a single-item general indicator that was previously used in research involving adolescents (Ybarra et al., 2011): “How many times have you kissed, touched, or done anything sexual with another person when that person did not want you to do so?” After the baseline assessment, the phrase “How many times” was replaced with “In the last 6 months.” Responses were measured with a three-point scale: “Never,” “once,” and “several times.” Responses were dichotomized by collapsing together “once” and “several times.” **Hostile Masculinity.** Hostile masculinity was measured at waves T1-T5 (except for T3) in the Zagreb panel and T2-T6 in the Rijeka panel with a 5-item adapted version of Lonsway and Fitzgerald’s (1995) Hostility Towards Women scale. The Lonsway and Fitzgerald (1995) scale is itself a modified version of Check et al.’s (1985) Hostility Towards Women scale which has been used as one of two highly correlated components of Hostile Masculinity in previous Confluence Model research (Malamuth et al., 2000). Examples of items used in the current study included “I feel that many times women flirt with men just to tease them or hurt them” and “Women are responsible for most of my troubles.” Responses were collected on a 5-point scale that ranged from “strongly disagree” to “strongly agree.” Responses will be summed into a composite indicator of Hostile Masculinity. **Impersonal Sexuality.** Total number of sexual intercourse partners will be used as an index of impersonal sexuality. Again, this is one of two components that has been used in past Confluence Model research (Baer et al., 2015, Malamuth et al., 2000). At each wave participants were asked if they had sexual intercourse. If confirmed that they had, they were further asked: “In total, with how many different people did you have a sexual intercourse since your first time?” Participants who did not report a sexual intercourse were assumed to have had no sexual partners. Further, in cases when participants lacked data for a specific wave but their reported number of sexual partners was stable across the preceding and following assessments, the missing data was replaced with the number of sexual partners that they reported before and after the gap. **Pornography Use.** Pornography use was assessed at each wave in both panels. After defining pornography as “any material which openly depicts sexual activity; material which shows naked bodies but not sexual intercourse or other sexual activity does not belong to pornography as here defined,” participants were asked about their use of pornography in the past 6 months. Response options were: 1 – “not once”; 2 – “several times a month”; 3 – “once a month”, 4 – “2-3 times a month”; 5 – “once a week”, 6 – “several times a week”, 7 – “every day or almost every day”; and 8 – “several times a day.” **Coercive and Violent Pornography Use.** At each wave, participants in the Zagreb panel were asked two questions related to the use of violent and coercive pornography. Specifically, participants were asked if the pornography they usually use involved “A person who looks as if she/he is forced to do something” and “A person suffering and in pain.” A binary yes/no format was used to anchor answers. Responses to the two items were combined to indicate either no preference for violent and/or coercive pornography (coded 0) or a preference for this type of content (coded 1). **Masturbation.** The frequency of masturbation was used as a proxy measure of solitary sexual desire and was assessed twice in the Zagreb panel (T1 and T4) and once in Rijeka (T6) with the following question: “How often have you masturbated in the past six months?” In Zagreb, the T1 and T4 average was used as the estimated masturbation frequency. **Testosterone.** Salivary samples were collected at T6 in the Rijeka sample to measure testosterone levels. Testing procedure and equipment were pre-tested in May 2017 in a group of 40 18-year-old high-school students from a small urban setting. Recruitment leaflets for the main study were distributed in schools during the final data collection wave at the beginning of March 2018. Biological data collection was organized in a local youth club, Monday to Friday from noon to 2 PM, in the March 5-30 period. After informed consent was obtained, participants were asked to fill out a brief questionnaire about their behaviors in the past 24 hours and chronic conditions that could influence testosterone (T) level (e.g., sexual activity, hours of sleep, bleeding gums, etc.). Only participants of legal age who participated in at least two study waves (of the total of six) were eligible for the biological component. Biological data was linked to survey data using the same 5-digit alphanumerical code which participants would generate at each study wave. Participation was awarded with a 6.5€ ($7.5) shopping mall voucher. In total, 252 saliva samples were collected—more than 80% of them between 1 and 3 PM—by passive drool using Salimetrics’ Saliva Collection Aid and cryovials and stored at –70°C until required for analysis. After thawing, each sample was centrifuged for ten minutes at 2245 g at least once to separate the mucins. Clear colorless supernatants were then tested. Salivary T levels were measured in triplicate using a commercial enzyme-linked immunosorbent assay (Testosterone free in saliva ELISA test kit #DES6622, Demeditec, Germany) according to manufacturer’s instructions. The average intra-assay and inter-assay coefficients of variation for the T assay employed in the current study were 6,76% and 5,6% respectively. The range of the assay, as determined by manufacturer, was 10–1000 pg/ml. The lowest analytically detectable T level (i.e., distinguishable from the Zero Calibrator) was 2.2 pg/ml at -/+ 2 SD limit. Certificates of quality control were provided for all ELISA kits. **Pubertal Status.** The construct was measured at baseline, in both panels, using a single relative-rating item that has been used in previous research (Petersen et al., 1988). The self-reported onset of puberty (“In comparison to others, your physical development began…”) was assessed by a 5-point scale ranging from 1 – “much earlier than in your peers” to 5 – “much later than in your peers.” **Impulsiveness.** Impulsiveness was measured with an adapted 8-item version of the Barratt Impulsiveness Scale-Brief (Steinberg et al, 2013) at T4 in the Zagreb panel and T2, T3 and T6 in the Rijeka panel. Example items included “I do things without thinking” and “I am future oriented.” Responses were collected on a 4point scale ranging from 1 – “Never / Rarely” to 4 “Almost Always / Always.” Responses will be summed so that larger scores indicate higher impulsiveness. In the Rijeka panel, impulsiveness scores at T2, T3, and T6 will be mean averaged together to create a point estimate. **Sensation Seeking.** Sensation seeking was measured with Stephenson et al. (2003)’s brief 4-item composite at T2, T3 and T5 in the Zagreb panel and all waves (T2-T6) of the Rijeka panel. Example items included “I would like to explore strange places” and “I like new and exciting experiences, even if I have to break the rules.” Responses were measured on a 5-point scale ranging from 1 – “It does not relate to me at all” to 5 – “It relates to me completely.” Responses will be summed with higher scores indicating more sensation seeking. Sensation seeking measures will averaged across waves in both panels **Social Desirability.** Social desirability was measured with a short 11-item version of the Marlowe-Crowne Social Desirability scale (Reynolds, 1982) included in wave T5 in the Zagreb panel and waves T2 and T4 in the Rijeka panel. Example items included “I’m always willing to admit it when I make a mistake” and “I am sometimes irritated by people who ask favors of me.” Responses, which were collected using a yes/no scale, will be reverse coded and summed to create an ordinal scale with higher scores indicating higher social desirability. Social desirability scores across the two waves in the Rijeka panel will be averaged to create a single estimate.