the NCS goals and design are responsive to the call in the act for a “national longitudinal study of environmental influences (including physical, chemical, biological, and psychosocial) on children’s health and development.”

Conclusion 2-2: The large, nationally representative, equal probability sample design, together with the inclusion of a large number of outcome and exposure measures over a long time span, are major strengths of the NCS. In particular, the sample design is an appropriate platform for the study, considering resource constraints, the need to represent all population groups and geographic areas, and the difficulty of devising an alternative disproportionate sampling scheme that would not unduly disadvantage some groups and areas that turn out to be of analytical interest.

Conclusion 2-3: In four overarching areas, the NCS design, as represented in the research plan, is not, or may not be, optimal for achieving the goals of the Children’s Health Act. These areas are:

• insufficient attention to understanding disparities in child health and development among population groups of children defined by race, ethnicity, language, socioeconomic status, and geographic area, which the act explicitly mandates;

• inadequate conceptualization of important constructs, including health and development, and an overemphasis on disease and impairment relative to health and functionality and on risk factors relative to protective health-promoting factors;

• impaired data collection schedules and types of measures to support evaluation of some of the effects of chronic and intermittent exposures on child health and development; and

• underappreciation of the challenges to obtaining the highest possible quality of data from an observational design, which include the decentralized data collection structure of the study and limitations on the frequency of home and clinic visits and on the collection of medical and other administrative records for study participants.

Recommendation 2-1: The NCS should give priority attention to seeking ways to bolster the ability of the study to contribute to understanding of health disparities among children in different racial, ethnic, and other population groups, including the reestablishment of a working group to oversee this area and the encouragement of appropriate adjunct studies.