Editing Sexual intercourse (section)

===Prevalence===
Penile–vaginal penetration is the most common form of sexual intercourse.<ref name="Alters"/><ref name="Carroll"/> Studies indicate that most heterosexual couples engage in vaginal intercourse nearly every sexual encounter.<ref name="Carroll"/> The National Survey of Sexual Health and Behavior (NSSHB) reported in 2010 that vaginal intercourse is "the most prevalent sexual behavior among men and women of all ages and ethnicities".<ref name="Carroll"/> Clint E. Bruess et al. stated that it "is the most frequently studied behavior" and is "often the focus of sexuality education programming for youth."<ref name="Bruess">{{cite book| author = Clint E. Bruess| author2 = Elizabeth Schroeder|title = Sexuality Education Theory and Practice| publisher = [[Jones & Bartlett Publishers]] | year = 2013 | page = 152 | access-date = December 5, 2014 |isbn = 978-1-4496-4928-9| url =https://books.google.com/books?id=WWFW6-kkAVoC&pg=PA152}}</ref> Weiten et al. said that it "is the most widely endorsed and practiced sexual act in our society."<ref name="Weiten3"/>

Regarding oral or anal intercourse, the CDC stated in 2009, "Studies indicate that oral sex is commonly practiced by sexually active male-female and same-gender couples of various ages, including adolescents."<ref name="CDC, oral sex"/> Oral sex is significantly more common than anal sex.<ref name="Weiten3"/><ref name="Aggleton 1"/> The 2010 NSSHB study reported that vaginal intercourse was practiced more than insertive anal intercourse among men, but that 13% to 15% of men aged 25 to 49 practiced insertive anal intercourse. Receptive anal intercourse was infrequent among men, with approximately 7% of men aged 14 to 94 years old having said that they were a receptive partner during anal intercourse. The study said that fewer women reported engaging in anal sex than other partnered sexual behaviors. It was estimated that 10% to 14% of women aged 18 to 39 years old practiced anal sex in the past 90 days, and that most of the women who engage in anal sex said they practiced it once a month or a few times a year.<ref name="Carroll"/>

===={{anchor|sexarche}}Age at first intercourse====
The prevalence of sexual intercourse has been compared cross-culturally. In 2003, Michael Bozon of the French [[Institut national d'études démographiques]] conducted a cross-cultural study titled "At what age do women and men have their first sexual intercourse?" In the first group of the contemporary cultures he studied, which included [[sub-Saharan Africa]] (listing [[Mali]], [[Senegal]] and [[Ethiopia]]), the data indicated that the age of men at sexual initiation in these societies is at later ages than that of women, but is often extra-marital; the study considered the [[Indian subcontinent]] to also fall into this group, though data was only available from [[Nepal]].<ref name="Bozon">{{cite journal |last=Bozon |first=Michael |year=2003 |title=At what age do women and men have their first sexual intercourse? World comparisons and recent trends |journal=Population and Societies |volume=391 |pages=1–4 |url=https://www.ined.fr/fichier/s_rubrique/247/english_391.en.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160304091955/https://www.ined.fr/fichier/s_rubrique/247/english_391.en.pdf |archive-date=March 4, 2016}}</ref><ref name="Caselli">{{cite book| author = Graziella Caselli| author2 = Guillaume Wunsch| author3 = Daniel Courgeau| author4 = Jacques Vallin| title = Demography&nbsp;– Analysis and Synthesis: A Treatise in Population| publisher = [[Academic Press]] | year = 2005 | pages = 490–501 | access-date = September 6, 2013 |isbn = 978-0-12-765660-1| url=https://books.google.com/books?id=nmgNXoiAiU4C&pg=PA491}}</ref> In the second group, the data indicated families encouraged daughters to delay marriage, and to abstain from sexual activity before that time. However, sons are encouraged to gain experience with older women or prostitutes before marriage. Age of men at sexual initiation in these societies is at lower ages than that of women; this group includes [[southern Europe|south European]] and Latin cultures (Portugal, Greece and Romania are noted) and such from [[Latin America]] (Brazil, [[Chile]], and the [[Dominican Republic]]). The study considered many Asian societies to also fall into this group, although matching data was only available from [[Thailand]].<ref name="Bozon" /><ref name="Caselli" /> In the third group, age of men and women at sexual initiation was more closely matched; there were two sub-groups, however. In non-Latin, Catholic countries (Poland and [[Lithuania]] are mentioned), age at sexual initiation was higher, suggesting later marriage and reciprocal valuing of male and female virginity. The same pattern of late marriage and reciprocal valuing of virginity was reflected in [[Singapore]] and [[Sri Lanka]]. The study considered China and Vietnam to also fall into this group, though data were not available.<ref name="Bozon" /><ref name="Caselli" /> In northern and eastern European countries, age at sexual initiation was lower, with both men and women involved in sexual intercourse before any union formation; the study listed Switzerland, Germany and the Czech Republic as members of this group.<ref name="Bozon" /><ref name="Caselli" />

Concerning United States data, tabulations by the [[National Center for Health Statistics]] report that the age of first sexual intercourse was 17.1 years for both males and females in 2010.<ref name="CDC abc_list_s">{{cite web|title=Key Statistics from the National Survey of Family Growth|access-date=February 9, 2013|publisher=[[Centers for Disease Control and Prevention]] (CDC)|url=https://www.cdc.gov/nchs/nsfg/abc_list_s.htm}}</ref> The CDC stated that 45.5 percent of girls and 45.7 percent of boys had engaged in sexual activity by 19 in 2002; in 2011, reporting their research from 2006 to 2010, they stated that 43% of American unmarried teenage girls and 42% of American unmarried teenage boys have ever engaged in sexual intercourse.<ref name="CDC statistics">{{cite web|title=Teenagers in the United States: Sexual Activity, Contraceptive Use, and Childbearing, 2006–2010 National Survey of Family Growth|access-date=December 26, 2012|publisher=[[Centers for Disease Control and Prevention]] (CDC)|url=https://www.cdc.gov/nchs/data/series/sr_23/sr23_031.pdf}}</ref> The CDC also reports that American girls will most likely lose their virginity to a boy who is 1 to 3 years older than they are.<ref name="CDC statistics"/> Between 1988 and 2002, the percentage of people in the U.S. who had sexual intercourse between the ages of 15 and 19 fell from 60 to 46 percent for never-married males, and from 51 to 46 percent for never-married females.<ref name="CDC sr23_024">{{cite web|title=Teenagers in the United States: Sexual Activity, Contraceptive Use, and Childbearing, 2002|access-date=February 9, 2013|publisher=[[Centers for Disease Control and Prevention]] (CDC)|url=https://www.cdc.gov/nchs/data/series/sr_23/sr23_024.pdf}}</ref>