**4.3 Factors associated with prevalence**

Of many factors that have been tested for association with prevalence in general population studies, findings for gender, age, SES, and degree of urbanization will be discussed here, because those are factors with findings that have been replicated across studies (Achenbach & Rescorla, 2007).

*Gender:* Gender differences in prevalence are very robust across cultures, informants and across types of studies, in particular those that used rating scales and those that used DSM diagnostic criteria. Girls score higher than boys on internalizing psychopathology such as anxiety, depression and somatic complaints, and boys score higher than girls on externalizing behaviours such as attention and hyperactivity problems and aggressive and delinquent behaviours. These gender differences are found for both parent- and selfreported problems. Despite the range in cultural, economic, political and genetic differences, there is consistency in population-based findings that boys have more externalizing and girls have more internalizing problems.

*Age of children and adolescents*: From a developmental perspective, the effects of age on levels of psychopathology in individuals can best be studied through longitudinal studies. For public policy purposes, cross-sectional data on prevalence with age can be important for service planning. Age interacts with gender as a factor associated with prevalence. Boys show more problems than girls when they are younger, whereas girls show more problems than boys in adolescence (Achenbach & Rescorla, 2007). In a multicultural study of selfreported problems across 7 countries, both internalizing and externalizing behaviours increased with ages 11 to 18 years. In another multicultural study of parent-reported problems of children aged 6 through 11 years across 12 countries, and aged 6 through 17 years in 9 countries, externalizing problems decreased and internalizing problems increased with age (Achenbach & Rescorla, 2007). Although parents and adolescents agreed in reporting increases with age of internalizing problems, they disagreed about externalizing problems. Apparently parents are increasingly unaware of their child's externalizing behaviours with increasing age. This is probably caused by a developmental shift in type of externalizing problems, with overt physically aggressive and oppositional behaviours decreasing with age and status violations such as truancy, running away from home, and substance abuse increasing with age (Bongers et al., 2003).

*Socio-economic status:* Previous studies have shown that rates of psychopathology are higher among individuals with lower socioeconomic status (SES) than those with higher SES (e.g. Schonberg & Shaw 2007). Published findings regarding associations between parents' marital status, immigration, and child behaviour problems are rare, and fewer studies still have reported on these associations in early childhood (Javo et al., 2004). Achenbach and Rescorla (2007) summarize studies from 15 cultures that tested associations between scores on empirically based scales and measures of socio-economic status (SES) in large population samples. Measures of SES varied across studies, but most used the occupation and/or education of the child's parents and grouped participants into low-, medium-, and high-SES groups. A few studies also used measures of family income. Although the studies varied in statistical details, they were consistent in reporting higher problem scores for children from lower-SES than from higher SES (Verhulst, 1995; Waddell, 2002). Although this finding was consistent across studies, the effects were rather small. There are a number of reasons that may be responsible for the finding that children from lower SES are somewhat disadvantaged.

*Degree of urbanization:* Most studies investigating differences in prevalence rates between urban and rural populations did not find significant differences (Waddell et al., 2002). Achenbach and Rescorla (2007) conducted a detailed comparison of varying degrees of urbanization while controlling for sex, age, referral status, SES, region and ethnicity in a US national sample. Children from the most urban areas showed a slight tendency to obtain higher parent reported problem scores than children from the most rural areas. However, unexpectedly, the greatest contrast in problem scores was found between children in the intermediate categories versus those in the most rural areas, with highest scores for children in the intermediate categories.
