ORIGINAL PAPER

Changes in/uni00A0Penile-Vaginal Intercourse Frequency and/uni00A0Sexual Repertoire from/uni00A02009 to/uni00A02018: Findings from/uni00A0the/uni00A0National Survey of/uni00A0Sexual Health and/uni00A0Behavior

Debby/uni00A0Herbenick 1 /uni00A0· Molly/uni00A0Rosenberg 1,2 /uni00A0· Lilian/uni00A0Golzarri-Arroyo 3 /uni00A0· J./uni00A0Dennis/uni00A0Fortenberry 1,4 /uni00A0· Tsung-chieh/uni00A0Fu 1

Received: 27 March 2021 / Revised: 30 July 2021 / Accepted: 2 August 2021 / Published online: 19 November 2021 © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021

Abstract

Solo and partnered sexual behaviors are relevant to health, well-being, and relationships. Recent research shows that sexual frequency has declined in the U.S. and in other countries; however, measurement has been imprecise. We used data from 14- to 49-year-old participants in the 2009 and 2018 waves of the National Survey of Sexual Health and Behavior (NSSHB), a confidential U.S. nationally representative survey that is conducted online. We aimed to: (1) assess changes in frequency of past-year penile-vaginal intercourse and (2) examine combinations of past-year sexual behaviors for each of the two waves. We hypothesized that we would observe lower frequency of penile-vaginal intercourse (PVI) from 2009 to 2018 and that we would observe greater engagement in sexual repertoires involving non-coital partnered behaviors (e.g., partnered masturbation, oral sex) in 2018 as compared to 2009. Participants were 4155 individuals from the 2009 NSSHB (Adolescents: 406 females, 414 males; Adults: 1591 women, 1744 men) and 4547 individuals from the 2018 NSSHB (Adolescents: 416 females, 411 males; Adults: 2007 women, 1713 men). Compared to adult participants in the 2009 NSSHB, adults in the 2018 NSSHB were significantly more likely to report no PVI in the prior year (28% in 2018 vs. 24% in 2009). A similar difference in proportions reporting no PVI in the prior year was observed among 14-17-year-old adolescents (89% in 2018 vs. 79% in 2009). Additionally, for both adolescents and adults, we observed decreases in all modes of partnered sex queried and, for adolescents, decreases in solo masturbation.

Keywords Sexual frequency/uni00A0· Sexual repertoire/uni00A0· National Survey of Sexual Health and Relationships/uni00A0· Penile-vaginal intercourse frequency/uni00A0· Masturbation

Introduction

Solo and partnered sexual behavior contribute to mental and physical health, sexual and gender identity development, reproduction, cognitive function, happiness, sexual pleasure

• * Debby Herbenick debby@iu.edu
• 1 The Center for/uni00A0Sexual Health Promotion, Indiana University School of/uni00A0Public Health, Room 116, Indiana University, Bloomington, IN/uni00A047405, USA
• 2 Department of/uni00A0Epidemiology and/uni00A0Biostatistics, Indiana University School of/uni00A0Public Health Indiana University, Bloomington, IN, USA
• 3 Biostatistics Consulting Center, Indiana University School of/uni00A0Public Health Indiana University, Bloomington, IN, USA
• 4 Division of/uni00A0Adolescent Medicine, Indiana University School of/uni00A0Medicine, Indiana University, Indianapolis, IN, USA

and well-being, interpersonal relationships, and quality of life (e.g., Kaestle & Allen, 2011; Levin, 2007; Lindau et/uni00A0al., 2007; Mitchell et/uni00A0al., 2013; Schmiedeberg et/uni00A0al., 2017; Sprott & Benoit Hadcock, 2018; World Health Organization, 2006). Also, people who are more satisfied in their romantic/sexual relationships and/or who are healthier and lack sleep difficulties tend to be more sexually active (e.g., Field et/uni00A0al., 2013; Hess et/uni00A0al., 2009; Lindau & Gavrilova, 2010; McNulty et/uni00A0al., 2016).

Declines in/uni00A0Sexual Frequency

Recently, studies from the USA, the UK, Australia, Germany, and Japan have observed declines over time in partnered sexual activity. Researchers have expressed concern about such declines, given the consequences on human fertility and relationship happiness as well as what potential declines in partnered sexual frequency may reflect about

the influences of social media platforms, environmental influences on people's hormones, and overall changes to human connection and intimacy (e.g., Twenge et/uni00A0al., 2017; Wellings et/uni00A0al., 2019). Despite the consistency of these cross-national findings, multiple interpretations for these shifts have been proposed, including the idea that the decline in frequency may be associated with changes in sexual repertoire-increased quality of sex in the context of decreased frequency (e.g., Herbenick et/uni00A0al., 2010b; Richters et/uni00A0al., 2006) For example, using data from US adults ages 18 and older in General Social Survey (GSS) waves conducted between 1989 and 2014, Twenge et/uni00A0al. (2017) found that sexual frequency had declined over time-particularly among midlife cohorts and individuals with school-aged children. Strengths of the GSS include its robust sample size, methodology, and ability to support comparisons across decades; however, these strengths are tempered by the broad coverage of the GSS and thus the little space allocated to sexual behavior assessment. The GSS item used for the Twenge et/uni00A0al. (2017) analysis asks, 'About how often did you have sex during the last 12/uni00A0months?' even though how people interpret questions about having 'sex' can vary considerably based on age, gender, sexual identity, and the intersections of these (Byers et/uni00A0al., 2009; Hille et/uni00A0al., 2020; McBride et/uni00A0al., 2017; Sanders & Reinisch, 1999; Schick et/uni00A0al., 2016).

Other research has examined population-level sexual behavior trends by examining the proportion of the population reporting no partnered sex in a given year (termed

Wellings et/uni00A0al. (2019)-using three waves of data from the UK's National Surveys of Sexual Attitudes and Lifestyles (Natsal) completed in 1991, 2001, and 2012-found that frequency of sex among 16-44/uni00A0year olds had declined, more so among married participants and those in the 35-44 age group. The Natsal analysis used an item that asked about frequency of sex in the prior four weeks, clarifying to participants that 'this means vaginal intercourse, oral sex, anal sex.' In Germany, researchers compared data from two waves of a representative sample of women and men ages 18-99 and found that past-year sexual activity had declined from 2005 to 2016, though this was largely attributed to declining proportions of people cohabitating with a partner. In the German study, past-year sexual activity was measured with the item, 'Were you intimate with someone in the past 12/uni00A0months? Yes or no?' (Beutel et/uni00A0al., 2018; Burghardt et/uni00A0al., 2020). Further, small but significant declines in sexual frequency were described between the 2001/2002 and 2012/2013 waves of the Australia Studies of Health and Relationships (ASHR) among individuals ages 16-59, but so were expanded overall sexual repertoires (that is, more people reporting engaging in masturbation and sex toy use, among other non-coital sexual behaviors) (de Visser et/uni00A0al., 2014).



1 3

'sexually inactive' people). Using 1987-2015 data from 18- to 39-year-old adult participants in the National Fertility Survey of Japan, Ghaznavi et/uni00A0al. (2019) found increases in the proportion of young adults reporting never having had 'sexual intercourse with someone of the opposite sex' (the authors note that the term used in the surveyseikosho -is typically used to refer to vaginal intercourse). Ueda et/uni00A0al. (2020) used data from 10 rounds of the GSS to demonstrate increases in the proportions of 18-24-year-old US men reporting no partnered sex in the prior year as well as greater proportions of 25-34-year-old US women and men reporting no partnered sex in the prior year. Taken together, these studies from multiple countries demonstrate some level of decline in partnered sexual activities, at least among some age groups. Each of these studies has used population-based probability sampling (considered the gold standard in survey research; Catania et/uni00A0al., 2015), yet the measurement of sexual activity and/or frequency differs across studies and has at times been imprecise. Although these methodological and measurement differences hinder direct comparisons across countries, the consistency of findings supports a true secular decline in partnered sexual behaviors.

Sexual Repertoire

One aspect of sexual frequency that is understudied at the population level relates to a person's overall sexual repertoire. Assessing sexual repertoire expands understandings of how people have sex, beyond just engagement in 'sex,' 'intimacy,' or intercourse in the prior month or year. Studies in Australia (Richters et/uni00A0al., 2006), France (Messiah et/uni00A0al., 1995), and the USA (Herbenick et/uni00A0al., 2010b) have examined the composition of behaviors at sexual events for individuals and report that certain sexual behaviors are correlated within sexual events. As examples, oral sex and penile-vaginal intercourse (PVI) may be correlated (Herbenick et/uni00A0al., 2010b) as are giving and receiving oral sex (Messiah et/uni00A0al., 1995). The present research extends ideas about sexual repertoire by considering the diversity of people's sexual behaviors over the course of a year and to what extent such sexual behaviors may cluster among groups of people. Because the NSSHB is US nationally representative, spans a decade as of this writing, and includes a detailed assessment of past year sexual behaviors (e.g., solo and partnered masturbation, giving and receiving oral sex, PVI, anal intercourse), it is an ideal dataset to use to examine questions about potential changes in specific sexual behaviors over time.

Study Aims

Using data from participants in the 2009 and 2018 waves of the National Survey of Sexual Health and Behavior (NSSHB), separately for adolescents (14-17/uni00A0years) and

adults (18-49/uni00A0years), we aimed to: (1) assess changes in frequency of past-year PVI and (2) examine combinations of past-year sexual behaviors across the two waves. We hypothesized that we would observe lower frequency of PVI from 2009 to 2018. We also hypothesized that we would observe decreases in past-year PVI but increases in non-coital partnered behaviors (such as oral sex and anal sex) in 2018 as compared to 2009.

Method

Participants

The methods for the 2009 and 2018 NSSHB survey waves have been described in detail elsewhere (e.g., Fortenberry et/uni00A0al., 2010; Fu et/uni00A0al., 2019; Herbenick et/uni00A0al., 2010a; Reece et/uni00A0al., 2010). The NSSHB is a US nationally representative probability survey of adolescents and adults in the USA that was initiated in 2009, with six subsequent data collection waves occurring between 2012 and 2018 (Beckemeyer et/uni00A0al., 2019; Carter et/uni00A0al., 2019; Guerra-Reyes et/uni00A0al., 2018; Hensel et/uni00A0al., 2015; Herbenick et/uni00A0al., 2019a, 2019b).

All sampled adults received an invitational message from Ipsos with a link to an IRB-approved study information sheet. Those who consented to participate could then proceed to the online survey. Adolescents ages 14-17 were invited to participate only if their parent/guardian first consented to their invitation to participate. As incentives, KnowledgePanel® members who complete surveys can earn points to accumulate toward cash rewards or merchandise.

The NSSHB uses internet-based surveys administered by Ipsos (formerly GfK and Knowledge Networks) through their KnowledgePanel®. KnowledgePanel® members are recruited using address-based sampling via the US Postal Service's Delivery Sequence File, with recruitment occurring through an initial invitation letter, a reminder postcard, follow-up letter, and telephone calls when a matched landline telephone number is available. That is, KnowledgePanel® is established through probability-based sampling of US households and not through convenience methods (e.g., people cannot volunteer for the panel, and it is not an opt-in panel). Households without internet connection are provided with a web-enabled device and internet access upon enrollment. Further weighting adjustments, using the latest Current Population Survey (CPS) distribution as a benchmark, are then applied to account for minor differential attrition rates among recruited panel members. Ipsos then used a probability proportional to size procedure to identify a sampling frame for each wave of the NSSHB.

Once data collection was complete, Ipsos created poststratification weights to maximize generalizations to the US population. The post-stratification weights were generated

using an iterative proportional fitting (raking) procedure to ensure alignment with respect to all study benchmark distributions (gender, age, race/ethnicity, Census region, household income, home ownership status, metropolitan area, and internet access) based on the latest CPS.

Measures

Demographic and/uni00A0Other Key Variables

Demographic variables such as age, gender, race/ethnicity, marital status, annual household income, education, and adult employment status were collected as part of the research panel's recruitment and retention efforts. The 2009 and 2018 measures were identical.

Penile-Vaginal Intercourse Frequency

Participants were asked, 'Thinking about the past year, about how often have you engaged in penile-vaginal intercourse?' Response options included: not at all, a few times in the past year, once a month, a few times per month, once a week, 2-3 times per week, and almost every day. Similar to measures used in prior studies (Laumann et/uni00A0al., 1994; Twenge et/uni00A0al., 2017) frequency of PVI in the past year is reported using a score ranging from 0 (not at all) to 6 (almost every day).

Sexual Repertoire

Participants were asked, 'How recently have you…' (1) masturbated alone; (2) masturbated with a partner; (3) given oral sex to someone; (4) had someone give you oral sex; (5) had penile-vaginal intercourse; (6) had someone put their penis in your anus; or (7) (males only) put your penis in someone's anus. Response options were: done in the past 30/uni00A0days, done in the past 90/uni00A0days, done in the past 6/uni00A0months, done in the past year, done more than a year ago, and never done this.

Statistical Analysis

For Hypothesis 1-that we would observe a lower frequency of penile-vaginal intercourse from 2009 to 2018-linear regression was used to analyze the associations between survey year and PVI frequency. Similar to Twenge et/uni00A0al. (2017), we examined PVI frequency in two ways: (1) categorically from 0 to 6 (corresponding to the response options described above in Measures) and (2) with numerical estimates calculated by calculating an annual frequency based on the response categories (not at all = 0, a few times in the past year = 3, once a month = 12, a few times a month = 36,

2-3 times/week = 130, almost every day or every day = 365). For adults, the covariates were age, race/ethnicity, income, marital status, education, and employment. For adolescents, the model was adjusted for age and race/ethnicity.

To identify the latent subgroups engaging in similar patterns of behaviors in the population, Latent Class Analysis (LCA) was performed for both adolescents and adults in each of the 2009 and 2018 waves. LCA loadings are the conditional probability that someone in a particular class would have engaged in a certain sexual behavior at least once in the last year. The items with higher loadings for a specific class are considered to be part of that class. Afterwards, linear regressions were done to examine the associations between class, survey year and PVI frequency. All analyses were done using SAS for Windows 9.4 (SAS Institute, Cary, NC, USA).

For Hypothesis 2-that we would observe decreases in past-year PVI but increases in non-coital partnered sexual behaviors (such as oral sex and anal sex) in 2018 as compared to 2009-we did the following: First, sexual repertoire categories were dichotomized to participants that reported having engaged in a particular behavior 'more than a year ago or never' and 'at least once in the past year.' Having engaged in receptive or insertive anal sex was re-categorized as 'anal intercourse.' Descriptive statistics were calculated for sexual repertoire categories in each of the 2009 and 2018 waves. Then, separately for adults and adolescents, Chisquared tests were performed to examine whether there were different trends between the 2009 and 2018 waves for each sexual repertoire category (e.g., solo masturbation, partnered masturbation, etc.). Because they require different statistical weights in the dataset, all analyses were done separately for adults (18-49 year olds) and adolescents (14-17 year olds).

Results

Participants

A total of 1647 adolescents ages 14-17 and 7055 adults ages 18-49 were included from both waves of data. A total of 820 adolescents and 3335 adults (3070 weighted) were from the 2009 NSSHB, while 827 adolescents and 3720 adults (3719 weighted) were from the 2018 NSSHB. Additional demographic characteristics are shown in Table/uni00A01.

Past Year Frequency of/uni00A0Penile-Vaginal Intercourse

Hypothesis 1 was supported. Compared to adult participants in the 2009 NSSHB, those in the 2018 NSSHB were significantly more likely to report no PVI in the prior year (28% in 2018 vs. 24% in 2009). A similar difference in proportions



1 3

reporting no PVI was observed in the adolescent sample (89% in 2018 vs. 79% in 2009).

Among adolescents, those who reported no PVI in the prior year were significantly more likely to be 14-15 (compared to 16-17). As with adults, those who reported no PVI in the prior year were also significantly less likely to report having engaged in any of the other sexual behaviors we examined. There were no statistically significant differences in PVI frequency categories and adolescent gender, race/ethnicity, or household income.

Among adult participants, those who reported no PVI in the prior year were significantly more likely to be in the 18-2-year-old age category, Black/non-Hispanic, never married, have a lower household income (< $50,000/year), and less likely to have a college degree (Table/uni00A02). We also examined associations between past year PVI and other sexual behaviors. Additionally, those who reported no PVI in the prior year were also significantly less likely to report having engaged in any of the other sexual behaviors we examined.

Estimated Frequency of/uni00A0Past Year Penile-Vaginal Intercourse

After controlling for age and race/ethnicity, adolescents in the 2009 NSSHB were estimated to have PVI 14.37 times in the past year which was significantly more than the 4.32 PVI events estimated to occur among adolescents in the 2018 NSSHB (Table/uni00A03). Among adults ages 18-49, those in the 2009 had PVI an estimated 63.2 times which was significantly more times than adults in the 2018 NSSHB who had PVI an estimated 47.0 times. These differences remained significant after adjustment for age, race/ethnicity, income, marital status, and education.

Past Year Sexual Repertoire

Hypothesis 2 was partially supported; for both adolescents and adults, we observed decreases in reports of past year PVI. However, contrary to our hypothesis we did not observe increases in any of the non-coital partnered sexual behaviors assessed (i.e., partnered masturbation, giving oral sex, receiving oral sex, anal intercourse). In fact, all modes of partnered sex were reported less frequently in the past year in the 2018 NSSHB than in 2009.

Among 14-17-year-olds, significantly fewer 2018 NSSHB participants reported having engaged in every past year sexual behavior as compared to 2009 NSSHB participants-that is, in 2018 significantly fewer adolescents reported having engaged in solo masturbation, partnered masturbation, giving oral sex, receiving oral sex, PVI, and anal intercourse (Table/uni00A04).



Among 18-49/uni00A0year-old adults, significantly fewer 2018 NSSHB participants reported having engaged in every partnered sexual behavior assessed (partnered masturbation, gave oral, received oral, PVI, anal intercourse) as compared to the 2009 NSSHB participants (Table/uni00A04). However, there were no statistically significant differences in regard to participants' reports of prior year solo masturbation for 2009 versus 2018.

Latent Class Analyses: Sexual Repertoire

For latent class analyses, we selected four classes as additional classes were redundant (Table/uni00A05). Latent Class 1 was characterized by solo masturbation only for both adolescents and adults. Latent Class 2 was characterized by no sexual

behaviors at all for adolescents, and solo masturbation and PVI for adults. Latent Class 3 was characterized by engagement in all modes of sexual behavior. Latent Class 4 was characterized by inclusion of oral genital behaviors but exclusion of partnered masturbation and anal intercourse.

Overall, among adolescents we observed a significant change in participants' distribution across the classes from 2009 to 2018 (Fig./uni00A01). That is, membership in the Class 1 (solo masturbation), Class 3 (all sexual behaviors queried), and Class 4 decreased in frequency, whereas membership in the Class 2 (no sexual behaviors) increased in frequency from 2009 to 2018. When examining class distributions by gender, the same trend was observed for both adolescent women and adolescent men, with decreases in each of the



* p -values are for chi-square tests




three classes marked by solo and/or partnered sexual activities and increases in membership in Class 2 in 2018. Specifically, 28.8% of adolescent men ages 14-17 were categorized in Class 2 (no sexual behaviors) in 2009 compared to 44.2% in 2018. Among adolescent women, 49.5% were categorized in Class 2 in 2009 compared to 74.0% in 2018.

As can be seen in Table/uni00A06, in examining associations between survey year and class with PVI frequency categories, for adolescents there are significant differences by year, class, and the interaction between year and class. This means that classes have different trends in regard to their frequency of PVI. Class 1 adolescents (solo masturbation) increased their frequency of PVI in 2018, while the Class 2, 3, and 4 adolescents decreased their PVI frequency from 2009 to 2018. The decreases in PVI frequency for those categorized in Classes 3 and 4 were statistically significant.

For adults, the distribution of classes between 2009 and 2018 was significantly different, where Class 3 decreased its frequency, while the other classes increased their frequency from 2009 to 2018. When looking at these trends by gender, in Class 1 (solo masturbation only), men had a greater increase from 2009 to 2018 than did women, while for Class 4, women increased in membership 2018 and males decreased from 2009 to 2018.

For adults, there were also significant differences observed by year and by class. However, the interaction between year and class was not significant, as each of the four classes decreased in PVI frequency from 2009 to 2018 (unadjusted and adjusted). When looking at PVI frequency as an estimated number of times over the year, the trend is the same as when looking at it as categories.

Discussion

The present study used data from two waves of US nationally representative survey data to examine changes in sexual frequency and sexual repertoire between 2009 and 2018. Our research adds to the literature by using detailed measures of sexual behaviors beyond oral, vaginal, and anal intercourse; we did this in order to examine whether an explanation for declines in coital frequency might be explained by increases in non-coital behaviors. However, in addition to finding decreased PVI frequency in 2018 as compared to 2009, we found significant decreases across all partnered sexual behaviors assessed and, for adolescents, decreases in the proportion of adolescents reporting solo masturbation in the prior year as well. Overall, our findings are consistent with studies from multiple



countries that have documented declines in sexual frequency. Because our sample was limited to individuals ages 14-49, we were unable to examine sexual behavior trends among people aged 50 and older. However, our findings align with studies that have found greater proportions of young people reporting no partnered sexual behaviors in the prior year (e.g., Burghardt et/uni00A0al., 2020; Ghaznavi et/uni00A0al., 2019; Ueda & Mercer, 2019; Ueda et/uni00A0al., 2020).

Other than Natsal and ASHR, most population-representative studies examining sexual frequency trends have not included those under age 18 and thus less has been known at the population level about sexual trends among younger adolescents. Our study extends the literature by including adolescents as young as 14/uni00A0years old in our analytic sample (the youngest participants in Natsal and ASHR were 16/uni00A0years old). Findings from our research also align with the US Youth Risk Behavior Survey (YRBS) which has demonstrated declining rates of high school students reporting having ever had sex



1 3

over a similar period of time (e.g., 46% in 2009 vs. 38% in 2019) (Centers for Disease Control & Prevention, 2020a). The lower rates of adolescents' reports of solo masturbation and PVI in 2018 are striking and deserve further study. These differences aren't trivial: for example, the proportion of adolescents reporting neither solo nor partnered sexual behaviors (Latent Class 2) increased from 28.8% of young men and 49.5% of young women in 2009 to 43.3% of young men and 74.0% of young women in 2018.

A number of potentially convergent social and cultural changes may contribute to these substantial shifts in young people's sexual behaviors. Widespread internet connectivity and emerging new technologies have added a new medium for providing sexual experiences outside of physical sex with a partner (e.g., sexting, easy access to sexually explicit media) (Doring et/uni00A0al., 2017; Twenge et/uni00A0al., 2017; Wright, 2013; Wright et/uni00A0al., 2013). Alcohol use has decreased among adolescents (Miech et/uni00A0al., 2019), and many young people have been engaged in conversations about sexual consent



LCA loadings are the conditional probability that someone in a particular class would respond 'yes' (at least one in the last year) to a certain item. The items with higher loadings for a specific class are considered to be part of that Class. For example, the probability that someone in Class 1 indicated having engaged in solo masturbation is 0.561

In other words, 56% of the adults in Class 1 masturbated alone in the prior year Bolded entries reflect the sexual behaviors that characterize each class

(such as through the #MeToo movement led by Tarana Burke, the Obama/Biden administration's It's On Us campaign, and recent high profile rape cases) (e.g., Armstrong & Mahone, 2017; PettyJohn et/uni00A0al., 2019). Also, more contemporary young people identify with non-heterosexual identitiesincluding asexual identities-and more young people identify in gender expansive ways (Newport, 2018; Watson et/uni00A0al., 2020). It is also possible that secular trends reflect a tendency to have over-reported sexual behavior in earlier years, with more accurate reporting now as people become more comfortable with online presentations of themselves. These are among the many potential influences on adolescent sexual development and expression; subsequent research might examine how each of these may be contributing to changing patterns of sexual frequency and repertoire at the population level. Greater investment in understanding adolescent sexual development beyond risk is warranted, including how adolescents form, sustain, and interpret intimate relationships.

In terms of young adults, some research suggests that increasing use of computer games and social media may be implicated in young adults' declining sexual activity (Lei & South, 2021). A recent analysis of 18-23-year-olds in 2007-2017 waves of the Transition to Adulthood Supplement of the Panel Study of Income Dynamics found that increased use of computer games, decreased alcohol use, decreased earnings, and declines in romantic relationship formation explained 76% of the decline in sexually active young adults

in their sample (Lei & South, 2021). The median age at first marriage in the USA has also increased (US Census, 2020). It is worth noting that many published reports of adult sexual behavior (including ours) begin by describing the potential positive contributions of sex to health and quality of life. Media coverage of declining sexual activity tends to be similarly imbued with a sense that-in spite of risks that include unintended or mistimed pregnancy, sexually transmitted infections, and/or sad or lonely feelings connected to sexpartnered sex is generally pleasurable, joyful, connecting, and/or beneficial and thus declines in partnered sex among adults may be concerning (e.g., Feder, 2020; Julian, 2018). The age-old question on how much sex is too much and how little sex is not enough comes to mind. Given the impacts of the COVID-19 pandemic on physical and mental health, sexual behavior, relationships, and (for youth) in-person school and extracurricular activities, ongoing populationlevel research on sexual development and behaviors will be important (Finnerty et/uni00A0al., 2021; Rosenberg et/uni00A0al., 2021).

Positive aspects of adolescent partnered sex are less often highlighted. For example, in the section of the 2019 YRBS report that shows sexual behavior trends over time, the row that shows declining percentages of high school students who have 'ever had sex' also features a green symbol (similar to the US traffic light system) which the legend describes as moving 'in right direction' (Centers for Disease Control & Prevention, 2020b). The line between adolescence and

adulthood has always been tenuous-perhaps particularly so when it comes to sexual behavior-but we must continue to interrogate how declining adolescent sexual activity is in

the 'right direction' yet declining adult sexual activity warrants concern. Solo and partnered adolescent sexual exploration are developmentally normative, offer opportunities for



sis (adults, adolescents, adults by gender, adolescents by gender), class membership was significantly different from 2009 to 2018



learning and joy, and are supportive of adult sexual development (Hensel et/uni00A0al., 2011; Robbins et/uni00A0al., 2011; Tolman & McClelland, 2011). Our findings have implications for those in policy roles, who might consider other helpful metrics of understanding changes in adolescent sexual experience-as an example, tracking the proportion of adolescent sex that is wanted, consensual, and even pleasurable may be illuminating.

Findings from our study also extend the existing literature by including solo masturbation among participants' sexual behaviors. For both adults and adolescents, we found a latent class that was marked by engaging in solo masturbation. This highlights the important role of masturbation in people's sexual expression; however, we note that the proportion of adolescents in the solitary masturbation Latent Class 1 decreased in 2018 compared to 2009, while the proportion reporting

neither solo nor partnered sex increased. The 2009/2019 NSSHB waves did not ask participants how they feel about their sexual lives or whether they would like to have more sex or less sex than they are having; however, we note that Ueda and Mercer (2019) found that most Natsal participants who reported no prior year partnered sex but who did have prior partnered sexual experience were not dissatisfied with their sexual lives. Subsequent research should include more questions about people's own subjective assessments of their sexual lives and feelings about their solo and partnered sexual behaviors.

Recent research suggests that some sexual behaviors sometimes described as aggressive or as 'rough sex' may have grown in prevalence in the USA, including choking during sex (which is technically a form of strangulation) (Herbenick et/uni00A0al., 2020; Herbenick et/uni00A0al., 2021a). Like anal sex behaviors, choking/strangulation is often wanted, asked for, and/or perceived as pleasurable (Herbenick et/uni00A0al., 2021a, 2021b). However, being choked/strangled has also been identified by many women as an example of something a partner has done during sex that made them feel scared (Herbenick et/uni00A0al., 2019a, 2019b), which is not surprising given that choking/strangulation is a common feature of sexual assault, intimate partner violence, and (in rare cases) is lethal even as part of consensual sex (e.g., Mcquown et/uni00A0al., 2016; Roma et/uni00A0al., 2013; Sendler, 2018). Subsequent research might examine the extent to which partnered sex may be declining, at least for some subset of the population, as a result of experiencing unpleasant or frightening experiences during otherwise consensual sex (e.g., being hit, punched, slapped, or choked without consent, or as a form of sexual compliance).

Similarly, we need to understand more about how people's subjective feelings about the sex they've experienced may shape their subsequent choices about sex. At the population level, the 2009 NSSHB demonstrated that anal intercourse had nearly doubled in lifetime prevalence since the National Health and Social Life Survey of the early 1990s. However, anal sex remained infrequent overall in any given year (though much more frequent among gay and bisexual men) (Dodge et/uni00A0al., 2016; Herbenick et/uni00A0al., 2010a). Anal sex has generally been rated as unappealing among US adults (Herbenick et/uni00A0al., 2017), and several qualitative studies examining anal intercourse between women and men found thatalthough anal sex behaviors were pleasurable to some-anal sex was often marked by pressure, coercion, lack of communication, fear, and pain among women (e.g., Fahs & Gonzalez, 2014; Fahs et/uni00A0al., 2015; Herbenick et/uni00A0al., 2015, 2019a, 2019b; Jozkowski et/uni00A0al., 2014). Given these experiences, it is perhaps not surprising to have observed a decrease in anal intercourse between the 2009 and 2018 NSSHB, but that does not explain other decreases across all partnered sexual behaviors queried.



Strengths and/uni00A0Limitations

Our study was subject to several strengths and limitations. Among our strengths, we used data from the 2009 and 2018 waves of the NSSHB, a US nationally representative probability survey. The NSSHB is unique in that it includes items related to both sexual frequency and repertoire as well as a detailed assessment of solo and partnered sexual behaviors, which allowed for an examination of specific behavioral trends over two time periods. Other US national surveys, such as the GSS, YRBS, National Survey of Family Growth, and the National Longitudinal Study of Adolescent to Adult Health, are more limited in the scope of sexual behavior items assessed (Centers for Disease Control & Prevention, 2020a, 2020b; Harris et/uni00A0al., 2009; NORC at the University of Chicago, 2016). Both the 2009 and 2018 NSSHB waves were conducted through online, confidential surveys which has been shown to facilitate the reporting of sensitive behaviors. Among our limitations is that-in terms of frequency of sex-we were limited to comparisons of PVI (i.e., frequency of other sexual behaviors had not been assessed in both waves). Also, neither wave included an oversample of individuals who identify as lesbian, gay, bisexual, or asexual and thus-being a general population survey-findings largely reflect majority groups (e.g., heterosexual identified people). This becomes particularly apparent in examining the LCA classes, for which PVI loaded heavily on three of the four adult classes and two of the four adolescent classes. This is likely a fair representation of sex between males and females, given prior research showing the prevalence of PVI in many combinations of sex between women and men, and other research describing the intercourse imperative (Herbenick et/uni00A0al., 2010b; Richters et/uni00A0al., 2006). However, it does mean that these LCA classes do not reflect the rich diversity of all US adolescents and adults. Subsequent research might investigate similar constellations of intimate and/or sexual behaviors among dedicated samples of LGBTQ + individuals and/or among general population samples with sufficiently sized oversamples of LGBTQ + individuals.

Similarly, although the 2009/2018 NSSHB waves included a broad range of sexual behaviors for comparison, we would have liked to have been able to compare additional behaviors across waves but did not have additional items common among the two waves (e.g., kissing, cuddling, sex toy use, sexting, reading erotica, and/or watching pornography). As the NSSHB is focused on sexuality, we also did not have measures of more general behaviors (e.g., media use, substance use, mental health, physical health, perceived racism, political stress, etc.) that could have shed light on potential changes in sexual behaviors from 2009 to 2018. Finally, although our findings may help clinicians contextualize questions or concerns their clients have about how often people have sex, it is left to the client-clinician relationship, and

to people themselves, to examine contexts of pleasure and satisfaction.

Conclusions

The present study found a decrease in PVI frequency between the 2009 and 2018 NSSHB waves; we also found significant differences in past year sexual repertoire for both adults and adolescents, including decreases in partnered masturbation, giving and receiving oral sex, PVI, and anal intercourse. Additionally, we observed a significant decrease in the proportion of adolescents reporting solo masturbation in the prior year between 2009 and 2018. These findings have implications for sexual health researchers, clinicians, and educators.

Supplementary Information The online version contains supplementary material available at https:// doi. org/ 10. 1007/ s10508- 021- 02125-2.

Acknowledgements The present analyses were funded through support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) (R03HD101726-01; MPIs Herbenick and Fu). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We are grateful to Stephanie Dickinson for her contributions in support of data analysis and interpretation. The 2009 and 2018 NSSHB were supported by grants from Church and Dwight Co., Inc., maker of Trojan brand sexual health products (2009 Co-PIs: Reece and Herbenick; 2018 PI: Herbenick). We wish to acknowledge the valuable contributions of Jonathon Beckmeyer, Brian Dodge, Devon Hensel, Michael Reece, and Stephanie Sanders in the development of the 2009 and/or 2018 waves of the National Survey of Sexual Health and Behavior.

Authors' Contributions Herbenick and Fortenberry contributed to the development of the 2009 NSSHB survey; Herbenick and Fu contributed to the development of the 2018 NSSHB survey. Rosenberg and GolzarriArroyo analyzed the data. All authors contributed to manuscript preparation, review, and approval.

Funding The present analyses were funded through support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) (R03HD101726-01; MPIs Herbenick and Fu). The 2009 and 2018 NSSHB were originally supported by grants from Church and Dwight Co., Inc., maker of Trojan brand sexual health products.

Declarations

Ethical approval The Institutional Review Board at Indiana University reviewed and approved study protocols and questionnaires used in the NSSHB (Protocols 0,812,000,042, 1,408,833,205, and 1,906,506,253).

Conflict of interest Authors declare that they have no conflict of interest.

Data Availability If accepted for publication, a limited data set may be archived at Indiana University.

References

Armstrong, C. L., & Mahone, J. (2017). 'It's on us'. The role of social media and rape culture in individual willingness to mobilize against sexual assault. Mass Communication and Society, 20 , 92-115.

• Beutel, M. E., Burghardt, J., Tibubos, A. N., Klein, E. M., Schmutzer, G., & Brähler, E. (2018). Declining sexual activity and desire in men-Findings from representative German surveys, 2005 and 2016. Journal of Sexual Medicine, 15 , 750-756.
• Beckmeyer, J. J., Herbenick, D., Fu, T., Dodge, B., Reece, M., & Fortenberry, J. D. (2019). Characteristics of adolescent sexting: Results from the 2015 National Survey of Sexual Health and Behavior. Journal of Sex & Marital Therapy, 45 , 767-780.
• Burghardt, J., Beutel, M. E., Hasenburg, A., Schmutzer, G., & Brähler, E. (2020). Declining sexual activity and desire in women: Findings from representative German surveys 2005 and 2016. Archives of Sexual Behavior, 49 , 919-925.
• Carter, A., Ford, J. V., Luetke, M., Fu, T. J., Townes, A., Hensel, D. J., Dodge, B., & Herbenick, D. (2019). 'Fulfilling his needs, not mine': Reasons for not talking about painful sex and associations with lack of pleasure in a nationally representative sample of women in the United States. Journal of Sexual Medicine, 16 , 1953-1965.
• Byers, E. S., Henderson, J., & Hobson, K. M. (2009). University students' definitions of sexual abstinence and having sex. Archives of Sexual Behavior, 38 , 665-674.
• Catania, J. A., Dolcini, M. M., Orellana, R., & Narayanan, V. (2015). Nonprobability and probability-based sampling strategies in sexual science. Journal of Sex Research, 52 , 396-411.

Centers for Disease Control and Prevention (2020b). Youth Risk Behavior Survey: Data Summary & Trends Report 2009-2019 . Retrieved from https:// www. cdc. gov/ healt hyyou th/ data/ yrbs/ yrbs_ data_ summa ry_ and_ trends. htm

• Centers for Disease Control and Prevention. (2020a). National Survey of Family Growth: Questionnaires, datasets, and related documentation . Retrieved from https:// www. cdc. gov/ nchs/ nsfg/ nsfg_ quest ionna ires. htm
• de Visser, R. O., Richters, J., Rissel, C., Badcock, P. B., Simpson, J. M., Smith, A. M., & Grulich, A. E. (2014). Change and stasis in sexual health and relationships: Comparisons between the first and second Australian Studies of Health and Relationships. Sexual Health, 11 , 505-509.

Döring, N., Daneback, K., Shaughnessy, K., Grov, C., & Byers, E. S. (2017). Online sexual activity experiences among college students: A four-country comparison. Archives of Sexual Behavior, 46 , 1641-1652.

Dodge, B., Herbenick, D., Fu, T., Schick, V., Reece, M., Sanders, S., & Fortenberry, J. D. (2016). Sexual behaviors of US men by self-identified sexual orientation: Results from the 2012 National Survey of Sexual Health and Behavior. Journal of Sexual Medicine, 13 , 637-649.

Fahs, B., & Gonzalez, J. (2014). The front lines of the 'back door': Navigating (dis)engagement, coercion, and pleasure in women's anal sex experiences. Feminism & Psychology, 24 , 500-520.

Feder, S. (2020, June 12). Americans are having less sex than ever, and experts say the pandemic will only fuel this downward spiral. Insider.com . Retrieved from https:// www. insid er. com/

Fahs, B., Swank, E., & Clevenger, L. (2015). Troubling anal sex: Gender, power, and sexual compliance in heterosexual experiences of anal intercourse. Gender Issues, 32 , 19-38.

Field, N., Mercer, C. H., Sonnenberg, P., Tanton, C., Clifton, S., Mitchell, K. R., Erens, B., Macdowall, W., Wu, F., Datta, J., Jones, K. G., Stevens, A., Prah, P., Copas, A. J., Phelps, A., Wellings, K., & Johnson, A. M. (2013). Associations between


Finnerty, R., Marshall, S. A., Imbault, C., & Trainor, L. J. (2021). Extra-curricular activities and well-being: Results from a survey of undergraduate university students during COVID-19 lockdown restrictions. Frontiers in Psychology, 12 , 2316. https:// doi. org/ 10. 3389/ fpsyg. 2021. 647402

health and sexual lifestyles in Britain: Findings from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). Lancet, 382 , 1830-1844.

• Fortenberry, J. D., Schick, V., Herbenick, D., Sanders, S. A., Dodge, B., & Reece, M. (2010). Sexual behaviors and condom use at last vaginal intercourse: A national sample of adolescents ages 14 to 17 years. Journal of Sexual Medicine, 7 , 305-314.
• Ghaznavi, C., Sakamoto, H., Yoneoka, D., Nomura, S., Shibuya, K., & Ueda, P. (2019). Trends in heterosexual inexperience among young adults in Japan: Analysis of national surveys, 19872015. BMC Public Health, 19 , 355. https:// doi. org/ 10. 1186/ s12889- 019- 6677-5
• Fu, T., Hensel, D. J., Beckmeyer, J. J., Dodge, B., & Herbenick, D. (2019). Considerations in the measurement and reporting of withdrawal: Findings from the 2018 National Survey of Sexual Health and Behavior. Journal of Sexual Medicine, 16 , 1170-1177.
• Guerra-Reyes, L., Fu, T., Williams, D., Herbenick, D., Dodge, B., Reece, M., & Fortenberry, J. D. (2018). Knowledge of Zika and perception of risk among sexually-active adults in the United States of America: Results from a nationally representative sample. Revista Panamericana De Salud Publica, 42 , e43. https:// doi. org/ 10. 26633/ RPSP. 2018. 43
• Hensel, D. J., Fortenberry, J. D., O'Sullivan, L. F., & Orr, D. P. (2011). The developmental association of sexual self-concept with sexual behavior among adolescent women. Journal of Adolescence, 34 , 675-684.
• Harris, K. M., Halpern, C. T., Whitsel, E., Hussey, J., Tabor, J., Entzel, P., & Udry, J.R. (2009). The National Longitudinal Study of Adolescent to Adult Health: Research design . Retrieved from https:// addhe alth. cpc. unc. edu/ docum entat ion/ study- design/
• Hensel, D. J., Schick, V., Herbenick, D., Dodge, B., Reece, M., Sanders, S. A., & Fortenberry, J. D. (2015). Lifetime lubricant use among a nationally representative sample of lesbian- and bisexual-identified women in the United States. Journal of Sexual Medicine, 12 , 1257-1266. https:// doi. org/ 10. 1111/ jsm. 12873

Herbenick, D., Bartelt, E., Fu, T. C., Paul, B., Gradus, R., Bauer, J., & Jones, R. (2019a). Feeling scared during sex: Findings from a US probability sample of women and men ages 14 to 60. Journal of Sex & Marital Therapy, 45 , 424-439.

Herbenick, D., Fu, T., Svetina Valdivia, D., Patterson, C., Rosenstock Gonzalez, Y., Guerra-Reyes, L., Eastman-Mueller, H., Beckmeyer, J., & Rosenberg, M. (2021). What is rough sex, who does it, and who likes it? Findings from a probability survey of U.S. undergraduate students. Archives of Sexual Behavior, 50 , 1183-1195.

• Herbenick, D., Bowling, J., Fu, T. C., Dodge, B., Guerra-Reyes, L., & Sanders, S. (2017). Sexual diversity in the United States: Results from a nationally representative probability sample of adult women and men. PLoS ONE, 12 , e0181198. https:// doi. org/ 10. 1371/ journ al. pone. 01811 98
• Herbenick, D., Fu, T. C., Wright, P., Paul, B., Gradus, R., Bauer, J., & Jones, R. (2020). Diverse sexual behaviors and pornography use: Findings from a nationally representative probability survey of Americans aged 18 to 60 years. Journal of Sexual Medicine, 17 , 623-633.
• Herbenick, D., Fu, T. C., Owens, C., Bartelt, E., Dodge, B., Reece, M., & Fortenberry, J. D. (2019b). Kissing, cuddling, and massage at most recent sexual event: Findings from a U.S. nationally representative probability sample. Journal of Sex & Marital Therapy, 48 , 159-172. https:// doi. org/ 10. 1080/ 00926 23X. 2018. 14946 48

• Herbenick, D., Patterson, C., Beckmeyer, J., Rosenstock Gonzalez, Y. R., Luetke, M., Guerra-Reyes, L., Eastman-Mueller, H., Svetina Valdivia, D., & Rosenberg, M. (2021b). Diverse sexual behaviors in undergraduate students: Findings from a campus probability survey. Journal of Sexual Medicine., 18 (6), 1024-1041.
• Herbenick, D., Reece, M., Schick, V., Sanders, S. A., Dodge, B., & Fortenberry, J. D. (2010b). An event-level analysis of the sexual characteristics and composition among adults ages 18 to 59: Results from a national probability sample in the United States. Journal of Sexual Medicine, 7 , 346-361.
• Herbenick, D., Reece, M., Schick, V., Sanders, S. A., Dodge, B., & Fortenberry, J. D. (2010a). Sexual behavior in the United States: Results from a national probability sample of men and women ages 14-94. Journal of Sexual Medicine, 7 , 255-265.
• Herbenick, D., Schick, V., Sanders, S. A., Reece, M., & Fortenberry, J. D. (2015). Pain experienced during vaginal and anal intercourse with other-sex partners: Findings from a nationally representative probability study in the United States. Journal of Sexual Medicine, 12 , 1040-1051.
• Hille, J. J., Simmons, M. K., & Sanders, S. A. (2020). 'Sex' and the ace spectrum: Definitions of sex, behavioral histories, and future interest for individuals who identify as asexual, graysexual, or demisexual. Journal of Sex Research, 57 , 813-823.
• Hess, R., Conroy, M. B., Ness, R., Bryce, C. L., Dillon, S., Chang, C. C. H., & Matthews, K. A. (2009). Association of lifestyle and relationship factors with sexual functioning of women during midlife. Journal of Sexual Medicine, 6 , 1358-1368.
• Jozkowski, K. N., Peterson, Z. D., Sanders, S. A., Dennis, B., & Reece, M. (2014). Gender differences in heterosexual college students' conceptualizations and indicators of sexual consent: Implications for contemporary sexual assault prevention education. Journal of Sex Research, 51 , 904-916.

Kaestle, C. E., & Allen, K. R. (2011). The role of masturbation in healthy sexual development: Perceptions of young adults. Archives of Sexual Behavior, 40 , 983-994.

Julian, K. (2018, December). Why are young people having so little sex? Atlantic . Retrieved from: https:// www. theat lantic. com/

• Laumann, E. O., Gagnon, J. H., Michael, R. T., & Michaels, S. (1994). The social organization of sexuality: Sexual practices in the United States . University of Chicago Press.
• Levin, R. J. (2007). Sexual activity, health and well-being-the beneficial roles of coitus and masturbation. Sexual and Relationship Therapy, 22 , 135-148.
• Lei, L., & South, S. J. (2021). Explaining the decline in young adult sexual activity in the United States. Journal of Marriage and Family, 83 , 280-295.
• Lindau, S. T., & Gavrilova, N. (2010). Sex, health, and years of sexually active life gained due to good health: Evidence from two US population based cross sectional surveys of ageing. British Medical Journal, 340 , c810. https:// doi. org/ 10. 1136/ bmj. c810

McBride, K. R., Sanders, S. A., Hill, B. J., & Reinisch, J. M. (2017). Heterosexual women's and men's labeling of anal behaviors as having 'had sex.' Journal of Sex Research, 54 , 1166-1170.

Lindau, S. T., Schumm, L. P., Laumann, E. O., Levinson, W., O'Muircheartaigh, C. A., & Waite, L. J. (2007). A study of sexuality and health among older adults in the United States. New England Journal of Medicine, 357 , 762-774.

• McNulty, J. K., Wenner, C. A., & Fisher, T. D. (2016). Longitudinal associations among relationship satisfaction, sexual satisfaction, and frequency of sex in early marriage. Archives of Sexual Behavior, 45 , 85-97.
• Mcquown, C., Frey, J., Steer, S., Fletcher, G. E., Kinkopf, B., Fakler, M., & Prulhiere, V. (2016). Prevalence of strangulation in survivors of sexual assault and domestic violence. American Journal of Emergency Medicine, 34 (7), 1281-1285.
Messiah, A., Blin, P., & Fiche, V. (1995). Sexual repertoires of heterosexuals: Implications for HIV/sexually transmitted disease risk and prevention. AIDS, 9 , 1357-1366.

• Mitchell, K. R., Mercer, C. H., Ploubidis, G. B., Jones, K. G., Datta, J., Field, N., & Wellings, K. (2013). Sexual function in Britain: Findings from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). Lancet, 382 , 1817-1829. https:// doi. org/ 10. 1016/ s0140- 6736(13) 62366-1

Miech, R. A., Johnston, L. D., O'Malley, P. M., Bachman, J. G., Schulenberg, J. E., & Patrick, M. E. (2019). Monitoring the future national survey results on drug use, 1975-2018: Volume I, Secondary school students . Ann Arbor: Institute for Social Research, The University of Michigan. Retrieved from http:// monit oring thefu ture. org/ pubs. html# monog raphs

Newport, F. (2018, May 22). In U.S., estimate of LGBT population rises to 4.5%. Gallup. Retrieved from https:// news. gallup. com/

PettyJohn, M. E., Muzzey, F. K., Maas, M. K., & McCauley, H. L. (2019). #HowIWillChange: Engaging men and boys in the #MeToo movement. Psychology of Men & Masculinities, 20 , 612-622.

NORC at the University of Chicago. (2016). The General Social Survey . Retrieved from https:// gss. norc. org/

Reece, M., Herbenick, D., Schick, V., Sanders, S. A., Dodge, B., & Fortenberry, J. D. (2010). Background and considerations on the National Survey of Sexual Health and Behavior (NSSHB) from the investigators. Journal of Sexual Medicine, 7 , 243-245.

Robbins, C. L., Schick, V., Reece, M., Herbenick, D., Sanders, S. A., Dodge, B., & Fortenberry, J. D. (2011). Prevalence, frequency, and associations of masturbation with partnered sexual behaviors among U.S. adolescents. Archives of Pediatrics & Adolescent Medicine, 165 , 1087-1093.

Richters, J., de Visser, R., Rissel, C., & Smith, A. (2006). Sexual practices at last heterosexual encounter and occurrence of orgasm in a national survey. Journal of Sex Research, 43 , 217-226.

Roma, P., Pazzelli, F., Pompili, M., Girardi, P., & Ferracuti, S. (2013). Shibari: Double hanging during consensual sexual asphyxia. Archives of Sexual Behavior, 42 (5), 895-900.

Sanders, S. A., & Reinisch, J. M. (1999). Would you say you had sex if...? Journal of the American Medical Association, 281 , 275-277. Schick, V. R., Rosenberger, J. G., Herbenick, D., Collazo, E., Sanders, S. A., & Reece, M. (2016). The behavioral definitions of 'having sex with a man' and 'having sex with a woman' identified by women who have engaged in sexual activity with both men and women. Journal of Sex Research, 53 , 578-587.

Rosenberg, M., Luetke, M., Hensel, D., Kianersi, S., Fu, T. C., & Herbenick, D. (2021). Depression and loneliness during April 2020 COVID-19 restrictions in the United States, and their associations with frequency of social and sexual connections./uni00A0 Social Psychiatry and Psychiatric Epidemiology, 56 , 1221-1232.

• Schmiedeberg, C., Huyer-May, B., Castiglioni, L., & Johnson, M. D. (2017). The more or the better? How sex contributes to life satisfaction. Archives of Sexual Behavior, 46 , 465-473.
• Sprott, R. A., & Benoit Hadcock, B. (2018). Bisexuality, pansexuality, queer identity, and kink identity. Sexual and Relationship Therapy, 33 , 214-232.
• Sendler, D. J. (2018). Lethal asphyxiation due to sadomasochistic sex training-How some sex partners avoid criminal responsibility even though their actions lead to someone's death. Journal of Forensic and Legal Medicine, 56 , 59-65.
• Tolman, D. L., & McClelland, S. I. (2011). Normative sexuality development in adolescence: A decade in review, 2000-2009. Journal of Research on Adolescence, 21 , 242-255.
• Ueda, P., & Mercer, C. H. (2019). Prevalence and types of sexual inactivity in Britain: Analyses of national cross-sectional probability survey data. British Medical Journal Open, 9 , e030708. https:// doi. org/ 10. 1136/ bmjop en- 2019- 030708
• Twenge, J. M., Sherman, R. A., & Wells, B. E. (2017). Declines in sexual frequency among American adults, 1989-2014. Archives of Sexual Behavior, 46 , 2389-2401.
• Ueda, P., Mercer, C. H., Ghaznavi, C., & Herbenick, D. (2020). Trends in frequency of sexual activity and number of sexual partners among adults aged 18 to 44 years in the US, 2000-2018. JAMA Network Open, 3 (6), e203833-e203833.
• Watson, R. J., Wheldon, C. W., & Puhl, R. M. (2020). Evidence of diverse identities in a large national sample of sexual and gender minority adolescents. Journal of Research on Adolescence, 30 , 431-442.
• U.S. Census. (2020). Historical marital status tables . Retrieved on July 29, 2021 from: https:// www. census. gov/ data/ tables/ timeseries/ demo/ famil ies/ marit al. html
• Wellings, K., Palmer, M. J., Machiyama, K., & Slaymaker, E. (2019). Changes in, and factors associated with, frequency of sex in Britain: Evidence from three National Surveys of Sexual Attitudes and Lifestyles (Natsal)./uni00A0 BMJ ,/uni00A0 365 . https:// doi. org/ 10. 1136/ bmj. l1525

Wright, P. J. (2013). US males and pornography, 1973-2010: Consumption, predictors, correlates. Journal of Sex Research, 50 , 60-71.

World Health Organization. (2006)./uni00A0 Defining sexual health: Report of a Technical Consultation on Sexual Health, 28-31 January 2002, Geneva .

Wright, P. J., Bae, S., & Funk, M. (2013). United States women and pornography through four decades: Exposure, attitudes, behaviors, individual differences. Archives of Sexual Behavior, 42 , 1131-1144.

Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.