During the past several months the panel has met and reviewed the research plan for the National Children’s Study (NCS), various working papers of the study, and additional documents provided by the National Institute of Child Health and Human Development. The panel believes that this landmark study offers an unparalleled opportunity to examine the effects of environmental influences on child health and development, as well as to explore the complex interactions between genes and environments. The database derived from the study will be valuable for investigating the hypotheses described in the research plan as well as additional hypotheses that will evolve.
The critique, suggestions, and recommendations offered in the preceding chapters, therefore, are intended to improve the capabilities of the study to carry out the important mandate of the Children’s Health Act of 2000. This chapter highlights the panel’s key conclusions and recommendations resulting from its review organized by chapter and subject area.
CHAPTER 2: NCS GOALS, CONCEPTUAL FRAMEWORK, AND CORE HYPOTHESES
Conclusion 2-1: The stated overall and specific goals for the NCS—and the design of the NCS to achieve those goals—largely reflect the stipulations of the Children’s Health Act of 2000. In the broadest terms, 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.
Recommendation 2-2: The NCS should seek resources and develop methods to obtain more frequent in-person measures and medical and other administrative records data on study participants.
Recommendation 2-3: The NCS should clearly define the key constructs of child health and development and more fully develop a conceptual framework for understanding child health and development over the course of infancy, childhood, and adolescence.
Using the Vanguard Centers as Pilots
Recommendation 2-4: We strongly urge the NCS to delay enrollment at new sites to make effective use of initial findings from participant enrollment and data collection in the Vanguard Center sites to improve study procedures, as appropriate, and to refine key concepts, hypotheses, and measures of outcomes and exposures. Throughout the life of the study, the NCS should use the Vanguard Centers to pilot test and experiment with data collection methods and instrumentation.
CHAPTER 3: PRIORITY OUTCOME AND EXPOSURE MEASURES
Recommendation 3-1: The NCS should consider replacing research on subclinical maternal hypothyroidism as a factor in adverse pregnancy outcomes with research on the effects of a broader set of maternal physical and mental health conditions, such as maternal depression, maternal perceived stress, and maternal periodontal disease.
Recommendation 3-2: The NCS should develop refined, detailed protocols for investigating all pregnancy outcomes, specifically a detailed protocol for obtaining information on various types of pregnancy loss, before beginning data collection at the Vanguard Centers, given that pregnancy outcomes are among the first outcomes to be examined; many outcomes lack clarity in measurement; and there are important questions regarding the adequacy of statistical power and the planned data collection (for example, the need for prepregnancy measurements of some exposures).
Neurodevelopment and Behavior and Child Health and Development
Recommendation 3-3: The NCS should develop a clearer rationale for the selection of specific neurodevelopment and behavior disorders to be considered in the study and a clearer conceptual basis for the assessment of normal child health and development trajectories and outcomes. Clarity is needed to guide the choice of outcome measures and exposure measures and the frequency and types of contacts (at the home, in clinics) with study participants in order to obtain the best information possible within resource and burden constraints.
Recommendation 3-4: The NCS should develop a clearer rationale for its hypotheses about factors that may increase the incidence of asthma. These should focus on prenatal and early life risk factors.
Obesity and Growth
Recommendation 3-5: The NCS should reevaluate its main hypotheses to be addressed in the study of childhood obesity and consider adopting a broader approach that incorporates social and psychological factors as well as biogenetic ones. Such an approach would help the study identify the constellations of key factors and their interrelationships that are important to understand in order to develop the most effective public health measures to reduce childhood obesity.
Recommendation 3-6: The NCS should consider replacing research on repeated mild traumatic brain injury (rMTBI) with more nuanced research on other injury-related topics, such as environmental factors in childhood injuries and the effects of clinical response to injury (treatment or nontreatment).
Hormonally Active Agents and Reproductive Development
Recommendation 3-7: The NCS should develop refined and detailed protocols for studying reproductive development outcomes, which, as presented in the research plan, often lack clarity in measurement and research design. Outcomes that are measured at birth for which there is little time to refine research protocols require immediate attention. The NCS should use results from the Vanguard Centers, such as estimates of the prevalence of specific reproductive development outcomes, to assist in protocol development, and it should consider the usefulness of substudies of high-exposure population groups.
Demographic and Socioeconomic Measures
Recommendation 3-8: The NCS should add to its well-planned battery of demographic and socioeconomic measures questions on immigrant generation, languages spoken, and, if possible, the legal status of the parents and child.
Chemical Exposure Measures
Recommendation 3-9: The NCS should consider the use of personal air sampling methods for a subsample of participating women and their children for measuring exposure to air pollutants.
Recommendation 3-10: The NCS should incorporate methodology to measure paternal exposure to environmental chemicals (both persistent and nonpersistent). More generally, the NCS should consider collecting for fathers, not only chemical exposures, but also biological samples and interview data on paternal characteristics that may affect children’s health and development to the same degree as it collects such information for mothers.
Physical Exposure Measures
Recommendation 3-11: The NCS should provide a clearer rationale for some of the housing and neighborhood conditions it proposes to measure and revisit its data collection plans to ensure that needed measures are obtained at developmental stages when children may be more vulnerable to risk factors. The goal should be a set of measures and data collection plans that are optimal with regard to analytic utility and response burden.
Psychosocial Exposure Measures
Recommendation 3-12: The NCS should reconsider its psychosocial measures to ensure that they will provide high-quality data for outcomes of interest for child health and development. In the face of resource and respondent burden constraints, the NCS should emphasize the quality and analytic utility of information, even if some measures must be dropped in order to substitute other assessments more desirable on various grounds.
Recommendation 3-13: The NCS should dedicate a portion of funds to support research and development of reliable and valid instruments of key psychosocial measures that are practical and economical to administer.
Biological Exposure Measures
Recommendation 3-14: The NCS should review some of the proposed measures of biological exposures, such as maternal glucose metabolism and child cortisol levels, to ensure that the proposed times for data collection are appropriate for capturing the underlying exposure.
Recommendation 3-15: The NCS should adopt a clear mechanism by which genetic association studies are internally and, optimally, externally validated before any results are published or released to the media. The NCS should also revise its proposed “established” candidate gene approach to take advantage of the new information emanating from the current wave of genome-wide association studies, with appropriate replication.
Recommendation 3-16: The NCS should consider consolidating its genetics studies in order to reduce costs and to coordinate the best science at the least cost to the project. One approach would be to simply collect the biological samples and properly store them for later genetic analysis when a better selection of polymorphisms and cost-effective genotyping across studies are possible.
Recommendation 3-17: The NCS should add measures of access to and quality of services, including medical care, education, child care, and services, as potential mediators of health and development outcomes and to improve the assessment of information obtained through maternal reports.
Recommendation 3-18: To facilitate linkages of NCS data with environmental exposures from other databases, such as measures of demographics, crime, government programs, and pollution, the NCS should develop a plan for geocoding the residential addresses from prebirth through adulthood of all participating children to standard census geographic units. In addition, the study should develop arrangements by which researchers, both inside and outside the NCS study centers, can access geocodes for respondent addresses and are encouraged to perform linkages and make their environmental information available to the NCS analysis community. Such arrangements must safeguard the confidentiality of NCS respondents.
CHAPTER 4: STUDY DESIGN, DATA COLLECTION, AND ANALYSIS
Conclusion 4-1: We strongly endorse the use of probability sampling to select the NCS national sample of births.
Conclusion 4-2: While we endorse the decision to select an equal probability national sample of births as a reasonable strategy given the many key scientific objectives of the NCS, we recognize that a proportionate representation of the study’s target population will result in estimates for some subgroups that are not as precise as they would be had those groups been oversampled.
Conclusion 4-3: The process of identifying births from a national sample of households is complex and subject to numerous sources of attrition of uncertain magnitude. Because of this, it will be difficult to predict how many households must be initially selected to produce a probability sample of 1,000 births in each of the NCS sites.
Recommendation 4-1: The NCS should consider modifying the sampling design to allow for flexibility in increasing the number of study participants in the event that the estimated number of screened households needed to reach 1,000 births per primary sampling unit (PSU) is incorrect.
Recommendation 4-2: The NCS should consider the proposed household enumeration approach to be experimental and should conduct carefully designed field studies to clearly establish the statistical and practical implications of the proposed adjudicated listing approach.
Recommendation 4-3: To ensure a diverse exposure profile in the sample, the NCS should consider a careful assessment of variation in ambient exposure to chemical agents within each PSU. If the set of segments in a PSU can be classified by combined exposure to a group of important chemical agents, this information could then be used to form varying exposure-level strata for segment sampling in each PSU and thus ensure a range of ambient exposure to relevant environmental agents.
Conclusion 4-4: The data collection model adopted by the NCS is complex, will challenge the abilities of the staff and coordinating center to achieve a uniform and consistent national data collection, and may compromise key study objectives.
Conclusion 4-5: The NCS research plan does not provide sufficient information on the use of data collection guidelines and quality-control procedures to enable evaluation of the planned implementation of a uniform national data collection system.
Conclusion 4-6: The NCS research plan does not address directly the issue of respondent burden, except to say that “some” effort is being made to reduce it, nor does the plan make clear the total number of hours the respondent must commit to the study. In particular, in light of the estimate of the interview length (4 hours) for the baseline interview, a critical collection for the study, the research plan pays little attention to respondent burden and its impact on the quality of the data.
Conclusion 4-7: The NCS research plan provides little information concerning best methods for sample recruitment to achieve initial and follow-up target response rates, sample maintenance and sample retention procedures for implementation at the study sites, community involvement plans consistent with the uniform implementation of data collection procedures, or contingency plans to support study sites that do not achieve target response rates.
Conclusion 4-8: The NCS research plan does not address the ongoing methodological needs of the study—to study data collection procedures and instruments, conduct experiments, and evaluate the quality of the survey operations and the quality of the data—nor does the plan make the best use of the Vanguard Centers.
Recommendation 4-4: The NCS should consider ways in which the survey data collection could be consolidated into a smaller number of highly qualified survey organizations.
Recommendation 4-5: Because of the complexity of the proposed organizational model for data collection and the difficulty of maintaining the quality and uniformity of data collection procedures across a large number of study sites, the NCS program office should establish and monitor strict standards for enrollment, retention, and data collection at each of the study sites and be prepared to take immediate corrective action if sites do not meet high-quality standards in data collection.
Recommendation 4-6: The NCS should prepare a plan for monitoring progress of the study in reaching its sample size goals. As part of the plan, the NCS should take advantage of the experience of the Vanguard Centers to evaluate initial enrollment rates, the effectiveness and potential respondent burden of the interview instrument, and the ability of the Vanguard Centers to obtain the required household environmental measures reliably.
Recommendation 4-7: To resolve issues that arise during data collection, the NCS should set aside sufficient resources to maintain an ongoing program of methods research and field experimentation. Among the issues that might be addressed in this research are the reliability and validity of previously untested survey questions and measurement strategies, the effectiveness of sample retention procedures, predictors of response outcomes associated with sample initial recruitment and subsequent annual retention, error implications of unit nonresponse, adjustment strategies for unit nonresponse, and methods for dealing with item nonresponse.
Data Analysis and Dissemination
Recommendation 4-8: The NCS should begin planning for the rapid dissemination of the core study data, subject to respondent protection, to the general research community and for supporting the use of the data after dissemination. The costs of implementing this plan should be estimated and set aside in future NCS budgets. Dissemination includes not only the publication of findings through reports and scientific papers and the production of documented data files for researchers, but also active support in the use of NCS data by the broadest possible range of qualified investigators.
CHAPTER 5: ETHICAL PROCEDURES AND COMMUNITY ENGAGEMENT
Criteria for Giving Information to Participants
Recommendation 5-1: The NCS should define the criteria and the process for deciding what individual clinical and research information, such as environmental assessments, test results, and survey scales, will be given to children and their families.
Protection and Release of Information
Recommendation 5-2: NCS and non-NCS investigators should be given equal access to the full NCS data as soon as they are cleaned and documented. To protect respondent confidentiality, all analyses should be performed with the kind of strict safeguards employed by the Census Bureau research data centers.
Recommendation 5-3: The NCS should engage communities in selected study implementation, data analysis, and data interpretation activities that go beyond recruitment. The NCS should consider requiring every study center to formulate a more detailed plan to engage and collaborate with local communities.
In summary, it is clear from our review that the NCS offers not only enormous potential, but also a large number of conceptual, methodological, and administrative challenges. In addition, funding uncertainties make it difficult to plan beyond the relatively short period for which funds have been appropriated. Like the scientists associated with the study itself, we are eager for it to succeed. We present our conclusions and recommendations in the hope that, as it goes forward, the NCS will achieve its intended objectives and serve as a model of methodological and substantive contributions to important scientific and policy discussions on children’s health and development.
National Academies Press (US), Washington (DC)
National Research Council (US) and Institute of Medicine (US) Panel to Review the National Children's Study Research Plan. The National Children's Study Research Plan: A Review. Washington (DC): National Academies Press (US); 2008. 6, Conclusions and Recommendations.