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Social, emotional and behavioural difficulties have different prevalence levels over the course of childhood. Overall, levels of difficulties, and particularly those meeting diagnostic criteria, increase in the general population the older children get (e.g., (Skovgaard et al., 2005; Green et al., 2005; Fleitlich-Bilyk & Goodman, 2004)). For example, in the British Child and Adolescent Mental Health Survey, prevalence of a mental disorder was 12% in 11-16 year olds compared with 8% for 5-10 year olds (Green et al., 2005). However, research following-up children regularly between the ages of 9 and 16, suggests that these wide age bands may hide more subtle differences between years: the overall prevalence of disorders found was highest in 9-to 10-year olds, falling to the lowest levels at age 12, before gradually increasing again (Costello et al., 2003).

Different disorders/ types of symptoms follow different trajectories. In terms of internalising disorders, such as depression and anxiety, levels have generally been found to be low across early to middle childhood (Toumbourou, Williams, Letcher, Sanson, & Smart, 2011; Waxler, Dougan, & Slattery, 2000). Waxler reported rates of depression of less than 1% in preschoolers, 2% in school-aged children and rates of 2-8% in adolescence, with a dramatic increase shown

between the ages of 15 and 18 (Waxler et al., 2000). In contrast, in a community sample of children in Australia, researchers explored internalising symptoms measured at eight time points between ages 3 and 15 and saw a steady decline in mean scores of internalising behaviours. However, they identified a specific

32 group of girls with increasing trajectories of internalising behaviours, which predicted depression scores in late adolescence (Toumbourou et al., 2011). A further study following boys between the ages of two and ten, found that four distinct trajectories could be seen in the development of anxiety disorders: low, low-increasing, high-increasing and high-declining. Evidence showed that shyness in the early years accounted for much of the variation between high and low levels of anxiety. This was exacerbated in both groups over time by maternal depression and maternal negative control (Feng, Shaw, & Silk, 2008). It is worth noting, however, that those rating behavioural (and other) difficulties are likely to be using their experience of children of a particular age as the reference group for reporting difficulties. The importance of this is that difficulties at certain ages, for example behavioural problems in two year olds, may be down- played as this is simply seen as being ‘normal’ at a particular age. There may be a more pronounced pattern of difficulties therefore than reported.

Peer relationship problems demonstrate an increasing prevalence for most children during early to middle childhood, which is consistent with the view that, as children age, they spend more time interacting with peers and therefore are more likely to experience negative peer experiences (Barker, Boivin, & Brendgen, 2008; Biggs et al., 2010). Studies have shown an overall increase in the likelihood of being a victim of bullying between the ages of 3 and 7 years old, as reported by teachers and children (Barker et al., 2008), with further increases between the third and fifth years of school (Biggs et al., 2010). However, prevalence of bullying in the US was higher among children in the 6th

to 8th Grades, compared with older children in the 9th and 10th Grades (Nansel et al., 2001).

In relation to externalising behaviours, longitudinal studies following children from infancy have found that a majority of children display some kind of aggression towards family or friends in infancy, but most will learn ways to regulate the use of physical aggression before the start of school. Tremblay and colleagues have produced a body of evidence around such trajectories using data from Canada. Evidence showed that boys’ levels of conduct problems were

either stable or declining from age six onwards (Nagin & Tremblay, 2001). A further study identified two groups of children who had either a moderate increasing trajectory of aggression, or a high-risk trajectory. The latter was

33 linked to a series of adverse circumstances in childhood, such as living in a low income household, family dysfunction and coercive parenting, as well as having a mother with a history of anti-social behaviour (Tremblay et al., 2004).

Importantly, analyses of trajectories of physical aggression have found no

evidence of a late onset of such problem behaviours, suggesting that children on problematic aggression trajectories can be identified by the start of school (Brame, Nagin, & Tremblay, 2001).

Anti-social behaviour trajectories have been argued to show both a life course persistent pathway and an adolescent onset trajectory, both for boys and girls. Girls were more likely than boys to be in the adolescent-onset group in relation to anti-social behaviour (17.4% of girls vs. 12.3% of boys), though the majority of children had either persistent low levels of anti-social behaviour or declining levels of anti-social behaviour from mid-childhood (these two groups

representing approximately three-quarters of children) (Odgers et al., 2008). Hyperactivity disorders follow similar patterns to conduct problems, showing decreasing frequencies as a function of age (Shaw, Lacourse, & Nagin, 2005). A study of six to fifteen year old boys showed that the majority of boys followed a low or moderately declining trajectory of hyperactivity with just 6% following a chronically high hyperactivity trajectory (Nagin & Tremblay, 1999b). The main difference from that of conduct and aggression problems is the slightly later onset of hyperactivity disorders: the peak age of diagnosis of hyperactivity disorders is at 7-9 years old (McGee, Williams, & Feehan, 1992), though again this could be related to age referencing, with hyperactivity in younger children being seen as developmentally ‘normal’.

8.1.3.1Stability of individuals’ social, emotional and behavioural difficulties over time

In terms of stability of difficulties, it has been suggested that children with a history of psychiatric diagnosis are three times more likely to have a subsequent psychiatric diagnosis, compared with children with no history of mental health problems (Costello et al., 2003). It is worth pointing out that there are two types of continuity in mental health problems: homotypic and heterotypic. Homotypic continuity, which most studies including the current one focus on, is the

34 child; whilst heterotypic ‘suggests an underlying vulnerability to psychiatric illness that may expose children to different disorders at different ages or an underlying disorder that has different manifestations at different ages’ (Costello et al., 2003).

Focusing on homotypic continuity, some conditions appear to be more stable over time than others. Aggression has been found to be relatively stable

throughout childhood and adolescence (Pouwels & Cillessen, 2013b; Moskowitz, Schwartzman, & Ledingham, 1985). Tremblay found that children with chronic Oppositional Defiant Disorder could be identified as early as kindergarten age (Tremblay, Duchesne, Vitaro, & Tremblay, 2013). Both problem behaviours and social competence have been found to remain stable in the first two years of school, according to both mother and teacher-rated reports (National Institute of Child Health and Human Development Early Child Care Research Network, 2003). Furthermore, recent evidence suggests that, for children who enter school with heightened levels of aggression, 65% had behavioural problems two years later (Kim-Cohen et al., 2005). Other evidence using teacher-reports of externalising behaviours found that these increased between kindergarten and 3rd Grade. This is counter to parent-rated trajectories of the same measure, which tend to decrease over time (Silver, Measelle, Armstrong, & Essex, 2005). Furthermore, issues such as victimization and bullying demonstrate inconsistent results with regards to the stability of difficulties over childhood. Whilst some studies have evidenced peer relationship problems to be far less stable in early (Barker et al., 2008) and middle childhood (Pouwels & Cillessen, 2013a), other studies have produced evidence of a high level of stability in bullying and victimisation, though only for boys: Finnish evidence shows a strong degree of continuity of victimisation and bullying, respectively between ages 8 and 16, however the same did not hold true for girls, where bullying showed very little stability and only half of girls who were victimised at age 16 were also victims at age 8 (Sourander, Helstelñ, Helenius, & Piha, 2000). There is also a suggestion from some studies that bullying is more stable than being a victim, and that both bullying and victimisation are more stable for boys than for girls (Camodeca, Goossens, Terwogt, & Schuengel, 2002).

35 Among 9-16 year olds, the most stable conditions were found to be panic

disorders, psychosis, verbal tics, encopresis (when toilet-trained children

continue to soil their clothes) and enuresis (inability to control urination – often nocturnal i.e. bedwetting). This study also found that girls, although having lower levels of disorders across the board, had the highest levels of continuity (Costello et al., 2003).

The stability of internalising symptoms, such as anxiety and depression, in early childhood continues to be a source of great debate. Internalising symptoms in preschool aged children has been found to be relatively stable (Perren,

Stadelmann, von Wyl, & von Klitzing, 2007). Evidence focusing on children aged 2 to 11 years old reported that the majority of children followed fairly stable trajectories of internalising symptoms between these ages, however, there was a group of children whose symptoms decreased during early childhood and a group whose symptoms increased during late childhood (Sterba, Prinstein, & Cox, 2007). Recently, it has been argued that anxiety and depression cannot be distinguished from each other until adolescence (Wichstrom et al., 2012; Moffitt, Harrington, & Caspi, 2007). This view is backed by evidence which show that children who experienced anxious solitude and peer exclusion in preschool show relative stability in their difficulties five years later, and were also more likely to experience depressive symptoms at this point (Gazelle & Ladd, 2003). Further evidence suggests that children who are socially withdrawn in preschool are at risk of internalising problems at age 9-10 (Rubin, Hymel, & Mills, 1989). Moffitt explored the overlap of anxiety and depression in a longitudinal study in the first 32 years of life. Results showed that anxiety preceded depression in 32% of cases, whilst depression preceded anxiety in 37% of cases, with 72% of lifetime cases of Generalised Anxiety Disorder also experience Major Depressive

Disorders, indicating that it may not just be in childhood that these two sets of internalising symptoms are difficult to untangle (Moffitt et al., 2007).

Furthermore, it has been argued that the separation of depression and anxiety as discrete disorders was purely to create new licensing opportunities for the pharmaceutical industry (Shorter & Tyrer, 2003). The SDQ used in the current study contains depressive symptoms and anxiety-related symptoms in the same scale of Emotional Symptoms, so this overlap is taken account of.

36 Not only are there overlaps between anxiety and depression, but there are

significant overlaps between other areas of social, emotional and behavioural difficulties during childhood. The following section explores further the overlap between different difficulties.