Teenage pregnancy rates in the United States have declined since the early 1990s . This trend is thought to be partly a function of more consistent contraceptive use and later onset of sexual activity than in previous years . In 2002, 13% of females and 15% of males ages fifteen to nineteen reported having had sex before age fifteen, as compared to 19% and 21% respectively in 1995 [1, 3]. While an encouraging trend, these statistics mask higher prevalence of early and high risk sexual activity among certain populations. For example, the average age of sexual debut among inner-city youth is thirteen years of age, three years earlier than the national average . Additionally, African-American teens tend to initiate sex earlier than Caucasian or Latina teens, and are more likely to initiate prior to age thirteen than are Caucasian teens . Earlier sexual debut among minority populations contributes to ongoing health disparities, with rates of HIV, other sexually transmitted diseases (STDs), and unintended pregnancies disproportionately high among minority adolescents .
Previous studies have found that initiating sexual activity before age sixteen increases the likelihood of having an unintended pregnancy, inducing pre-cancerous changes in the cervix, and contracting STDs, including HIV/AIDS [5–12]. In spite of decreased teen pregnancy rates, 11% of all US births are among teenage girls and the teen pregnancy rate in the United States is two to eight times that of many other developed countries [13, 14]. Of new STD infections each year, 48% are among people ages fifteen to twenty-four years old . These consequences affect not only the adolescents themselves, but can incur a high cost to society through the need to support adolescent childbearing and its contribution to infant mortality .
In contemporary American society, what was once considered an early adulthood transition has arguably been evolving over the past several decades into anticipated behavior in middle and late adolescence . The links between sexual intercourse and numerous psychosocial factors, including substance abuse, low self-esteem, depression and suicide attempts have been found to be strongest among younger adolescents in the United States . Sexual intercourse may represent a marker of psychological distress when it occurs early, as opposed to at a more normative time . These findings speak to the vulnerability of young adolescents and the importance of examining the relationship between psychosocial factors and early sexual behavior.
Whereas correlations between demographic factors and adolescent sexual activity have been fairly robust in the literature, psychological and behavioral correlates of early sexual behavior are less well understood [12, 19]. This study is part of a larger research project related to adolescent development and is the second in a study of psychosocial risk factors associated with sexual onset among young urban, minority teens. In a cross-sectional study examining the sexual behavior of young adolescent girls, we found that sexually active girls under age sixteen endorsed significantly more symptoms of depression, had a more pessimistic outlook of their futures, felt less academically motivated, and did less well in school than those who were not sexually active . The current longitudinal study expands on that first study by including both genders and by examining potential causal links between hypothesized psychosocial risk factors for early and high risk sexual activity. Prospective studies such as this can help to identify incipient factors exerting influence over adolescent development  and also potentially improve interventions to reduce such health-compromising behaviors.
Given consistent associations between demographic factors and early sexual behavior, we have controlled for certain factors including socio-economic status (which includes family structure, parental education, and a proxy measure for economic status), peer pressure, and sensation-seeking behavior. Previous studies have shown that children who live with both biological parents are less likely to be sexually active than those from one-parent homes, that increased maternal education is associated with later age of adolescent first intercourse, and that as socio-economic status decreases, rates of sexual activity tend to increase . Other studies have examined peer influences on sexual initiation, concluding that perceived degree of peer sexual activity is directly related to adolescent sexual behaviors [23–26]. Likewise, sensation seeking behavior, defined as the tendency to pursue novel and stimulating experiences , has been reported as a factor also presumed to antecede sexual activity [23, 24, 28] We maintained separate variables for both genders in order to determine moderating effects of gender on the variables of interest.
Our study is informed by a conceptual framework that emphasizes the reciprocal relationship between three systems of influence on adolescent sexual behavior, including the self system, the familial system and the extra-familial system . We focus on the correlations between teenage sexual behavior and two variables within the self system, namely psychological and behavioral factors. To study the psychological and behavioral correlates of risky adolescent sexual activity, we have used an additional conceptual framework adopted from the field of child psychology which distinguishes between 'externalizing,' or disorders characterized by behavioral disinhibition (disruptive behavior disorders of childhood) and 'internalizing,' or disorders characterized by negative mood states and inhibition (depression, anxiety) [21, 29]. Our study seeks to apply this conceptual framework to examine how engaging in sexual risk behavior is influenced by internalizing factors, including depression, anxiety, and post-traumatic stress and by externalizing factors, including substance abuse, violent and non-violent delinquency.
Previous studies have identified several externalizing (or behavioral) and internalizing (or emotional) psychosocial factors influencing risky sexual behaviors among adolescents . In terms of externalizing behaviors, studies have examined teen sex in the context of sociological literature on "deviant behavior" (which is understood as behaviors which depart from the regulatory norms of conventional society defining appropriate behavior for that age or stage in life) [22, 30]. Some researchers have suggested that correlations between deviance and sexual behavior may be even stronger for younger initiators given that sexual intercourse at an earlier age is considered more deviant behavior than when it occurs at a more normative time . A theory elaborated by  regards teen sex as one of numerous risk-taking behaviors constituting a "problem behavior syndrome" associated with a constellation of problem behaviors such as smoking, drinking, drug use, and delinquent behaviors constituting low-level status offenses . Studies have found fairly consistent associations between externalizing problems such as conduct disorders (delinquency, aggressiveness, impulsiveness) and substance abuse (cigarette smoking, marijuana use, and use of other illicit drugs) and increased rates of early and high risk sexual behavior [29, 32, 33]. While associations between behavioral problems (aggression, delinquency) in childhood and increased risk of compromising sexual behaviors (including high rates of risky sex, frequent sexual activity, early sexual debut, low rates of condom use, high numbers of sexual partners, and high rates of prostitution and drug/alcohol use before and during sex ) has been well established in the literature, little is known about the factors and pathways that lead to such increased risk among adolescents who show signs of early conduct difficulties .
In contrast to robust associations between externalizing behaviors and adolescent sexual behavior, links between sexual behavior and internalizing factors have yielded mixed results [17, 29]. On the one hand, a review of literature by  found that internalizing problems (low self-esteem, depression, and anxiety) are related to low perceived self-efficacy, which in turn is associated with decreased assertiveness, minimal ability to negotiate safe sex with a partner, sexually permissive attitudes, having sexually active friends, high risk of pregnancy, low contraception use, and non-virgin status. Other studies have specifically correlated depressive symptoms to high-risk sexual practices (such as early onset and contraception non-use) and negative health outcomes (such as unintended teenage pregnancy and contracting a sexually transmitted disease) [4, 36]. On the other hand, other studies have found no significant effect between internalizing factors and risky sexual behavior in adolescence [29, 34] or identified very limited effects of psychosocial predictors such as self-efficacy on sexual behavior . Further definition of the relationship between mental health problems and adolescent sexual activity is vital because of the high rate of mental health problems which often take root in adolescence [38, 39] and the opportunities for potentially effective interventions.
The hypothesis tested in this study is that sexual activity and high-risk sexual behavior in early adolescence (ages eleven to fifteen) is an expression of underlying psychosocial strains. We hypothesize that externalizing and internalizing psychopathology progressing from early middle school will be associated with higher rates of early and high-risk sexual activity. To test these hypotheses, we have divided the study into two parts. Our first study question examines the unique effects of internalizing psychopathology and externalizing psychopathology on initiation of sexual activity in middle school; our second study question examines the effects of these risk factors on high-risk sexual behavior. Distinct from other longitudinal studies on this topic, we also will examine how the rate of change in the risk factors over the course of middle school is associated with early and high sexual risk behaviors during middle school.