A Campbell

Alfonso Osorio

CE Kaestle

Cristina López-del Burgo

D Wight

DT Halperin

EM Eshbaugh

G Rose

J Irala de

J Manlove

JE Rosenbaum

Jokin de Irala

KS Louie

L Avery

M Potts

Miguel Ruiz-Canela

Q Ma

S Vaccarella

Silvia Carlos

English

PubMed

Irala, J. (Jokin) de

Osorio, A. (Alfonso)

Carlos, S. (Silvia)

Ruiz-Canela, M. (Miguel)

Lopez-del-Burgo, C. (Cristina)

Dadun, University of Navarra

LETTER TO THE EDITORMean Age of First Sex: Do They Know What We Mean?Jokin de Irala • Alfonso Osorio • Silvia Carlos •Miguel Ruiz-Canela • Cristina Lo´pez-del BurgoPublished online: 27 May 2011 The Author(s) 2011. This article is published with open access at Springerlink.comEarly age at first sexual intercourse is a particularly importantvariable for public health policy makers. It is associated withspecific unhealthy behaviors, such as having unprotected sex onfirst sexual intercourse,condommisuseorhavingmultiple (con-current or lifetime) partners (Kaestle, Halpern, Miller, & Ford,2005; Louie et al., 2009). These can lead to higher rates of sex-ually transmitted infections (STIs), teenage pregnancy, andadverse psychological consequences, such as feelings of disap-pointment and regret (Campbell, 2008; CDC, 2008; Eshbaugh& Gute, 2008; Ma et al., 2009; Vaccarella et al., 2006; Wightet al., 2008).In the light of the role played by the delay of first sexualintercourse and mutual monogamy in curtailing STI epidemics(Halperin et al., 2011; Potts et al., 2008), the Joint United NationsProgram on HIV/AIDS (UNAIDS) has introduced changes in itsyearly reports on the global AIDS epidemic: in addition to con-dom use, they now report age of sexual initiation and multiplepartnerships in different countries as a means of more compre-hensively following up on all the determinants of the epidemic(UNAIDS, 2006, 2008).However, the information concerningageof sexual initiationcan be conveyed in different ways. For instance, UNAIDS usu-ally reports the ‘‘proportion, among 15–19-year-olds, havinghad sex byage 15’’(UNAIDS, 2008) whereas other sources usethe ‘‘mean age at first sexual intercourse’’ alone or in combi-nation with‘‘proportions having already had sex at given ages’’(Avery & Lazdane, 2008; Kaestle et al., 2005; Manlove, Ikra-mullah, Mincieli, Holcombe, & Danish, 2009; Rosenbaum,2009).Averageagesatfirst sexual intercourse lackprecision indescribing the extent of sexual experience at different ages.They are sensitive toextreme values and sensitive to the rangesof ages of the persons included in the survey. For example, aplausible wrong interpretation of the statement that‘‘the meanageofsexual initiation is15 years’’is that‘‘mostyouth’’aged15are having sex when, in fact, the contrary may be true. Averageages at first sexual intercourse, obtained from published epi-demiological studies about sexuality, are often conveyed bythe media in such a way that it does not necessarily grasp thesubtleties entailed in such data. The targets of media, such asthe general population and indeed young people themselves,can, in turn, be misled. Sentences derived from average datasuch as this one—‘‘compared with previous generations,young people (16–20 year-olds) were having intercourse forthe first time at an earlier age, on average at 16.5 years of age’’(Avery & Lazdane, 2008)—leave the facts as to how manyfrom these age groups have, in fact, had sex unspecified. Theseconfusing interpretations of epidemiological data create defi-nite impressions that can be misleading and thus may hinderpublic health and educational interventions that are trying todelay sexual initiation in youth (Halperin et al., 2004). As Rose(1992) affirmed years ago, ‘‘It doesn’t make much sense toexpect that individuals will behave differently from their peers;J. de Irala (&)  S. Carlos  C. Lo´pez-del BurgoPreventive Medicine and Public Health, School of Medicine,University of Navarra, 31080 Pamplona, Spaine-mail: jdeirala@unav.esA. OsorioDepartment of Education, University of Navarra, Pamplona, SpainM. Ruiz-CanelaDepartment of Biomedical Humanities, University of Navarra,Pamplona, SpainJ. de Irala  A. Osorio  S. Carlos  M. Ruiz-Canela C. Lo´pez-del BurgoInstitute of Culture and Society, University of Navarra,Pamplona, Spain123Arch Sex Behav (2011) 40:853–855DOI 10.1007/s10508-011-9779-4it is more appropriate to change the general norms of behaviorand the circumstances that facilitate these changes.’’Data from an ongoing international study which examineswhat youth think and feel about relationships, love, and sexu-ality were used to show that this confusion is indeed possible(Project YOURLIFE). Specific details on the data collectionprocess for this project are described elsewhere (de Irala et al.,2009). Briefly, project YOURLIFE is a cross-sectional surveythat is being implemented in different countries through amulti-stage sampling of clusters representative of public andprivate schools within participating countries. A question-naire was used to gather information on sociodemographicdata, characteristics of the group of friends, use of free time,access and exposure to media, feelings, opinions, and informa-tion sources on relationships, love, and sexuality, and life goals.In order to compare ‘‘mean’’ages of first sexual intercourseand ‘‘proportions’’ of youth sexually experienced at differentages, data from El Salvador, Peru, and Spain were used (N =7011; see Table 1). Country specific‘‘mean ages of sexual ini-tiation’’ are presented together with their corresponding ‘‘pro-portions of youth having had sex at different ages’’ in order toshow how different interpretations might be conveyed whenusing one or the other. Mean ages were estimated using threedifferent age ranges to allow for a sensitivity analysis: (1) theage ranges actually available in each study site, (2) the closestpossible ranges to the15–19rangeusedbyUNAIDS,and(3) theage range thatwascommonto the threecountrieswhosedataweused.In all the estimations of mean age of first sexual intercoursepresented in the table, the actual mean value is compatible withthe fact that the majority of youth whose ages are close to thatmean value have not had sex yet. The use of means could, there-fore, be conveying a wrong message. In fact, less than 25% ofyouth with ages close to the mean were sexually initiated in allcountries of the table shown. The mean age of first sexual inter-course was obviously estimated solely using subjects who havealready had sexual intercourse whereas the proportion of youththat were sexually initiated use all youth in each age group as thedenominator. Inallcases, themostaccurateandleastmisleadinginformation to know the extentof sexual initiation at a given ageseems to be the percentage sexually active at different ages.Some authors use mean ages of sexual initiation with shorterage intervals (Ma et al., 2009). This has the advantage of obtain-ing mean ages that are closer to the ages examined in the ageinterval but does not eliminate the misleading effect of convey-ingthat‘‘most’’youthofthoseageshavehadsexwhenthecontraryTable 1 Age of first sexual intercourse of youth from El Salvador, Peru, and Spain (Project YOURLIFE) using different statisticsCountry Percent sexually activeat different agesaMean and Median age of first sexual intercourse using different rangesbAge (%) Range of each study venue(age range)Range closest to 15–19c(age range)Range common to threecountries (age range)El Salvador(N = 2,810)13 (6.7)14 (13.8)15 (20.9)16 (26.6)17 (32.0)18 (38.0)19 (45.5)(13–19)Mean: 14.8Median: 15(15–19)Mean: 15.2Median: 15(16–18)Mean: 15.3Median: 15Peru (N = 3,399) 13 (4.4)14 (9.6)15 (17.0)16 (21.4)17 (29.4)18 (40.0)(13–18)Mean: 14.3Median: 15(15–18)Mean: 14.5Median: 15(16–18)Mean: 14.8Median: 15Spain (N = 802) 16 (21.7)17 (34.8)18 (62.9)19 (78.0)20 (79.5)(16–20)Mean: 16.3Median: 16(16–19)Mean: 16.2Median: 16(16–18)Mean: 15.8Median: 16a Percent calculated at each age group using all youth in the denominator (whether sexually experienced or not)b Estimated solely using youth who already have had sexual intercoursec Range of 15–19 typically used by UNAIDS854 Arch Sex Behav (2011) 40:853–855123is true, as is the case with our Spanish data in the table, with shortage intervals.The extensive use of mean age of sexual initiation in thescientific literature and consequently in the media suggests thatthe potential for misleading interpretations is not being ade-quately taken into account. Studies that use mean age of sexualinitiation usually use age ranges that do not take into accountthose who have first sex at older ages or who never have had sexat all. This essentially biases the interpretation of such means.The data presented in the table clearly show that the percent-ageofyouthsexuallyactivecanbequite lowatages thatarecloseto the mean age of sexual initiation and confirm that the use ofthis mean can be misleading and that misinterpretation of datais, indeed, quite plausible when using such average ages of sex-ual initiation. This finding was robust and remained unchangedwhen different age ranges were used to estimate the means. Thedata used to estimate these percentages and means are not artifi-cial andcomefromdifferent countries usingsimilar surveymeth-odologies. Furthermore, these data were representative of thestudents from the respective countries. However, the percent-age of youth sexually active will always tend to be quite low atages thatareclose to themeanageoffirst sexual intercoursewithwhatever data commonly used in epidemiological studies tar-getingyouth.Thedistributionof themeanageoffirst sexual inter-course is always skewed in the context of such studies. The meanage of first sexual intercourse will, therefore, never be consistentwith‘‘most youth close to that age having already had sex.’’To our knowledge, no one has shown using real data that theuse of mean age of sexual initiation can be misleading, espe-cially when this information is portrayed without also specify-ing the percentage sexually active at each age. A more precisedepiction of trends and displaying percentages to target audi-ences provides the clearest picture and can be of crucial help tohealth policy makers and health education managers who aretrying to convey the importance of delaying sexual initiationamong youth. We therefore encourage the use of the percentageofyouth, atdifferentages,whohavealready initiatedsexual rela-tionships instead of the use of averages. This will reduce con-fusion, help avoid erroneous interpretations, and provide a muchneededadditionalsourceofsupport toyoungpeople,allofwhichin turn gives such public health policies a better chance of suc-ceeding.Acknowledgments This work was partially supported by IntermediaConsulting (Italy),Concultura (El Salvador), the UniversityofPiura (Peru),theUniversityofNavarraandtheGovernmentofNavarra [project24/2007](Spain). We thank Matthew Hanley, for reviewing the English version ofthis letter, and Professor Miguel Delgado Rodrı´guez for his insights.Open Access This article is distributed under the terms of the CreativeCommonsAttributionNoncommercialLicensewhichpermitsanynoncom-mercial use, distribution, and reproduction in any medium, provided theoriginal author(s) and source are credited.ReferencesAvery, L., & Lazdane, G. (2008). What do we know about sexual andreproductive health of adolescents in Europe? European Journal ofContraception Reproductive Health Care, 13, 58–70.Campbell, A. (2008). The morning after the night before: Affective reac-tions to one-night stands among mated and unmated women andmen. Human Nature, 19, 157–173.Centers for Disease Control and Prevention. (2008). Nationally repre-sentative CDC study finds 1 in 4 teenage girls has a sexually trans-mitted disease. Retrieved June 29, 2010 from www.cdc.gov/stdconference/2008/press/release-11march2008.htm.de Irala, J., Osorio, A., Lo´pez del Burgo, C., Belen, V. A., de Guzman, F.O., Calatrava, M., et al. (2009). Relationships, love and sexuality:What the Filipino teens think and feel. BMC Public Health, 9, 282.Eshbaugh, E. M., & Gute, G. (2008). Hookups and sexual regret amongcollege women. Journal of Social Psychology, 148, 77–89.Halperin, D. T., Mugurungi, O., Hallett, T. B., Muchini, B., Campbell,B., Magure, T., et al. (2011). A surprising prevention success: Whydid the HIV epidemic decline in Zimbabwe? PLoS Medicine, 8(2),e1000414.Halperin, D. T., Steiner, M. J., Cassell, M. M., Green, E. C., Hearst, N.,Kirby, D., et al. (2004). The time has come for common ground onpreventing sexual transmission of HIV. Lancet, 364, 1913–1915.Kaestle, C. E., Halpern, C. T., Miller, W. C., & Ford, C. A. (2005).Young age at first sexual intercourse and sexually transmitted infec-tions in adolescents and young adults. American Journal of Epi-demiology, 161, 774–780.Louie, K. S., de Sanjose, S., Diaz, M., Castellsague, X., Herrero, R.,Meijer, C. J., et al. (2009). Early age at first sexual intercourse andearly pregnancy are risk factors for cervical cancer in developingcountries British. Journal of Cancer, 100, 1191–1197.Ma, Q., Ono-Kihara, M., Cong, L., Xu, G., Pan, X., Zamani, S., et al.(2009). Early initiation of sexual activity: A risk factor for sexu-ally transmitted diseases, HIV infection, and unwanted pregnancyamong university students in China. BMC Public Health, 9, 111.Manlove, J., Ikramullah, E., Mincieli, L., Holcombe, E., & Danish, S.(2009). Trends in sexual experience, contraceptive use, and teenagechildbearing:1992–2002.JournalofAdolescentHealth,44, 413–423.Potts, M., Halperin, D. T., Kirby, D., Swidler, A., Marseille, E., Klausner,J. D., et al. (2008). Reassessing HIV prevention. Science, 320, 749–750.Rose, G. (1992). The strategy of preventive medicine. Oxford: OxfordUniversity Press.Rosenbaum, J. E. (2009). Patient teenagers? A comparison of the sexualbehavior of virginity pledgers and matched nonpledgers. Pediat-rics, 123(1), e110–e120.UNAIDS. (2006). 2006 Report on the global AIDS epidemic. RetrievedJune 29, 2010, from http://www.unaids.org/en/KnowledgeCentre/HIVData/GlobalReport/2006/default.asp.UNAIDS. (2008). 2008 Report on the global AIDS epidemic. RetrievedJune 29, 2010, from http://www.unaids.org/en/KnowledgeCentre/HIVData/GlobalReport/2008/2008_Global_report.asp.Vaccarella, S., Franceschi, S., Herrero, R., Munoz, N., Snijders, P. J.,Clifford, G. M., et al. (2006). Sexual behavior, condom use, andhuman papillomavirus: Pooled analysis of the IARC human pap-illomavirus prevalence surveys. Cancer Epidemiology, Biomark-ers and Prevention, 15, 326–333.Wight, D., Parkes, A., Strange, V., Allen, E., Bonell, C., & Henderson,M. (2008). The quality of young people’s heterosexual relation-ships: A longitudinal analysis of characteristics shaping subjectiveexperience. Perspectives on Sexual and Reproductive Health, 40,226–237.Arch Sex Behav (2011) 40:853–855 855123

Mean age of first sex. Do they know what we mean?

Carlos-Chillerón, S. (Silvia)

Universidad de Navarra

Springer - Publisher Connector

LETTER TO THE EDITOR
Mean Age of First Sex: Do They Know What We Mean?
Jokin de Irala • Alfonso Osorio • Silvia Carlos •
Miguel Ruiz-Canela • Cristina Lo´pez-del Burgo
Published online: 27 May 2011
 The Author(s) 2011. This article is published with open access at Springerlink.com
Early age at first sexual intercourse is a particularly important
variable for public health policy makers. It is associated with
specific unhealthy behaviors, such as having unprotected sex on
first sexual intercourse,condommisuseorhavingmultiple (con-
current or lifetime) partners (Kaestle, Halpern, Miller, & Ford,
2005; Louie et al., 2009). These can lead to higher rates of sex-
ually transmitted infections (STIs), teenage pregnancy, and
adverse psychological consequences, such as feelings of disap-
pointment and regret (Campbell, 2008; CDC, 2008; Eshbaugh
& Gute, 2008; Ma et al., 2009; Vaccarella et al., 2006; Wight
et al., 2008).
In the light of the role played by the delay of first sexual
intercourse and mutual monogamy in curtailing STI epidemics
(Halperin et al., 2011; Potts et al., 2008), the Joint United Nations
Program on HIV/AIDS (UNAIDS) has introduced changes in its
yearly reports on the global AIDS epidemic: in addition to con-
dom use, they now report age of sexual initiation and multiple
partnerships in different countries as a means of more compre-
hensively following up on all the determinants of the epidemic
(UNAIDS, 2006, 2008).
However, the information concerningageof sexual initiation
can be conveyed in different ways. For instance, UNAIDS usu-
ally reports the ‘‘proportion, among 15–19-year-olds, having
had sex byage 15’’(UNAIDS, 2008) whereas other sources use
the ‘‘mean age at first sexual intercourse’’ alone or in combi-
nation with‘‘proportions having already had sex at given ages’’
(Avery & Lazdane, 2008; Kaestle et al., 2005; Manlove, Ikra-
mullah, Mincieli, Holcombe, & Danish, 2009; Rosenbaum,
2009).Averageagesatfirst sexual intercourse lackprecision in
describing the extent of sexual experience at different ages.
They are sensitive toextreme values and sensitive to the ranges
of ages of the persons included in the survey. For example, a
plausible wrong interpretation of the statement that‘‘the mean
ageofsexual initiation is15 years’’is that‘‘mostyouth’’aged15
are having sex when, in fact, the contrary may be true. Average
ages at first sexual intercourse, obtained from published epi-
demiological studies about sexuality, are often conveyed by
the media in such a way that it does not necessarily grasp the
subtleties entailed in such data. The targets of media, such as
the general population and indeed young people themselves,
can, in turn, be misled. Sentences derived from average data
such as this one—‘‘compared with previous generations,
young people (16–20 year-olds) were having intercourse for
the first time at an earlier age, on average at 16.5 years of age’’
(Avery & Lazdane, 2008)—leave the facts as to how many
from these age groups have, in fact, had sex unspecified. These
confusing interpretations of epidemiological data create defi-
nite impressions that can be misleading and thus may hinder
public health and educational interventions that are trying to
delay sexual initiation in youth (Halperin et al., 2004). As Rose
(1992) affirmed years ago, ‘‘It doesn’t make much sense to
expect that individuals will behave differently from their peers;
J. de Irala (&)  S. Carlos  C. Lo´pez-del Burgo
Preventive Medicine and Public Health, School of Medicine,
University of Navarra, 31080 Pamplona, Spain
e-mail: jdeirala@unav.es
A. Osorio
Department of Education, University of Navarra, Pamplona, Spain
M. Ruiz-Canela
Department of Biomedical Humanities, University of Navarra,
Pamplona, Spain
J. de Irala  A. Osorio  S. Carlos  M. Ruiz-Canela 
C. Lo´pez-del Burgo
Institute of Culture and Society, University of Navarra,
Pamplona, Spain
123
Arch Sex Behav (2011) 40:853–855
DOI 10.1007/s10508-011-9779-4
it is more appropriate to change the general norms of behavior
and the circumstances that facilitate these changes.’’
Data from an ongoing international study which examines
what youth think and feel about relationships, love, and sexu-
ality were used to show that this confusion is indeed possible
(Project YOURLIFE). Specific details on the data collection
process for this project are described elsewhere (de Irala et al.,
2009). Briefly, project YOURLIFE is a cross-sectional survey
that is being implemented in different countries through a
multi-stage sampling of clusters representative of public and
private schools within participating countries. A question-
naire was used to gather information on sociodemographic
data, characteristics of the group of friends, use of free time,
access and exposure to media, feelings, opinions, and informa-
tion sources on relationships, love, and sexuality, and life goals.
In order to compare ‘‘mean’’ages of first sexual intercourse
and ‘‘proportions’’ of youth sexually experienced at different
ages, data from El Salvador, Peru, and Spain were used (N =
7011; see Table 1). Country specific‘‘mean ages of sexual ini-
tiation’’ are presented together with their corresponding ‘‘pro-
portions of youth having had sex at different ages’’ in order to
show how different interpretations might be conveyed when
using one or the other. Mean ages were estimated using three
different age ranges to allow for a sensitivity analysis: (1) the
age ranges actually available in each study site, (2) the closest
possible ranges to the15–19rangeusedbyUNAIDS,and(3) the
age range thatwascommonto the threecountrieswhosedatawe
used.
In all the estimations of mean age of first sexual intercourse
presented in the table, the actual mean value is compatible with
the fact that the majority of youth whose ages are close to that
mean value have not had sex yet. The use of means could, there-
fore, be conveying a wrong message. In fact, less than 25% of
youth with ages close to the mean were sexually initiated in all
countries of the table shown. The mean age of first sexual inter-
course was obviously estimated solely using subjects who have
already had sexual intercourse whereas the proportion of youth
that were sexually initiated use all youth in each age group as the
denominator. Inallcases, themostaccurateandleastmisleading
information to know the extentof sexual initiation at a given age
seems to be the percentage sexually active at different ages.
Some authors use mean ages of sexual initiation with shorter
age intervals (Ma et al., 2009). This has the advantage of obtain-
ing mean ages that are closer to the ages examined in the age
interval but does not eliminate the misleading effect of convey-
ingthat‘‘most’’youthofthoseageshavehadsexwhenthecontrary
Table 1 Age of first sexual intercourse of youth from El Salvador, Peru, and Spain (Project YOURLIFE) using different statistics
Country Percent sexually active
at different agesa
Mean and Median age of first sexual intercourse using different rangesb
Age (%) Range of each study venue
(age range)
Range closest to 15–19c
(age range)
Range common to three
countries (age range)
El Salvador
(N = 2,810)
13 (6.7)
14 (13.8)
15 (20.9)
16 (26.6)
17 (32.0)
18 (38.0)
19 (45.5)
(13–19)
Mean: 14.8
Median: 15
(15–19)
Mean: 15.2
Median: 15
(16–18)
Mean: 15.3
Median: 15
Peru (N = 3,399) 13 (4.4)
14 (9.6)
15 (17.0)
16 (21.4)
17 (29.4)
18 (40.0)
(13–18)
Mean: 14.3
Median: 15
(15–18)
Mean: 14.5
Median: 15
(16–18)
Mean: 14.8
Median: 15
Spain (N = 802) 16 (21.7)
17 (34.8)
18 (62.9)
19 (78.0)
20 (79.5)
(16–20)
Mean: 16.3
Median: 16
(16–19)
Mean: 16.2
Median: 16
(16–18)
Mean: 15.8
Median: 16
a Percent calculated at each age group using all youth in the denominator (whether sexually experienced or not)
b Estimated solely using youth who already have had sexual intercourse
c Range of 15–19 typically used by UNAIDS
854 Arch Sex Behav (2011) 40:853–855
123
is true, as is the case with our Spanish data in the table, with short
age intervals.
The extensive use of mean age of sexual initiation in the
scientific literature and consequently in the media suggests that
the potential for misleading interpretations is not being ade-
quately taken into account. Studies that use mean age of sexual
initiation usually use age ranges that do not take into account
those who have first sex at older ages or who never have had sex
at all. This essentially biases the interpretation of such means.
The data presented in the table clearly show that the percent-
ageofyouthsexuallyactivecanbequite lowatages thatareclose
to the mean age of sexual initiation and confirm that the use of
this mean can be misleading and that misinterpretation of data
is, indeed, quite plausible when using such average ages of sex-
ual initiation. This finding was robust and remained unchanged
when different age ranges were used to estimate the means. The
data used to estimate these percentages and means are not artifi-
cial andcomefromdifferent countries usingsimilar surveymeth-
odologies. Furthermore, these data were representative of the
students from the respective countries. However, the percent-
age of youth sexually active will always tend to be quite low at
ages thatareclose to themeanageoffirst sexual intercoursewith
whatever data commonly used in epidemiological studies tar-
getingyouth.Thedistributionof themeanageoffirst sexual inter-
course is always skewed in the context of such studies. The mean
age of first sexual intercourse will, therefore, never be consistent
with‘‘most youth close to that age having already had sex.’’
To our knowledge, no one has shown using real data that the
use of mean age of sexual initiation can be misleading, espe-
cially when this information is portrayed without also specify-
ing the percentage sexually active at each age. A more precise
depiction of trends and displaying percentages to target audi-
ences provides the clearest picture and can be of crucial help to
health policy makers and health education managers who are
trying to convey the importance of delaying sexual initiation
among youth. We therefore encourage the use of the percentage
ofyouth, atdifferentages,whohavealready initiatedsexual rela-
tionships instead of the use of averages. This will reduce con-
fusion, help avoid erroneous interpretations, and provide a much
neededadditionalsourceofsupport toyoungpeople,allofwhich
in turn gives such public health policies a better chance of suc-
ceeding.
Acknowledgments This work was partially supported by Intermedia
Consulting (Italy),Concultura (El Salvador), the UniversityofPiura (Peru),
theUniversityofNavarraandtheGovernmentofNavarra [project24/2007]
(Spain). We thank Matthew Hanley, for reviewing the English version of
this letter, and Professor Miguel Delgado Rodrı´guez for his insights.
Open Access This article is distributed under the terms of the Creative
CommonsAttributionNoncommercialLicensewhichpermitsanynoncom-
mercial use, distribution, and reproduction in any medium, provided the
original author(s) and source are credited.
References
Avery, L., & Lazdane, G. (2008). What do we know about sexual and
reproductive health of adolescents in Europe? European Journal of
Contraception Reproductive Health Care, 13, 58–70.
Campbell, A. (2008). The morning after the night before: Affective reac-
tions to one-night stands among mated and unmated women and
men. Human Nature, 19, 157–173.
Centers for Disease Control and Prevention. (2008). Nationally repre-
sentative CDC study finds 1 in 4 teenage girls has a sexually trans-
mitted disease. Retrieved June 29, 2010 from www.cdc.gov/std
conference/2008/press/release-11march2008.htm.
de Irala, J., Osorio, A., Lo´pez del Burgo, C., Belen, V. A., de Guzman, F.
O., Calatrava, M., et al. (2009). Relationships, love and sexuality:
What the Filipino teens think and feel. BMC Public Health, 9, 282.
Eshbaugh, E. M., & Gute, G. (2008). Hookups and sexual regret among
college women. Journal of Social Psychology, 148, 77–89.
Halperin, D. T., Mugurungi, O., Hallett, T. B., Muchini, B., Campbell,
B., Magure, T., et al. (2011). A surprising prevention success: Why
did the HIV epidemic decline in Zimbabwe? PLoS Medicine, 8(2),
e1000414.
Halperin, D. T., Steiner, M. J., Cassell, M. M., Green, E. C., Hearst, N.,
Kirby, D., et al. (2004). The time has come for common ground on
preventing sexual transmission of HIV. Lancet, 364, 1913–1915.
Kaestle, C. E., Halpern, C. T., Miller, W. C., & Ford, C. A. (2005).
Young age at first sexual intercourse and sexually transmitted infec-
tions in adolescents and young adults. American Journal of Epi-
demiology, 161, 774–780.
Louie, K. S., de Sanjose, S., Diaz, M., Castellsague, X., Herrero, R.,
Meijer, C. J., et al. (2009). Early age at first sexual intercourse and
early pregnancy are risk factors for cervical cancer in developing
countries British. Journal of Cancer, 100, 1191–1197.
Ma, Q., Ono-Kihara, M., Cong, L., Xu, G., Pan, X., Zamani, S., et al.
(2009). Early initiation of sexual activity: A risk factor for sexu-
ally transmitted diseases, HIV infection, and unwanted pregnancy
among university students in China. BMC Public Health, 9, 111.
Manlove, J., Ikramullah, E., Mincieli, L., Holcombe, E., & Danish, S.
(2009). Trends in sexual experience, contraceptive use, and teenage
childbearing:1992–2002.JournalofAdolescentHealth,44, 413–423.
Potts, M., Halperin, D. T., Kirby, D., Swidler, A., Marseille, E., Klausner,
J. D., et al. (2008). Reassessing HIV prevention. Science, 320, 749–
750.
Rose, G. (1992). The strategy of preventive medicine. Oxford: Oxford
University Press.
Rosenbaum, J. E. (2009). Patient teenagers? A comparison of the sexual
behavior of virginity pledgers and matched nonpledgers. Pediat-
rics, 123(1), e110–e120.
UNAIDS. (2006). 2006 Report on the global AIDS epidemic. Retrieved
June 29, 2010, from http://www.unaids.org/en/KnowledgeCentre/
HIVData/GlobalReport/2006/default.asp.
UNAIDS. (2008). 2008 Report on the global AIDS epidemic. Retrieved
June 29, 2010, from http://www.unaids.org/en/KnowledgeCentre/
HIVData/GlobalReport/2008/2008_Global_report.asp.
Vaccarella, S., Franceschi, S., Herrero, R., Munoz, N., Snijders, P. J.,
Clifford, G. M., et al. (2006). Sexual behavior, condom use, and
human papillomavirus: Pooled analysis of the IARC human pap-
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Mean Age of First Sex: Do They Know What We Mean?

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