Human sexuality is shaped by cultural context and historical period. In interaction with their culture and society, people learn and internalise sexuality's various expressions. Nordic sexual culture is different from that of the majority of other Western societies and cultures (Lewin et al., 2000; Kvalem & Tren, 2000). These differences in sexual culture are historically rooted, and connected to a well-integrated ideology about equality between individuals, and groups of individuals. Due to this historical development, there are probably less social restrictions upon adolescent sexuality, and in particular female sexuality, in the Nordic countries compared to other Western countries. Most adolescent boys and girls in Norway, as in the other Nordic countries have their first intercourse when they feel mature enough for sex (Tren & Kvalem, 1996a; Kvalem & Tren, 2000; Helmius, 2002). Feeling mature enough for sex is related to being in love, and having a committed relationship, which has lasted for some period of time, usually some months.
Representative, national surveys on sexual behavior in Europe and the US carried out during the past 10-15 years show that there has been a change in the reporting of age at coital debut (Bozon & Kontula, 1998; Teitler, 2002; Kontula, 2003). This change in age at first coitus was first noticed in the Nordic countries, then in several of the Western and Central European countries, and a generation thereafter in Southern and Eastern Europe. A comparison of coital debut age based on self-reports among European men shows little variation from country to country, and over time. The situation among women is different. Since the 1960s the reporting of coital debut age among Western European and US women fell by two to three years (Teitler, 2002). This does not alter the fact that in the majority of European countries, and in the USA (Sugar, 1995), boys still report having their coital debut at an earlier age than girls. Young Finnish, Swedish, Icelandic, Norwegian, Danish and German girls on the other hand, have reported to experience coitus at an earlier age than boys (Schmidt, Klausman, Dekker & Matthiesen, 1998; Edgardh, Lewin & Nilsson, 1999; Bozon & Kontula, 1998; Helmius, 2000; Kontula, 2003; Pedersen, Samuelsen & Wickstrom, 2004). Kontula (2003) points out that from a gender perspective two clear-cut profiles stand out. One is the double standard in the South of Europe, and the second is the egalitarianism of the North and a handful of other countries. In the south of Europe, premarital female sexuality is subject to more restrictions and social control compared to the Nordic countries.
Sexual experiences are collected step by step and the coitus is merely one of several experiences in this regard (Jakobsen, 1997; Edgardh et al, 1999; Schwartz, 1999; Gates & Sonenstein, 2000). In early childhood, children start masturbating (Sugar, 1995). Continuing their sexual exploration, children interact with other children and also engage in sexual games, such as playing "doctor" and "patient" (LeVay & Valent, 2003, p. 379). While playing these games, children can explore the body's secrets and start getting to know their own feeling of arousal and desire without the interference of adults. In their early teens, adolescents enter into couple relationships. In the Nordic context, society does not tolerate younger teenagers having extensive sexual experiences (Helmius, 2002). Sexual activity is more limited to non-coital activities such as kissing, touching of the body and genitals (Jakobsen, 1997; Pedersen & Samuelsen, 2003). Thus, one very important purpose of these early relationships is that the adolescents learn what it is like to be treated as part of a couple contrary to being single. Nordic sexual culture accepts that older teenagers have sexual intercourse and oral sex, provided they follow the love ideology and act responsibly and use contraception (Kvalem & Tren, 2000; Kvalem, 2002). Emotional and sexual engagements are important to the majority of Nordic adolescents when they enter into more mature forms of couple relationships (Tren & Kvalem, 1996a; Helmius, 2002). However, the issue of when coital and non-coital experiences occur for the first time remains relatively unexplored. Based on this background, the purpose of this paper is to estimate the median debut age of kissing, French kissing, touching of the body, masturbation, orgasm, coitus and oral sex in a longitudinal sample of Norwegian adolescents. When do they experience the different sexual activities for the first time? Are there gender differences in the reporting of sexual debut ages?
The data used to answer the research question was gathered using a longitudinal survey originally designed to evaluate the effect of a sex education intervention program. The intervention itself, its effects on contraceptive behavior, research design and dropout, has been described elsewhere (Tren, 2003). In 1999, a stratified sample of 74 compulsory schools, comprising 2717 pupils (in the 10th grade), was drawn at random from all compulsory schools in the county of Nordland in Northern Norway. Each school was randomly assigned to one of four conditions in a Solomon four-group design, that is as a randomized, prospective intervention study (Campbell & Stanley, 1966). Several schools declined to participate until they were told to which group they were assigned. By October 1999, a total of 54 schools were willing to participate in the study. With schools as units of randomization, this yields a response-rate of 73.0%. Before participation, all 2053 pupils from the 54 schools had to give their informed consent. Only 1183 adolescents, 533 boys and 650 girls, gave their consent (57.6%). As the schools are not allowed to hand out lists of their pupils' names, we are not able to make a comparison between participating and non-participating pupils on variables such as gender and academic performance.
Within the Solomon-Four-Group design, only half of the schools in the intervention and control groups received the pre-test (October 1999). All pupils were asked to fill out two post-test questionnaires, the first 6-7 months after the pre-test (May 2000) and the second 1 1/2 years after the pre-test (May 2001). The questionnaires at the baseline and the post-test 1 were handed out directly to the pupils in the classrooms. Each pupil filled out the questionnaire at home, and after filling it in the questionnaire was put in a sealed envelope. Teachers gathered the sealed envelopes they received from all the pupils in the class, and returned them collectively to the National Institute of Public Health by mail. At the second post-test, questionnaires were sent out directly to the pupils' home address, and returned by mail. On all three occasions one reminder was mailed after 2-3 weeks.
The mean age of the adolescents who responded to the pre-test questionnaire in 1999 was 14.9 years. At the first post-test in 2000 the mean age of the respondent was 15.5 years, and at the second posttest in 2001 the mean age was 16.4 years.
The questionnaire contained 99 questions, most of them previously used in other Norwegian, Swedish and...