The first domain, which we call health conditions, contains information on disease, impairment, injury, and symptoms. Most of the items come from vital statistics (in the form of low birthweight and death by cause data), from clinical or administrative data as reported on claims or encounter forms, from injury reporting systems, or from registries. Some surveys also collect data on proxy-reported (or occasionally, in the case of adolescents, on self-reported) health conditions, injuries, and impairments. There are differences in the ways that the principal data agencies (i.e., CDC, NCHS, MCHB, and AHRQ) define specific diseases and measure them. Also, agencies use different age categories, even within childhood. As a result, the country has various estimates for the prevalence of health conditions, making it difficult to compare sources of data regarding conditions and to understand reasons for the differences in estimates.
Another concern is that the cumulative data from most surveys provide estimates for prevalence, but not for the incidence, of individual diagnosed conditions, and there is little information about the overall health of individual children. That is, surveys often look at one or two disease entities, rather than a profile of how diseases cluster in groups of individuals. Diseases are not randomly distributed in the population (Starfield, 1991; Kunitz, 2002), and an accumulating literature (Starfield, 2001; Long et al., 1994) documents the magnitude of this co-occurrence (comorbidity), which is especially pronounced in childhood, when the overall prevalence of health conditions is low but unexpected co-occurrence of different types of illnesses and impairment is higher than would be expected by chance distributions (van den Akker et al., 1998).
Despite this knowledge, most data collection efforts do not describe or facilitate explanation of the clustering of health conditions in specific individuals or population subgroups. There is considerable and robust evidence that children with ongoing health conditions, such as asthma or diabetes, are more likely to have other types of conditions as well. For example, a large literature, for both adults and children, demonstrates that mental health problems are more common in children with chronic physical conditions than in the overall child population (Harris et al., 1996; Long et al., 1994; Stein and Silver, 2002). Thus another concern about the currently available data is that they focus on individual conditions, rather than on the health of groups of individuals.
Given the recent estimates by the surgeon general (U.S. Department of Health and Human Services, 1999) that approximately 1 in 10 (11 percent) of children of ages 9–17 have a significant behavioral or emotional disorder with substantial impairment in current functioning, it may be surprising that there are no assessment approaches currently in place that track child and adolescent emotional health in all of its important aspects.
Generally missing are data on physical and emotional symptoms. Both clinical records and surveys are potential sources of data on symptoms; their coding