Trends in Frequency of Sexual Activity and Number of Sexual Partners Among Adults Aged 18 to 44 Years in the US, 2000-2018

This survey study of adults aged 18 to 44 years examines trends in reported frequency of sexual activity and number of sexual partners and the association between measures of sexual activity and sociodemographic variables.


Introduction
Sexual health and satisfaction are key components of health and well-being. [1][2][3] Sexual relationships can positively influence life satisfaction and happiness, [4][5][6] and sexual activity may lower heart rate and blood pressure 7,8 while also reducing stress by promoting oxytocin release. 9 Conversely, lower sexual activity has been associated with increased mortality 10 and poor self-reported health, 11 although these associations warrant careful interpretation because sexual activity and health outcomes may have common causes and healthier individuals may have more sexual activity.
Although sexual inactivity and sexual frequency have recently been subject to increased scrutiny from public health perspectives, [11][12][13][14] uncertainty remains regarding recent trends in sexual activity among US adults. A study 15 using nationally representative data from the General Social Survey  found that at 20 to 24 years of age, 6.3% of Americans born in 1965 to 1969 reported having had no sexual partners after 18 years of age. This proportion was 11.5% for those born in 1970 to 1979, 11.7% for those born in 1980 to 1989, and 15.2% for those born in 1990 to 1994.
Although this study 15 found that sexual inactivity in one's early 20s was less common among those born in 1965 to 1969 than in subsequent generations, to our knowledge, trends in sexual inactivity and in regular sexual frequency have not been assessed using a wider range of age and sex groups and more recent data. Another study 16 using data from the same survey estimated that US adults (aged Ն18 years) had sexual frequencies of approximately 9 fewer times per year in the early 2010s compared with the late 1990s. Because these analyses did not account for the distribution of sexual activity in the population, it is unclear whether this finding was attributable to a decreased sexual frequency among sexually active adults or whether it represented an increase in the proportion who did not have sexual activity at all. This distinction is important because the societal and public health implications of the 2 potential mechanisms differ substantially.
Using data from 18-to 44-year-old participants in the General Social Survey from 2000 to 2018, we assessed trends in categories of sexual frequency (including sexual inactivity) and number of sexual partners in the year preceding survey participation. We then examined factors associated with sexual frequency and the number of sexual partners.

Study Population
The General Social Survey is a nationally representative, biennial survey of US adults 18 years or older (eAppendix in the Supplement). 17 We used data from 10 waves of the survey in 2000 to 2018. We included all participants aged 18 to 44 years who had been asked the questions regarding sexual frequency and number of sexual partners in the past year, as described below (eAppendix and eTable 1 in the Supplement). For analyses on sexual frequency, we excluded 381 individuals with unknown sexual frequency (weighted, 3.9%), and for analyses on number of sexual partners, we excluded 136 with unknown number of partners (weighted, 1.3%) (eTable 2 in the Supplement). The General Social Survey was approved by the institutional review board at the National Opinion Research Center, University of Chicago. Participants provided oral informed consent for interviews.
All data were deidentified. The survey is conducted by the National Opinion Research Center at the

Measures of Sexual Activity
We assessed 2 measures of sexual activity in the past year: sexual frequency and number of sexual partners. The survey included the question, "About how often did you have sex during the last 12 months?" with response options ranging from "not at all" to "more than 3 times a week" (eAppendix in the Supplement). We categorized sexual frequency in the past year into (1) sexually inactive (no sex during the past year), (2) once or twice per year, (3) 1 to 3 times per month, and (4) weekly or more. The question, "How many sex partners have you had in the last 12 months?" could be answered with choices ranging from "no partners" to "more than 100 partners" (eAppendix in the Supplement).
We categorized number of sexual partners in the past year into (1) no partners, (2) 1 partner, (3) 2 partners, and (4) 3 or more partners. The rationale for the categories used is provided in the eAppendix in the Supplement.

Statistical Analysis
Analyses were performed in Stata, version 15.0 (StataCorp) and accounted for the stratification, clustering, and weighting of the samples. Analyses were performed separately by sex because of differences in the experience and reporting of sexual behaviors 18 and the meaning and interpretation that shape these behaviors. 19 First, we used the 2016-2018 survey to assess the proportion of the population in each category of sexual frequency and number of sexual partners in the total age range and by age group (18-24, 25-34, and 35-44 years, as in previous studies 12,13,18 ), using the χ 2 test to assess differences in proportions between sexes. Second, we estimated these proportions in all surveys, grouped pairwise to increase statistical power (2000-2002, 2004-2006, 2008-2010, 2012-2014, and 2016-2018), in the total age range, by age group, and by marital status. All reported percentages are weighted. We applied logistic regression to assess trends over time for each category of sexual frequency and number of sexual partners by calculating age-adjusted odds ratios (aORs) using the investigated category of sexual frequency or number of partners as the dependent variable and age and survey period (survey pairs as described above) as independent variables.
We assessed the association between sociodemographic and behavioral variables and sexual inactivity, weekly sex or more, no sexual partners, and Ն3 sexual partners in the past year. We focused on these measures of sexual activity because they constitute the extremes of the categories used in our analyses and have been used in previous studies. 12,14,20 We calculated aORs using the investigated measure of sexual activity as the dependent variable and age, survey period, and the variable of interest as the independent variables. Definitions of and the rationale for analyzing the sociodemographic and behavioral variables are given in eTable 3 in the Supplement.
Because the pairwise grouping of surveys may have obscured trends in the investigated measures of sexual activity, we performed additional analyses in which we analyzed each survey year separately. Because we found statistically significant trends in sexual inactivity, weekly or more sexual activity, and having no sexual partner among men, we performed post hoc analyses in which we assessed these trends in sociodemographic subgroups of men. To examine whether changes in the distribution of sociodemographic characteristics could explain the observed trends, we also assessed the trends using multivariable logistic regression models adjusted for the sociodemographic variables that were available during the entire study period (eTable 3 in the Supplement). Finally, we assessed the distribution of sexual frequency and number of sexual partners among participants identifying as gay, lesbian, or bisexual.

Women Men
Error bars represent 95% CIs. The total age range is shown in eFigure 1 in the Supplement.

Trends in Sexual Frequency and Number of Sexual Partners
In the total age range, sexual inactivity among men increased from 9.  Among women, the distribution of sexual activity in the total age range remained stable during the study period ( Figure 2 and Figure 4 and eFigure 2, eTable 8, and eTable 9 in the Supplement).
When analyzed by age group, sexual inactivity increased among women aged 25 to 34 ( the Supplement). Decrease in weekly or more sexual activity occurred among both unmarried and married men, with the decrease among married men coinciding with an increase in a sexual frequency of 1 to 3 times per month. Although sexual activity was largely unchanged among unmarried women, a decrease in weekly or more sexual activity and an increase in a sexual frequency of 1 to 3 times per month were observed among married women (eFigure 3, eTable 10, and eTable 11 in the Supplement).

Factors Associated With Sexual Activity
Associations of sexual inactivity with sociodemographic and behavioral variables are given in the  Error bars represent 95% CIs. Supplement. Black men (vs white men) and men and women identifying as gay, lesbian, or bisexual (vs heterosexual) were more likely to report 3 or more sexual partners. Use of pornographic material was associated with a lower likelihood of sexual inactivity among both men and women.  Error bars represent 95% CIs. In multivariable logistic regression models adjusted for sociodemographic variables, including changes in the proportion married, the aORs for the trend remained largely similar to those in the primary analyses for sexual inactivity, no sexual partners, and weekly or more sexual activity among men (eTable 18 in the Supplement). The distribution of sexual frequency and number of sexual partners among participants identifying as gay, lesbian, or bisexual is shown in eFigure 6 in the Supplement.

Discussion
Using US nationally representative survey data, we estimated that 30.9% of men and 19.  Error bars represent 95% CIs.  to 24 years and among men and women aged 25 to 34 years. The increase in sexual inactivity coincided with decreases in the proportion reporting sexual activity at least weekly or 1 sexual partner and occurred mainly among unmarried men. Among married men and women, there was a decrease in sexual activity at least weekly, whereas sexual inactivity was rare and did not change substantially. Men with lower income and with part-time or no employment were more likely to be sexually inactive, as were men and women who were students.  12 Although our analyses found an increase in sexual inactivity among unmarried men, these previous studies 12,16,21,22 did not find decreases in the mean sexual frequency among unpartnered individuals. Although this apparent discrepancy can be explained by our use of more recent data and differences in the studied populations and age and sex groups, it is also possible that changes in the distribution of sexual frequency might have gone   unnoticed in analyses of mean sexual frequency. Of importance, although the mean sexual frequency among those who were sexually active may reflect their priorities and preferences, sexual inactivity may reflect an absence of sexually intimate relationships, with substantially different implications for public health and society. As such, our study highlights the importance of assessing the distribution of sexual activity in populations rather than just the mean frequency, especially given the increasing number of unpartnered individuals.

JAMA Network Open | Public Health
Several hypotheses for why individuals engage in less sexual activity have been proposed.
Although theories regarding the use of pornography and longer working hours were not supported by our analyses, plausible reasons include changes in sexual norms that may affect actual and reported sexual activity; the stress and busyness of modern life in which leisure, work, and intimate relationships need to be juggled 12,23 ; and the supply of online entertainment that may compete with sexual activity. 12,16,23,24 Although these hypotheses could explain the decrease in frequency among partnered individuals, additional mechanisms may be associated with the increases in sexual inactivity observed in our study. For example, rates of depression and anxiety have increased among young US adults; US adolescents are increasingly postponing the start of adult activities, including sex and dating 25 ; and it has been hypothesized that the introduction of smartphones has resulted in less opportunity for and skills in real-world human interactions. 26 For women, sexual inactivity may also be associated with a greater prevalence of "hooking up" (which has generally been reported to be less pleasurable for women) 27 or potential increases in sexual aggression directed toward women. 28 Moreover, we found that men with lower income and those with part-time or no employment were more likely to be sexually inactive. These findings are consistent with literature showing associations between lower income and measures of sexual inactivity [12][13][14]29 and decreased appeal in the mating market for men. 30-33 Given the widening disparities in economic security (some of which are more pronounced among young men), 34 the preference for men of higher socioeconomic status, and the larger number of college-educated young women than men in the US, it has been suggested that a subset of young men find it difficult to establish themselves in the heterosexual mating market. 35-37 In our study, sexual inactivity in younger age groups was more common among men than women, and the increase in sexual inactivity was observed only among men identifying as heterosexual, although educational level was not associated with any measure of sexual activity, and being a student was associated with sexual inactivity among men and women.
Moreover, the increase in sexual inactivity among men remained after adjustment for changes in employment status.

Limitations
This study has limitations. First, we used survey data, which are subject to response and reporting bias. Second, because the data were cross-sectional, we could not assess temporality of the associations between sociodemographic factors and measures of sexual activity. Third, sexual activity was not defined in the General Social Survey. Thus, some participants may have interpreted the terms have sex and sex partners using a definition of vaginal intercourse (or sex partners as referring only to relational partners), whereas others may have considered sex to include oral sex or mutual masturbation. 38-40 Some studies 38,41 have found that men are more likely than women to report nonpenetrative sex as sex. As such, differences between the sexes and potential changes over time in the interpretation of the survey questions may have affected our findings. Fourth, we could not assess reasons for sexual inactivity and to what extent this was associated with satisfaction or dissatisfaction. In a US study, 29 sexually inactive individuals reported similar happiness levels as did those who were sexually active. In a British national survey, less than half of the sexually inactive participants aged 16 to 74 years reported dissatisfaction with their sex life. 14 Some individuals report never having felt sexual attraction to anyone 42 or a lack of interest in sex, 43 whereas others have difficulties in finding sexual partners, with this being a cause of distress. 44 To place our findings into context, further studies are needed on reasons for and potential feelings about sexual inactivity.