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How old are young people when they start having sex? Unravelling the applicability of Cox proportional hazards regression



How old are young people when they start having sex? Although this question is important for educators and policymakers, its answer can easily mislead due to methodology that does not take into account age-censoring and generational trends. This study investigated whether 1-year birth-year cohorts can be jointly modeled by Cox proportional hazards regression to estimate sexual debut ages and to investigate age trends for different sexual behaviors.


We used pooled data from three Dutch periodic population-based surveys, for which 33,377 participants, born between 1980 and 2004, completed an online questionnaire.


Cox proportional hazards regression is appropriate if hazard changes over birth years appear proportionally similar among ages. The Dutch data shows such hazard changes for petting, oral sex, and sexual intercourse, but not for masturbation, French kissing, or manual sex. For sexual intercourse, the Cox model estimates can be interpreted as an approximate linear increase of 1 month in the median sexual debut age per birth-year cohort, resulting in an estimated debut age of 18.17 years in the current (2020) generation of Dutch adolescents.


If the assumptions are met, we recommend using the Cox regression modeling approach to estimate how old young people are when they start having sex, since this method yields precise and current debut ages by pooling information across birth-year cohorts without arbitrarily combining them in multiple-year groups. The age of first intercourse is increasing, so continuous sexuality education throughout high school is advisable, in addition to early sexuality education.

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  • Buhi ER, Goodson P (2007) Predictors of adolescent sexual behavior and intention: a theory-guided systematic review. J Adolesc Health 40:4–21

    Article  Google Scholar 

  • BZgA (Federal Centre for Health Education) (2010) Standards for sexuality education in Europe. BZgA, Cologne

  • Cavazos-Rehg PA, Krauss MJ, Spitznagel EL, Schootman M, Bucholz KK, Peipert JF et al (2009) Age of sexual debut among US adolescents. Contraception 80:158–162

    Article  Google Scholar 

  • Cha S, Masho SW, Mezuk B (2016) Age of sexual debut and cannabis use in the United States. Subst Use Misuse 51:439–448

    Article  Google Scholar 

  • De Graaf H, Vanwesenbeeck I, Meijer S, Woertman L, Meeus W (2009) Sexual trajectories during adolescence: relation to demographic characteristics and sexual risk. Arch Sex Behav 38(2):276–282

  • De Graaf H, Vanwesenbeeck I, Meijer S (2015) Educational differences in adolescents' sexual health: a pervasive phenomenon in a national dutch sample. The J Sex Res 52(7):747–757

  • De Graaf H, Verbeek M, Van den Borne M, Meijer S (2018) Offline and online sexual risk behavior among youth in the netherlands: findings from “sex under the age of 25”. Frontiers in Public Health 6

  • De Irala J, Osorio A, Ruiz-Canela M, Carlos S, Lopez-del Burgo C (2014) Informing youth about the age of sexual initiation using means or percentages. Health Commun 29:629–633

    Article  Google Scholar 

  • Doornwaard SM, Bickham DS, Rich M, Vanwesenbeeck I, Van den Eijnden RJJM, Ter Bogt TFM (2014) Sex-related online behaviors and adolescents’ body and sexual self-perceptions. Pediatrics 134:1103–1110

    Article  Google Scholar 

  • Epstein M, Furlong M, Kosterman R, Bailey JA, King KM, Vasilenko SA et al (2018) Adolescent age of sexual initiation and subsequent adult health outcomes. Am J Public Health 108:822–828

    Article  Google Scholar 

  • Ethier KA, Kann L, McManus T (2018) Sexual intercourse among high school students—29 states and United States overall, 2005–2015. Morb Mortal Wkly Rep 66:1393–1397

    Article  Google Scholar 

  • Finer LB (2007) Trends in premarital sex in the United States, 1954–2003. Public Health Rep 122:73–78

    Article  Google Scholar 

  • Golden RL, Furman W, Collibee C (2016) The risks and rewards of sexual debut. Dev Psychol 52:1913–1925

    Article  Google Scholar 

  • Halpern CT, Haydon AA (2012) Sexual timetables for oral-genital, vaginal, and anal intercourse: sociodemographic comparisons in a nationally representative sample of adolescents. Am J Public Health 102:1221–1228

    Article  Google Scholar 

  • Haydon AA, Herring AH, Prinstein MJ, Halpern CT (2012) Beyond age of first sex: patterns of emerging sexual behavior in adolescence and young adulthood. J Adolesc Health 50:456–463

    Article  Google Scholar 

  • Holway GV (2015) Vaginal and oral sex initiation timing: a focus on gender and race/ethnicity. Int J Sex Health 27:351–367

    Article  Google Scholar 

  • Ihongbe TOA, Cha S, Masho SW (2017) Age of sexual debut and physical dating violence victimization: sex differences among US high school students. J Sch Health 87:200–208

    Article  Google Scholar 

  • Lara LAS, Abda CHN (2016) Age at time of initial sexual intercourse and health of adolescent girls. J Pediatr Adolesc Gynecol 29:417–423

    Article  Google Scholar 

  • Lewis R, Tanton C, Mercer CH, Mitchell KR, Palmer M, Macdowall W, Wellings K (2017) Heterosexual practices among young people in Britain: evidence from three national surveys of sexual attitudes and lifestyles. J Adolesc Health 61:694e702

    Article  Google Scholar 

  • Liu G, Hariri S, Bradley H, Gottlieb SL, Leichliter JS, Markowitz LE (2015) Trends and patterns of sexual behaviors among adolescents and adults aged 14 to 59 years, United States. Sex Transm Dis 42:20–26

    CAS  Article  Google Scholar 

  • Madigan S, Ly A, Rash CL, Van Ouytsel J, Temple JR (2018) Prevalence of multiple forms of sexting behavior among youth: a systematic review and meta-analysis. JAMA Pediatr 172:327–335

    Article  Google Scholar 

  • Madkour SA, De Looze M, Maa P, Halpern CT, Farhat T, Ter Bogt TFM et al (2014) Macro-level age norms for the timing of sexual initiation and adolescents’ early sexual initiation in 17 European countries. J Adolesc Health 55:114–121

    Article  Google Scholar 

  • Mercer CH, Tanton C, Prah P, Erens B, Sonnenberg P, Clifton S et al (2013) Changes in sexual attitudes and lifestyles in Britain through the life course and over time: findings from the National Surveys of Sexual Attitudes and Lifestyles (Natsal). Lancet 382:1781–1794

    Article  Google Scholar 

  • Neville FG, McEachran J, Aleman-Diaz A, Whitehead R, Cosma A, Currie D, Currie C (2017) Trends in the sexual behaviour of 15-year olds in Scotland: 2002–14. Eur J Public Health 27:835–839

    Article  Google Scholar 

  • Osorio A, Lopez-del Burgo C, Carlos S, De Irala J (2017) The sooner, the worse? Association between earlier age of sexual initiation and worse adolescent health and well-being outcomes. Front Psychol 8:1298

    Article  Google Scholar 

  • Ramiro K, Windlin B, Reis M, Nic Gabhainn S, Jovic S, Matos MG et al (2015) Gendered trends in early and very early sex and condom use in 20 European countries from 2002 to 2010. Eur J Pub Health 25:65–68

    Article  Google Scholar 

  • Reis M, Ramiro L, Camacho I, Tomé G, De Matos MG (2018) Trends in Portuguese adolescents’ sexual behavior from 2002 to 2014: HBSC Portuguese study. Rev Port Sau Pub 36:32–40

    Google Scholar 

  • Rodgers RF, McLean SA, Paxton SJ (2015) Longitudinal relationships among internalization of the media ideal, peer social comparison, and body dissatisfaction: implications for the tripartite influence model. Dev Psychol 51:706–713

    Article  Google Scholar 

  • Sandfort TGM, Orr M, Hirsch J, Santelli J (2008) Long-term health correlates of timing of sexual debut: results from a national US study. Am J Public Health 98:155–161

    Article  Google Scholar 

  • Sawyer SM, Azzopardi PS, Wickremarathne D, Patton GC (2018) The age of adolescence. Lancet Child Adolesc Health 2:223–228

    Article  Google Scholar 

  • Ter Schure J (2020) Step-by-step assumptions underlying the use of Cox proportional hazards modeling for median sexual debut age estimation in age-censored data with generational trends.

  • Tornello SL, Riskind RF, Patterson C (2014) Sexual orientation and sexual and reproductive health among adolescent young women in the United States. J Adolesc Health 54:160–168

    Article  Google Scholar 

  • Twenge JM, Park H (2019) The decline in adult activities among U.S. adolescents, 1976–2016. Child Dev 90:638–654

    Article  Google Scholar 

  • Twenge JM, Martin GN, Spitzberg BH (2018) Trends in U.S. adolescents’ media use, 1976–2016: the rise of digital media, the decline of TV, and the (near) demise of print. Psychol Pop Media Cult 8:329–345

    Article  Google Scholar 

  • Vasilenko SE, Kugler KC, Rice CE (2016) Timing of first sexual intercourse and young adult health outcomes. J Adolesc Health 59:291–297

    Article  Google Scholar 

  • Ybarra ML, Mitchell KJ (2014) “Sexting” and its relation to sexual activity and sexual risk behavior in a national survey of adolescents. J Adolesc Health 55:757–764

    Article  Google Scholar 

  • Young H, Burke L, Gabhainn SN (2018) Sexual intercourse, age of initiation and contraception among adolescents in Ireland: findings from the Health Behaviour in School-aged Children (HBSC) Ireland study. BMC Public Health 18:362

    Article  Google Scholar 

  • Zaba B, Boerma T, Pisani E, Baptiste N (2002) Estimation of levels and trends in age at first sex from surveys using survival analysis. Chapel Hill, Carolina Population Center

  • Zaba B, Pisani E, Slaymaker E, Boerma JT (2004) Age at first sex: understanding recent trends in African demographic surveys. Sex Transm Infect 80:ii28–ii35

    Article  Google Scholar 

  • Zimmer-Gembeck MJ, Helfand M (2008) Ten years of longitudinal research on US adolescent sexual behavior: developmental correlates of sexual intercourse, and the importance of age, gender and ethnic background. Dev Rev 28:153–224

    Article  Google Scholar 

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Fifteen Municipal Health Services (GGDs) made a major contribution to the recruitment of a large database containing national as well as regional data.


This research was supported by a grant from the Dutch National Institute for Public Health and the Environment (RIVM), the Netherlands (grant number 323846).

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Authors and Affiliations



All authors contributed to the study conception and design. Hanneke de Graaf coordinated the study. Judith ter Schure performed the statistical analysis and participated in the interpretation of the results. Geneviève van Liere participated in data collection. All authors read and approved the final manuscript.

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Correspondence to Hanneke de Graaf.

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The authors declare that they have no conflict of interest.

Ethical approval

The MREC UMC Utrecht confirmed that the Medical Research Involving Human Subjects Act (WMO) does not apply to Sex under the age of 25, and therefore an official approval of this study by the MREC UMC Utrecht is not required under the WMO (reference number WAG/mb/16/013562).

Informed consent

For in-school youth, school boards provided active informed consent for participation of their students. In-school students and their parents provided passive informed assent and consent, respectively, where they were able to refuse voluntary participation. Out-of-school youth (≥17 years) provided active informed consent.

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de Graaf, H., ter Schure, J. & van Liere, G.A.F.S. How old are young people when they start having sex? Unravelling the applicability of Cox proportional hazards regression. J Public Health (Berl.) 30, 1873–1880 (2022).

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  • Population study
  • Sexual debut
  • Cox regression
  • Adolescence