representing the domain or subdomain differ from one developmental stage to another.
It seems especially important to develop good tools to assess the health of children at major transitions, such as entry into preschool or the beginning of adolescence because these represent critical points at which potential health problems may interfere with the developmental tasks. Measurement strategies should be devised to elicit not only important milestones in development but also the trajectory of characteristics that affect the attainment of those milestones at expected times. For example, most children babble and make simple words before they start saying phrases, and they make declarative statements before they ask questions. But it is unknown how much the variation in the acquisition of those skills affects overall language development except in the most extreme situations.
Disparities in health by race and ethnicity are well documented (Institute of Medicine, 2002b, 2003) and demand national attention. A large subpopulation of children also has poorer health due to social disadvantage. Children in lower income families have more severe health problems and worse health prognoses than children in higher income families. Except for most large national surveys that collect data on family income and parental education, few or no data are collected to provide a systematic understanding of differences in health in population subgroups based on socioeconomic status.
In addition, there are specific subpopulations of children that deserve special attention because of their extra vulnerability to poor health. Localized studies and long-term follow-up studies of specific populations of children (e.g., children who are abused or neglected or in foster care) indicate that some have poorer health (including mental health) and more developmental problems and seriously compromised long-term health trajectories. At present there is limited systematic collection of health-related data on most of these subpopulations at either a local or a national level. A similar situation holds for children with special health care needs due to chronic and debilitating medical or mental health conditions, children in special education school systems, children with severe emotional and behavioral disorders, and institutionalized children. Each of these vulnerable subpopulations of children is poorly reflected in health measurement attempts. Moreover, most surveys intentionally exclude institutionalized children, many of whom have severe health impairments. The very small size of some of these special populations require targeted special studies.