J Youth Adolescence DOI 10.1007/s10964-015-0292-2

EMPIRICAL RESEARCH

Understanding the Link Between Pubertal Timing in Girls and the Development of Depressive Symptoms: The Role of Sexual Harassment ¨ zdemir1 • Ha˚kan Stattin1 There´se Skoog1 • Sevgi Bayram O

Received: 25 February 2015 / Accepted: 24 April 2015 Ó Springer Science+Business Media New York 2015

Abstract The link between sexual maturation, or pubertal timing, in girls and adolescent depressive symptoms is well-documented, but the underlying processes remain unclear. We examined whether sexual harassment, which has previously been linked to both pubertal timing and depressive symptoms, mediates this link, using a two-wave longitudinal study including 454 girls in 7th (Mage = 13.42, SD = .53) and 8th grade (Mage = 14.42, SD = .55). Pubertal timing was linked to depressive symptoms in both age groups, and predicted an increase in depressive symptoms among the 7th graders. Sexual harassment significantly mediated the link between pubertal timing and depressive symptoms among the 7th, but not the 8th grade girls. Together, our findings suggest that one way to prevent depressive symptoms among early-maturing girls could be to address sexual harassment in preventive intervention in early adolescence. Keywords Puberty
Pubertal timing
Internalizing problems
Depressive symptoms
Sexual harassment
Female development

& There´se Skoog [email protected] ¨ zdemir Sevgi Bayram O [email protected] Ha˚kan Stattin [email protected] 1

Center for Developmental Research, School of Law, ¨ rebro University, 701 82, Psychology and Social work, O ¨ rebro, Sweden O

Introduction The prevalence of depressive symptoms, such as feelings of hopelessness and worthlessness, increases drastically during adolescence. This is currently a major public health concern throughout the world (Bor et al. 2014; O’Connell et al. 2009). Adolescent girls are about twice as likely to be affected compared to boys (McGee et al. 1990). Scholars in several countries, including the US (Hamilton et al. 2014), Canada (Tre´panier et al. 2013), the UK (Joinson et al. 2011), Finland (Kaltiala-Heino et al. 2003), and Norway (Wichstrøm 2000), have identified puberty, specifically pubertal timing, as a central factor in the drastic increase in girls’ depressive symptoms during adolescence. Girls who enter puberty before most of their same-age and same-sex peers have a significantly higher risk of developing depressive symptoms during the early stages of adolescence (Negriff and Susman 2011). Although the link between early pubertal timing in girls and adolescent internalizing problems is well-documented, it still needs to be more fully understood. Specifically, there is still insufficient understanding of the underlying processes that contribute to internalizing problems of earlymaturing girls. Given that early pubertal timing has been linked to adolescent depressive symptoms irrespective of prepubertal levels of depressive symptoms (Black and Klein 2012), there must be mechanisms other than mere stability underlying the link between pubertal timing and depressive symptoms in early adolescence. Understanding the mechanisms underlying the link between early pubertal timing and adolescent internalizing problems is crucial not only for theory development, but also for the development of effective preventive interventions. If we are able to identify the mechanisms behind the pubertal timing-depressive symptoms link, we have the chance to target these

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mechanisms, and thus reduce the likelihood of early-maturing girls becoming depressed both during adolescence and later in development. For prevention purposes, such mechanisms or risk factors need to be malleable. In this longitudinal study, we examined whether sexual harassment (i.e., unwanted sexual attention) is a mechanism underlying the link between pubertal timing and depressive symptoms among girls during early stages of adolescence. This conceptual model (Allison and Hyde 2013) builds on two solid findings in the literature, which until now have not been connected explicitly. First, past research has found that when girls experience puberty (i.e., menarche) before most of their same-age peers (Skoog and ¨ zdemir 2015) or when they perceive themselves Bayram O to be developing earlier than their same-age peers (Goldstein et al. 2007) they are more likely to be sexually harassed in early to mid-adolescence. Second, both crosssectional (Lichty and Campbell 2012) and longitudinal studies (Chiodo et al. 2009) have shown that adolescents who are sexually harassed display a wide range of internalizing problems, including aspects of depressive symptoms. In the present study, we employed a developmentally sensitive design and examined the proposed process from pubertal timing via sexual harassment to depressive symptoms among 7th and 8th grade girls using a multigroup path model. We employed this approach given that the rapid quantitative and qualitative transitions occur throughout the first part of adolescence (Chumlea et al. 2003) and given that the link between early pubertal timing and depressive outcomes differs between grades 7 and 8 according to earlier (Ge et al. 2001) and more recent studies (Joinson et al. 2011). Puberty, Pubertal Timing, and Depressive Symptoms Puberty is a hormonally-driven biological process with psychological and social meaning. Although puberty is a universal transition, girls differ markedly with respect to how old they are when they experience it. In a large body of cross-sectional and longitudinal research, early pubertal timing, typically measured using age at menarche, has been linked to various forms of internalizing problems among adolescent girls (see Negriff and Susman 2011 for a review). For instance, in a large scale UK-based prospective study, Joinson et al. (2011) found that earlier menarche was linked to higher levels of depressive symptoms on the short mood and feelings questionnaire at ages 13 and 14 years. In a well-designed longitudinal French Canadian study, Tre´panier et al. (2013) found that, compared to girls maturing on time (age at menarche between 12 and 13 years), early-maturing girls (age at menarche between 10 and 11 years) displayed significantly higher levels of

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depressive symptoms on the Child depression inventory. According to some research, but not all (Ge et al. 1996), the increase in depressive symptoms among early-maturing girls seems to take place in the early stages of adolescence rather than the later (Rudolph et al. 2014), with the difference between early- and later-maturing girls being established at least by age 12.5 years. Moreover, past research has revealed that the link between pubertal timing and depressive symptoms among adolescent girls is linear rather than curvilinear (Benoit et al. 2013). Thus, studies from different countries using different measures of depressive symptoms have converged on the finding that earlier menarche is linked to depressive symptoms during the first half of adolescence and that the symptoms develop at or have developed by the beginning of adolescence.

A Psychosocial Explanatory Model of the Link Between Pubertal Timing and Girls’ Depressive Symptoms Several models have been proposed to explain why earlymaturing girls are more likely than their peers to suffer from depressive symptoms. Psychosocial explanations, which have received the most attention among developmental scientists (Mendle et al. 2007), highlight the changes in the social context resulting from early pubertal maturation as the underlying reason for the link between pubertal timing and depressive symptoms. Early maturation is assumed to elicit social changes, such as new expectations from adults and new peer networks, which girls are not adequately prepared to handle. Deviating from the norm could also be difficult in itself. Empirical studies support psychosocial explanations and indicate that compared to later-maturing peers, early-maturing girls are more exposed to peers spreading rumors about them (Reynolds and Juvonen 2011) and chronic stress within other-sex relationships (Llewellyn et al. 2012). Past research has also shown that early maturers have heightened sensitivity to dating (Natsuaki et al. 2009), stressful aspects of friendships and general peer relationships (Conley and Rudolph 2009), and peer rejection (Silk et al. 2014). Specifically, cross-sectional (Llewellyn et al.) and longitudinal research has found that peer stress partially mediates the link between early pubertal timing and internalizing problems, including depressive symptoms in girls (Conley et al. 2012). Taken together, these findings suggest that peer stress and peer victimization are potentially valid psychosocial explanations of the link between pubertal timing and depressive symptoms among adolescent girls. Although empirical studies have found peer stress and peer victimization to mediate the link between pubertal timing and

J Youth Adolescence

depressive symptoms, as explanations these factors are very broad and general. A functional neuroimaging cross-sectional study including 48, 11–17 year-old adolescents (50 % clinically depressed) indicated that irrespective of age, with progressing puberty (i.e., adrenarche), adolescents showed more peer rejection sensitivity (Silk et al. 2014). In that study, however, girls and boys and their respective measures of pubertal maturation were combined. Given the important developmental differences between boys and girls, the findings need to be viewed as preliminary. Moreover, it is not readily apparent from the prior studies why early-maturing girls should be more exposed to peer victimization compared to later-maturing girls. For instance, early-maturing girls are not more likely than peers to be involved in bullying (Jormanainen et al. 2014) and, perhaps more importantly, in a review of the literature the authors concluded that early-maturing girls are more popular among peers (Waylen and Wolke 2004). This latter statement has been confirmed in more recent research showing that early maturing girls are perceived, by their teachers as well as by their same and other-sex peers, to be more popular (Reynolds and Juvonen 2011). In addition, early-maturing girls themselves feel more popular among (opposite-sex) peers (McCabe and Ricciardelli 2004). Thus, instead of having an inferior position in the peer group, these studies suggest that early-maturing girls have high social status among peers. General peer stress or peer victimization might therefore be a too imprecise explanation. In this study, we extended this explanation by focusing on a psychosocial risk that is specifically related to the main obvious characteristics related to pubertal timing, namely changes in their physical appearance and sexual development.

Sexual Harassment as an Alternative New Explanation of the Link Between Pubertal Timing and Depressive Symptoms Early-maturing girls are the first in their same-age peer group to experience the emergence of secondary sexual characteristics during puberty (e.g., breasts and the hourglass body shape). These overt changes signal sexual maturity to the social context, and consequently these girls stand out in a clear and sexual maturity-related way among their physically immature peers (Pellegrini 2001). This means that others are more likely to react sexually towards them in ways that include unwanted sexual advances: sexual harassment. The earlier girls mature, the more likely they are sexually harassed. In past research, early-maturing girls were more likely to report being the victim of sexual harassment during the early to mid-adolescent years

compared to their peers (Petersen and Hyde 2009). Moreover, pubertal timing is linked to when girls start engaging in sexual activities, with early-maturing girls engaging in such activities earlier than their peers (Baams et al. 2015). In turn, risky activities, including early sexual activities, are linked to sexual victimization (East and Hokoda 2015), and having many sexual partners early in adolescence is linked to an increased risk of sexual harassment (Kennair and Bendixen 2012). This is possibly because sexually active girls are likely to be alone with boys who might harass them or pressure them sexually or because girls who are known to be sexually active may be viewed as willing sex partners or sex objects, which could lead to harassment. Being sexually active and, to a greater extent, having a sexually-mature appearance seem to be main reasons why pubertal timing is linked to being sexually harassed in early ¨ zdemir 2015). Moreadolescence (Skoog and Bayram O over, it is possible that for the very reason that early maturers are more popular among same-age peers (Reynolds and Juvonen 2011) they are at a higher risk for sexual harassment. Sexual harassment is defined as ‘‘unwanted sexual attention’’ (McMaster et al. 2002, p. 92) and is constituted of both the offender’s behaviors and the victim’s psychological subjective perceptions. It could be anything from name calling to physical sexual abuse. Sexual harassment is distressing and has detrimental psychological implications for the victims. Cross-sectional studies have shown that sexually harassed youth have poorer school performance (Lee et al. 1996), more psychological distress (Lichty and Campbell 2012), and more shame about the body (Lindberg et al. 2007) compared to non-harassed peers. In addition, sexual harassment is linked to worse mental health than what bullying is (Gruber and Fineran 2008). Longitudinal research has shown that sexual harassment increases the risk not only of future sexual victimization but also of internalizing problems such as eating disorders (Petersen and Hyde 2013), self-harm, and suicidal thoughts (Chiodo et al. 2009). Given that earlymaturing girls are more likely to be sexually harassed, and that sexual harassment is linked to future internalizing problems, it is possible that sexual harassment mediates the link between early pubertal timing and depressive symptoms. This mediation model was recently proposed by Allison and Hyde (2013, p. 62). They argued that sexual harassment may lead to depressive symptoms in early-maturing girls partly because they may lack effective tools to cope with the harassment, which they may get only later in development. Although Allison and Hyde claim that sexual harassment should be an important mediator in the link between early menarche and psychological symptoms, the model has never been empirically tested.

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The Present Study

Methods

The aim of this longitudinal study was to examine whether sexual harassment mediated the link between early female puberty, measured by age at menarche, and depressive symptoms. Early-maturing girls suffer from higher levels of depressive symptoms in adolescence compared to peers and they are also more often the target of sexual harassment. Given that sexual harassment is distressing and linked to future psychological problems, including depressive symptoms, it could be a mediator in the pubertal timing-depressive symptoms link (see Allison and Hyde 2013). Whereas the link between early female pubertal timing and sexual harassment and the link between sexual harassment and the development of internalizing problems are both well-established in research, the full developmental pathway from early pubertal timing via sexual harassment to depressive symptoms has not been tested empirically. Moreover, the model may not be equally valid throughout adolescence. Because adolescence, particularly the first part, is characterized by rapid quantitative and qualitative physical, psychological, and social transitions, the model may only apply to a certain developmental period. Accordingly, previous research has found that the link between early pubertal timing and depressive outcomes differ between ages 13 and 14 (Joinson et al. 2011). We therefore employed a developmentally sensitive design and examined the proposed process from pubertal timing via sexual harassment to depressive symptoms in a multi-group path model (i.e., across 7th and 8th grade girls). We used age at menarche as our measure of pubertal timing. The research questions were: (1) Does pubertal timing contribute to the depressive symptoms of adolescent girls over time?, and (2) Does sexual harassment mediate the link between pubertal timing and depressive symptoms? We expected that there would be a concurrent association between earlier pubertal timing and greater depressive symptoms and that pubertal timing would contribute to the development of depressive symptoms. We also expected that being exposed to sexual harassment would mediate the effect of early pubertal timing on the development of depressive symptoms over time. Prior studies have found that general peer victimization or peer stress mediates the link between pubertal timing and depressive symptoms (Conley et al. 2012). Because our aim is to build on and extend this previous model, we included general peer harassment, a construct that captures stressful peer relations and victimization in the peer group, as a second mediator in our statistical model (see Fig. 1). Thus, we examine whether sexual harassment mediates the link between pubertal timing and depressive symptoms over and above the mediating effect of general peer harassment.

Participants

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The sample of the current study came from a 4-year cohortsequential longitudinal study (the Seven School Study, Trifan and Stattin 2015) examining young people’s experiences across home and school contexts that potentially affect their emotional, social, and behavioral adjustment. The study was conducted in a medium-sized Swedish city with a population of 130,000. Seven schools were selected from neighborhoods with varying socio-demographic characteristics, and students from the 7th to 9th grades were targeted in each school. These students were followed annually until they finished secondary school (i.e., from the 7th to the 9th grade). In the present study, we used data from the second and third assessments. At the second assessment of the data collection, i.e., the first wave which was used in this study, the target sample comprised 1654 adolescents, 89 % of whom participated in the study. Among the participating adolescents, 67 % were 7th and 8th grade students (N = 1000). The analytical sample of the present study included 7th (n = 224, Mage = 13.42, SD = .53) and 8th grade girls (n = 230, Mage = 14.42, SD = .55) with data on pubertal timing. A majority of the girls (88 %) were born in Sweden and also had parents who were born in Sweden or in a Nordic country (70 and 69 % for mothers and fathers respectively). More than half of the girls were from intact families and lived together with both of their parents. A majority of them (91 %) also perceived their household financial situation to be as good as that of other families in their neighborhood. Attrition Analysis To examine whether the attrition (13 %, n = 59) between the two data collection waves was due to a systematic reason, we conducted a logistic regression analysis and regressed attrition (dropout = 1, retention = 0) on adolescents’ demographic characteristics (age and gender) and all other study variables (pubertal timing, sexual harassment, general peer harassment, and depressive symptoms). None of the variables significantly predicted attrition in both 7th and 8th grade students (Nagelkerke R2 = .058 and .061, respectively), implying that attrition would have minimal effect on our results. Procedure The data collection took place during regular class hours. Trained research assistants provided information to the students before the data collection on various topics,

J Youth Adolescence

Fig. 1 Mediating role of sexual and general peer harassment for the effect of pubertal timing on depressive symptoms. Note. Values on the left-hand side are the standardized estimates for 7th grade

students, and those on the right-hand side are for 8th grade students. T1 and T2 are separated by 1 year. *p \ .05; **p \ .01; ***p \ .001

including the goals of the study and the duration of the data collection process. Students were informed that their participation was voluntary, their responses were confidential, and they could withdraw from the study whenever they wanted. We included students in the data collection only if they and their parents agreed to participate in the study. A Regional Ethics Review Board in Sweden approved the study procedure.

things about you on for example walls, toilets, the blackboard, lockers or other places?’’ ‘‘Has anyone criticized you about personal matters, and told you that you are a brain, loser, geek, freak, nerd, immature, retarded, dull, dork, idiot, mongoloid or things like that?’’ They rated these questions on a 5-point scale, ranging from ‘‘1’’ (Never) to ‘‘5’’ (Daily). The inter-item reliability of this scale was .80.

Measures

Sexual Harassment

Pubertal Timing

A seven-item scale was used to measure the girls’ experience of sexual harassment (Marshall et al. 2013). In a section about peers and school in the questionnaire, girls were provided with a stem question (‘‘Have you been exposed to the following this school semester?’’) and were asked to respond to each of the seven questions on a 5-point scale ranging from 1 (‘‘Never’’) to 5 (‘‘Every day’’). The sample questions included: ‘‘Has anyone commented on your looks or your body in a sexual way that you don’t like?’’ and ‘‘Has anyone fondled or touched your body in a sexual way that you don’t like?’’ This scale has been shown to have good psychometric properties ¨ zdemir 2015), and had a strong inter(Skoog and Bayram O item reliability (a = .85) in the present study.

We used age of menarche to measure the girls’ pubertal timing, similarly to previous recent research on the link between pubertal timing and depressive symptoms (e.g., Tre´panier et al. 2013; Vaughan et al. 2015). Girls were asked to respond to a single question—‘‘How old were you when you had your first period?’’—on an 8-point scale, ranging from 1 (‘‘before the age of 10’’) to 8 (‘‘have not gotten my period’’). General Peer Harassment A five-item scale was used to measure girls’ experience of general peer harassment at school (Trifan and Stattin 2015). Girls were presented with a stem question (i.e., Have you been exposed to the following this school semester?’’). Then, they were asked to respond to each of the five questions such as ‘‘Has anyone written derogatory

Depressive Symptoms We used the Center for Epidemiological Studies Depression Scale for Children (CES-DC; Faulstich et al. 1986) to

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measure depressive moods among the girls. The CES-DC includes 20 items, 16 measuring depressive feelings (e.g., ‘‘During the last week, I was bothered by things that usually do not bother me’’ and ‘‘During the last week, I felt like people did not like me’’) and four assessing well-being (e.g., ‘‘During the past week, I felt like I was just as good as other friends’’ and ‘‘I was happy’’). Similar to previous ¨ zdemir and Stattin 2014), we only used research (Bayram O the 16 items measuring depressive feelings in the current study. The girls rated each item on a 4-point scale, ranging from 1 (‘‘Not at all’’) to 4 (‘‘Often’’). The CES-DC has been shown to have strong inter-item reliability and to be valid across different cultural contexts, including Sweden ¨ zdemir and Stattin 2014; Olsson and von (Bayram O Knorring 1997). In the present study, Cronbach’s alpha was .93 at T1 and .94 at T2.

Results

Data Analysis

Does Pubertal Timing Contribute to Depressive Symptoms of Girls Over Time?

To test our first research question (i.e., does pubertal timing contribute to the depressive symptoms of girls over time?), we estimated regression models and regressed girls’ depressive symptoms from their age of menarche which was measured 1 year earlier and controlled for the assessment of depressive symptoms 1 year earlier. To test our second research question (i.e., does sexual harassment and/or general peer harassment mediate the link between pubertal timing and depressive symptoms?), we fitted a multi-group mediation model in Mplus (Muthe´n and Muthe´n 1998– 2010), and tested the mediating roles of the girls’ experience of sexual and general peer harassment. The fit of the mediation model was evaluated on the basis of recommended model fit indices, including non-significant robust scaled Chi square statistic (S-Bv2), a minimum CFI of .90 and an ideal of equal to or [.95, and SRMR \.08 (Hu and Bentler 1999; Tabachnick and Fidell 2001). The observations in our data were clustered in classrooms, and so we controlled for clustering effect in order to eliminate biased standard error estimates and resulting inflated Type-I error. In addition, our mediator and outcome variables (i.e., sexual harassment, general peer harassment, and depressive symptoms) were positively skewed. Thus, we used robust maximum likelihood estimators, which provides standard errors and v2 test statistic that are robust to non-normality, in all our models (Muthe´n and Asparouhov 2002; Yuan and Bentler 2000). To handle the missing data issue, we employed the full information maximum likelihood estimation approach, which has been shown to be robust in estimating less biased standard errors compared to mean imputation, listwise, or pairwise deletion methods (Little and Rubin 2002; Schafer and Graham 2002).

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Descriptive Statistics and Preliminary Analyses Among 7th grade girls, about 3 % reported that they started to menstruate before the age of 11, and 76 % of them attained menarche between the age of 11 and 14, with a median age of 13 years. A similar distribution was observed among 8th grade girls, where 5 % had their first menstruation before 11 years and 90 % attained menarche between the ages of 11 and 14, with a median age of 12 years. More than half of the girls (62 and 64 % for 7th and 8th grade girls respectively) reported being exposed to some type of sexual harassment. As shown in Table 1, all the study variables were associated with each other in the expected directions across age groups.

The results of the regression analyses showed that pubertal timing significantly predicted 7th grade girls’ experience of depressive symptoms over time (b = -.14, p \ .05). Specifically, the earlier a girl experienced puberty, the more she felt depressed over time. No such association was observed among 8th grade girls. These findings suggest that pubertal timing contributes to the development of depressive symptoms among 7th grade girls, but not 8th grade ones. Does Sexual Harassment Explain Why Pubertal Timing is Linked with Girls’ Depressive Symptoms? We fitted a multi-group mediation model to examine whether being exposed to sexual and/or general peer harassment mediated the link between pubertal timing and depressive symptoms. The proposed mediation model was fitted in two steps. First, we estimated the mediation model for 7th and 8th grade girls simultaneously without imposing any equality constraints. The proposed model yielded a poor fit, with a significant S-Bv2(2) = 4.06, p = .04. After the inspection of modification indices, we added a direct path from pubertal timing to depressive symptoms at T2 in 7th grade girls, and refitted the model. The revised mediation model fitted the data well, S-Bv2(1) = 2.50, p = .11, CFI = 1.00, SRMR = .014. Standardized path coefficients are presented in Fig. 1. Our results showed that earlier pubertal timing was significantly liked to greater experience of sexual (b = -.21, p \ .001) and general peer harassment (b = -.21, p \ .001) in 7th, but not in 8th grade girls. In addition, sexually harassed 7th grade girls felt more depressed over time (b = .24, p \ .01). The tests

J Youth Adolescence Table 1 Means and standard deviations of and correlations among the study variables

1

2

3

4

-.21**

5

-.27***

SD

5.00

1.74

1. Pubertal timing—T1

–

-.21**

2. Sexual harassment—T1

-.15*

–

3. General peer harassment—T1

-.14*

.70***

4. Depressive symptoms—T1

-.13

.37***

.55***

5. Depressive symptoms—T2

-.19**

.29***

.40***

M

4.38

1.30

1.46

2.01

1.98

–

–

SD

1.28

.50

.61

.73

.71

–

–

.59*** –

-.23**

M

.35***

.38***

1.29

.44

.46***

.34***

1.41

.46

–

.40*** .61***

–

1.90

.65

1.76

.60

Correlations among the study variables and descriptive statistics for 7th grade students are presented above the diagonal; and those for 8th grade students are presented below the diagonal * p \ .05; ** p \ .01; *** p \ .001

of indirect effects revealed that sexual harassment significantly mediated the effect of pubertal timing on 7th grade girls’ experience of depressive symptoms over time (bind = -.05, z = - 2.41, p \ .05). That is, the earlier 7th grade girls matured, the more likely they were to be sexually harassed, and in turn feel more depressed over time. General peer harassment did not act as mediator in the link between pubertal timing and depressive symptoms in neither 7th nor 8th grade girls. Second, we added equality constraints on all the parameters estimated in the model. The fully constrained model had significantly poorer fit than the unconstrained model, Satorra–Bentler Dv2(9) = 27.83, p = .001, suggesting that magnitudes of some of the estimates in the model differed across 7th and 8th grade girls. Inspection of the direct paths across cohorts showed that the stability of depressive symptoms was significantly higher among 8th grade girls, and the magnitude of the effect of sexual harassment on depressive symptoms was significantly larger among 7th grade girls. The magnitude of the remaining direct paths did not significantly differ from each other across the two cohorts. Taken together, the results of the mediation analysis suggest that sexual harassment rather than general peer harassment is an explanation for the link between pubertal timing and experiencing depressive symptoms over time, particularly among 7th grade girls.

Discussion Around the world, adolescent girls suffer from depressive symptoms at higher rates than possibly ever before in modern history (Bor et al. 2014). Girls who enter puberty at early ages are particularly likely to suffer from such problems (Negriff and Susman 2011). Why is this? Although it is essential to effective prevention, the mechanisms underlying the link between pubertal timing and adolescent internalizing problems have still not been sufficiently understood.

Past research suggests that problematic peer relations play a role in the link between pubertal timing and girls’ depressive symptoms in adolescence (Conley et al. 2012). But, it has not been entirely clear why early-maturing girls should be more exposed to peer victimization compared to later-maturing girls. In fact, it has been concluded that early-maturing girls are more popular among peers (Waylen and Wolke 2004). We built this study on the theoretical model proposed by Allison and Hyde (2013) and corresponding empirical research. The previous research suggests that, the earlier girls experience puberty, the earlier they look more sexually mature and the earlier they become sexually active, and the more likely they are to be ¨ zdemir 2015) and sexually harassed (Skoog and Bayram O that adolescents who are sexually harassed display a wide range of internalizing problems, including aspects of depressive symptoms (Chiodo et al. 2009). Thus, we examined a unique form of problematic peer relations, namely sexual harassment. This longitudinal study extends previous research by examining the full, mediational pathway from pubertal timing to depressive symptoms via sexual harassment among 7th and 8th grade girls. To take prior findings into consideration and to understand the unique effect of sexual harassment as opposed to other forms of peer victimization, we included general peer harassment as a second mediator in our model. Our first hypothesis, that early pubertal timing would be linked to more depressive symptoms, was supported for both 7 and 8 grade girls. This finding adds to the large body of research that has demonstrated that girls who experience pubertal changes before most of their peers are more likely to suffer from depressive symptoms (Negriff and Susman 2011). Also supporting our first hypothesis and recent longitudinal studies (e.g., Joinson et al. 2011; Tre´panier et al. 2013), we found that early pubertal timing predicted an increase in depressive symptoms among 7th grade girls. This finding is in line with previous research showing that early pubertal timing is linked to adolescent depressive

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symptoms irrespective of prepubertal levels of depressive symptoms (Black and Klein 2012), and that once the comparatively high levels of depression have been established among early-maturing girls in early adolescence, there is no further increase in depressive symptom levels (Rudolph et al. 2014). Transitory effects of pubertal timing on psychological outcomes are consistent with some but not all empirical evidence. For instance, past research suggests that the link between pubertal timing and internalizing problems is transitory and that it dissipates over the course of adolescence (Joinson et al. 2013). However, in line with other studies (Copeland et al. 2010), we found that the link between early pubertal timing and depressive symptoms endured at least until grade 8. It appears that something of a biological, psychological, and/or social nature happens in the early phases of adolescence as a consequence of or in relation to pubertal timing, which makes girls who mature earlier than peers to be particularly prone to developing feelings of hopelessness, worthlessness, and other depressive symptoms. What is this ‘‘something’’? In this study, we proposed that being exposed to sexual harassment linked to the link between pubertal timing and the development of depressive symptoms. Specifically, we predicted that there would be a longitudinal pathway from pubertal timing via sexual harassment to depressive symptoms. In support of the second and main hypothesis, we found that being exposed to sexual harassment significantly mediated the link between pubertal timing and depressive symptoms over a year later, when controlling for depressive symptoms at baseline. This, however, was only the case for girls in grade 7. Although pubertal timing was linked to experiencing depressive symptoms among grade 8 girls, this does not seem to be due to experiencing sexual harassment. General peer harassment, which in prior studies has been found to mediate the link between pubertal development and depressive symptoms (Conley et al. 2012), did not uniquely mediate the link between pubertal timing and depressive symptoms in any of the cohorts. To summarize, both hypotheses were supported: early-maturing girls displayed higher levels of depressive symptoms in grade 7 and 8 and being exposed to sexual harassment, rather than general peer harassment, explains why early-maturing girls, particularly those at 7th grade, experience depressive symptoms over time. This study extends and goes beyond previous research on the role of social victimization or peer harassment in the link between pubertal timing and depressive symptoms among girls. Other longitudinal studies have shown that peer stress acts as a mediator in the link between pubertal timing and depressive symptoms in girls (Conley et al. 2012). However, to our knowledge, no longitudinal studies

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have considered multiple or different types of peer harassment as mediators of the link between pubertal timing and depressive symptoms. In the present study, we tested two different forms of peer harassment, general peer harassment and sexual harassment. We found that sexual harassment mediated the link between pubertal timing and depressive symptoms among grade 7 girls. General peer harassment, on the other hand, did not uniquely mediate this link. Thus, the current research sheds new light on the role of peers in the link between pubertal timing and girls’ depressive symptoms in suggesting that sexual harassment, rather than general harassment is a mechanism underlying the well-established finding that early-maturing girls are more prone to develop depressive symptoms compared to their peers in adolescence. An unexpected finding was that sexual harassment did not predict an increase in depressive symptoms among girls in grade 8. In line with prior studies (Lindberg et al. 2007; Lichty and Campbell 2012), sexual harassment and depressive symptoms correlated positively in the bivariate analyses. However, in the mediation model that included depressive symptoms at baseline, sexual harassment did not predict depressive symptoms over time. This finding is in contrast to the literature indicating that sexual harassment links to future emotional distress even when controlling for baseline levels of emotional distress (Chiodo et al. 2009). The high stability in depressive symptoms among the girls in 8th grade compared to girls in 7th grade (rs = .61 and .40, respectively) could be one methodological explanation for the null finding. Many of the girls who displayed depressive symptoms at the second wave (i.e., in grade 9) had already developed depressive symptoms by at the first wave (i.e., in grade 8). Perhaps some of these had already been sexually harassed earlier, and had developed their depressive symptoms partly because of that reason. Unfortunately, we cannot test this explanation against the study by Chiodo et al. because those authors did not report stability estimates of emotional distress levels. Clearly, future research is needed to shed light on this unexpected finding. We built this study partly on the idea that early-maturing girls signal sexuality at a time when their same-age peers do not, and that this is a reason for why they are sexually ¨ zdemir harassed (Pellegrini 2001; Skoog and Bayram O 2015). An alternative explanation for why early-maturing girls are more exposed to harassment by peers is that they exhibit more annoying behavior. Scholars have suggested that experiencing puberty earlier than one’s peers is distressing and that this distress makes girls act in disturbing ways in social contexts; this, in turn, brings out offending behaviors in peers that target the early-maturing girls (Schreck et al. 2007). A variant of this explanation was recently tested empirically (Jormanainen et al. 2014). The

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authors of that study examined whether there was a link between pubertal timing and girls’ involvement in bullying, but failed to identify such a link. Thus, early-maturing girls’ own annoying behavior does not seem to be an alternative explanation of why they are more (sexually) harassed by their peers. Limitations and Strengths This study has limitations that should be considered when interpreting the results. First, our model only included two mediators, general peer harassment and sexual harassment. We were not able to establish the unique effects of these mediators in relation to other mediators, for instance psychological ones. We could, however, establish that sexual harassment mediated the link between pubertal timing and depressive symptoms in grade 7 over and above what could be explained by general peer harassment, which has been a mechanism in focus in past research (Conley et al. 2012). In our model, there was a significant direct path from early pubertal timing to depressive symptoms. Our explanation, sexual harassment, could not explain this path, nor could general peer harassment. Clearly there are other mechanisms underlying the link between pubertal timing and depressive symptoms. Second, whereas our model included depressive symptoms at two time points, sexual harassment was only included once. Consequently, we could not address the direction of effects between sexual harassment and depressive symptoms. A possible alternative to our conclusion is that depressive symptoms predict sexual harassment over time. Third, we did not have a specific research question or hypothesis regarding how school or any other context plays a role in why early-maturing girls experience depressive symptoms. In the broader literature, the contextual amplification hypothesis focuses on contextual conditions, at different levels, which are assumed to attenuate or intensify the effects of early puberty on development (Ge and Natsuaki 2009). This comprehensive hypothesis suggests that early maturation is more likely to result in internalizing problems or other types of problems in adverse social contexts, such as disadvantaged neighborhoods. For the sake of the present study, it is possible that contextual factors, such as the school climate, moderate the link between pubertal timing and sexual harassment. It should be noted that using large data sets with a sufficient number of schools would definitely advance the field to uncover the role of the school context on the experience of early-maturing girls and their likelihood of being sexually harassed and, in turn, develop depressive symptoms. Finally, given that this is the first investigation of sexual harassment as a mechanism underlying earlymaturing girls’ mental health, the findings should be interpreted with caution.

Despite these limitations, the present study has several strengths. First and foremost, to our knowledge, this is the first study to empirically investigate whether sexual harassment, a common form of victimization in adolescence, could be a reason why early-maturing girls display and develop higher levels of depressive symptoms in early adolescence. The model was built on solid theoretical (Allison and Hyde 2013) and recent empirical evidence ¨ zdemir 2015). (Chiodo et al. 2009; Skoog and Bayram O Compared to previous studies that investigated peer stress and peer victimization more generally (e.g., Conley et al. 2012), we focused on a social risk specifically related to the main characteristics of early-maturing girls. Importantly, we included general peer harassment, a construct that captures stressful peer relations and victimization in the peer groups in our statistical model, but the results revealed that, in contrast to sexual harassment, general peer harassment did not uniquely mediate the link between pubertal timing and depressive symptoms. Second, the study had a longitudinal design, and we used state-of-the-art statistical techniques (e.g., bootstrapping) to reach robust conclusions. Third, focus group interviews were performed at the data collection sites prior to the larger data collection and these, in combination with the literature (e.g., McMaster et al. 2002), formed the basis of the design of our measure of sexual harassment. Because this contextsensitive measure uses language that is sensitive to the particular sociolinguistic context, the likelihood of capturing sexual harassment in this particular environment was high. In conclusion, the present study contributes uniquely to the literature on the link between pubertal timing and depressive symptoms by providing a new explanation of the link and using an advanced and robust context-sensitive methodological design to test this explanation. Implications for Future Research and Practice More studies are needed to understand the link between sexual harassment and depressive symptoms over time among adolescent girls. Future research should also test the unique indirect effect of sexual harassment in relation to other mediators, including other forms of victimization. The current findings have the potential to inform policy and practice. Around the globe, societies are struggling to find effective preventive interventions targeting internalizing problems among adolescents. It was recently shown that an incredible 54 % of all girls display high levels of anxiety and depressive symptoms (i.e., indications for clinical treatment) at least once during the latter half of adolescence (Patton et al. 2014). The earlier girls mature, the more prone they are to develop such problems. In order to decrease the high incidence of depressive symptoms starting from early adolescence (O’Connell

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et al. 2009), it is particularly important to develop preventative interventions that are tailored for the early-maturing group of girls. To the extent that sexual harassment causes depressive symptoms among early-maturing girls, prevention efforts should be aimed at reducing sexual harassment against adolescents. We recommend that such efforts or interventions include emotional and social skill training, as proposed by evidence-based social and emotional learning programs (Collaborative for Academic, Social, and Emotional Learning 2014). Such interventions could potentially increase socially respectful behavior and thus reduce the likelihood of sexual harassment. Moreover, the developmentally informed and evidence-based resources provided by, for instance, the Sexuality Information and Education Council of the United States (2014) could be used in practice and policy making in attempts to prevent sexual harassment aimed at all adolescents, not ¨ zdemir just early-maturing girls (see Skoog and Bayram O 2015).

Conclusions In this longitudinal study, our findings indicate that pubertal timing contributes to the development of depressive symptoms among 7th grade girls, but not 8th grade ones. Further, they suggest that being exposed to sexual harassment rather than to general peer harassment explains why early-maturing girls, particularly those at 7th grade, experience depressive symptoms over time. Thus, sexual harassment should be the target of preventive intervention in early adolescence or even before. It should be noted that we do not claim that we have found the only explanation for the robust link between pubertal timing and girls’ depressive symptoms. In fact, the current findings suggest that we have not. We acknowledge the vast literature that has identified other potential underlying mechanisms (Graber 2013). The optimal scientific approach to this topic would be a comprehensive longitudinal design including biological, psychological, and social mediators on many levels and their interactions in addition to the use of multiple measures of pubertal timing (e.g., hormonal, physician’s examinations, subjective). In the meantime, this study and its findings should be taken as revealing one piece—and a preventable one—in the puzzle of why experiencing pubertal changes before one’s classmates affects the mental health of adolescent girls and increases their risk of developing significant psychological distress. Acknowledgments This work was supported by a grant received by the first author from the Swedish Crime Victim Compensation and Support Authority (02847/2013).

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Conflict of interest

The authors report no conflict of interests.

Ethical standard The Regional Ethics Review Board approved the study procedures. Informed consent All participants were informed about and consented to take part in the study. Author contributions T.S. conceived of and designed the study, and coordinated and drafted the manuscript; S.B.O. participated in the study’s design, performed the statistical analyses, and participated in drafting the manuscript; H.S. conceived of the study, designed the original longitudinal research program, and helped with the writing of the manuscript. All authors read and approved the final manuscript.

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There´se Skoog, Ph.D. is associate professor at Center for Develop¨ rebro University. This manuscript was finalized mental Research, O when she was a visiting researcher at the Department of Psychology at The Norwegian University of Science and Technology (NTNU) in Trondheim. Her main research interests are normative physical development (e.g., puberty) in adolescence and related psychosocial adjustment, and prevention. She is currently directing a study on sexual harassment in early adolescence. ¨ zdemir, Ph.D. is a postdoctoral researcher at Center Sevgi Bayram O ¨ rebro University. Her research for Developmental Research, O interests include understanding the role of family, social, and cultural influences on children’s and adolescents’ adjustment, with an emphasis on migration context. ¨ rebro and Ha˚kan Stattin, Ph.D. is professor in psychology at O Uppsala universities, Sweden. He has worked in large longitudinal studies on the development of children, adolescents, and young adults across a variety of adjustment issues (antisocial behavior, delinquency, depression, shyness, anxiety, psychopathic traits, and civic engagement), ‘‘healthy functioning’’ and protective factors, crime prevention, parent–child interactions and communication. Especially his work on parental monitoring, knowledge and adolescent disclosure, as well as pubertal maturation has become well-known.