Executive Summary
Physical aggression affects a significant segment of the Canadian population of children. Using data from the first collection cycle of the National Longitudinal Survey of Children and Youth we have estimated at 3.5 the percentage of 2- to 4-year-old children in the Canadian population who, according to the person most knowledgeable about the child, are physically aggressive. This percentage is nearly the same for boys between 5 and 11 years of age (i.e., 3.3 per cent) whereas it is substantially lower for girls (i.e., 0.6 per cent). Essentially, these children can be characterised by a propensity to manifest physically aggressive behaviours that is many times higher than that of the other children of the same age and sex in the Canadian population.
These results have important methodological implications. These results suggest that latent class analysis (LCA) could provide a unified framework for combining ratings on many behaviour symptoms to identify a set of mutually exclusive and exhaustive classes of individuals that differ markedly in their propensity to manifest the symptoms in question. Because LCA does that while taking into account the symptoms' lack of sensitivity and specificity it can be used to obtain unbiased estimates of the proportion of individuals in the population who belong to the various latent classes. Second, LCA can be used to predict latent class membership for each individual based on his or her observed ratings. Third, LCA can be used to compare the prevalence of behavioural or emotional problems across groups.
These results have important public policy implications. First, this study provides, for the first time, public health policy analysts with very precious information as to the prevalence of physical aggression in the Canadian population of children 2 to 11 years of age. We believe that these prevalence estimates should help to evaluate the need for mental health services for physically aggressive children at the national level. Second, this study provides a clear operational definition of what constitutes a physically aggressive child in Canada in terms of his or her propensity to manifest physically aggressive behaviours. We believe that this operational definition should help to design cost effective prevention and intervention programs that are adapted to the needs of physically aggressive children in Canada. Third, this study provides the means to identify physically aggressive children in Canada. We believe that these means should help to channel the scarce public resources for mental health services toward those most in need of them.
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