1Introduction

The National Children's Study (NCS) was congressionally mandated by the Children's Health Act of 2000. Section 1004 focuses on the National Children's Study stating, “it is the purpose of this section to authorize the National Institute of Child Health and Human Development (NICHD)¹ to conduct a national longitudinal study of environmental influences (including physical, chemical, biological, and psychosocial) on children's health and development.”²

The NICHD Office of the Director has primary responsibility for planning and coordinating the National Children's Study, the largest (100,000 children) and longest (before birth to age 21) study of environmental effects on children's health ever conducted in the United States. The NCS will examine the effects of the environment, broadly defined to include factors such as air, water, diet, noise, family dynamics, community and cultural influences, and genetics, on the growth, development, and health of children across the United States, following them from before birth until age 21. The goal of the study is to improve the health and well-being of children and contribute to understanding the role various factors have on health and disease.

Between 2005 and 2007, the research plan for the NCS was developed in collaboration among the Interagency Coordinating Committee, the NCS Advisory Committee, the NCS Program Office, Westat, the Vanguard Center principal investigators, and federal scientists.³ A review of this plan can be found in National Research Council (NRC) and Institute of Medicine (IOM) (2008). The current design uses a separate pilot (or “Vanguard Study”) to assess quality of scientific output, logistics, and operations and a “Main Study” to examine exposure-outcome relationships. The house-to-house recruitment strategy endorsed with qualifications by the 2008 panel of the NRC/IOM was tested in the Vanguard sites, resulting in recruitment of fewer pregnant women and births than originally estimated. The issues associated with sampling were further studied in the additional Vanguard sites. As the results from Vanguard sites became available, there was much discussion about the most effective sampling approach among the NCS Program Office, federal and non-federal sampling experts, Vanguard principal investigators, and others. Considering this input, the NCS proposed the use of a multilayered cohort approach for the Main Study, which was one of the topics for discussion at the workshop that is the subject of this publication.

In the fall of 2012, NICHD requested that the Committee on National Statistics (CNSTAT) of the NRC and the IOM convene a joint workshop, to be led by CNSTAT. The statement of task was as follows:

In preparation for the workshop, NCS provided a background paper to the steering committee (National Children's Study, 2012).⁴ The steering committee, collaborating by email and telephone, discussed the paper and the challenges to be addressed at the workshop, determined the agenda, and selected potential speakers. In addition, NCS and CNSTAT collaborated on the preparation of a more abbreviated workshop background paper that was distributed via the CNSTAT website in advance to all meeting attendees. The paper was referred to during the workshop as the Background Paper (and is cited in this publication as Kwan et al., 2013). The purpose of Kwan et al. (2013) was to explain the NCS and the status of the program and to pose specific questions for consideration at the workshop.

The Workshop on Design of the National Children's Study Main Study took place at the National Academy of Sciences on January 11, 2013. The three main topics addressed at the workshop were the collection of environmental exposure measures, the distribution of the sample among cohorts, and statistical issues associated with the sample design. These discussions, as outlined in Kwan et al. (2013), were intended to inform the NCS Program Office on specific design questions to guide the NCS Main Study, including considerations related to prenatal exposures, alternative approaches for collecting information, costs of such collections, and their value to analysis. The workshop was organized around four sessions, each with a specific set of questions to discuss. (The workshop agenda can be found in Appendix A, and a list of workshop registrants can be found in Appendix B.)

Each of the following four chapters is dedicated to one of the workshop sessions. The chapters begin with the information about the topic provided in Kwan et al. (2013) and the detailed questions posed by NCS. The chapters then summarize the main points of the panelists' remarks and the ensuing discussions. The overarching questions from Kwan et al. (2013) covered in each chapter are as follows:

• Chapter 2: Given the challenge as stated in the Children's Health Act of 2000 to “perform complete assessments of environmental influences on children's well-being,” does the proposed visit schedule and sample collection balance the complex requirements?
• Chapter 3: What should be the criteria for the cohort allocation decision and what evidence is available to support an assessment of each criterion? What should be the allocation of sample cases among the various cohorts?
• Chapter 4: Given the study design proposal described in Kwan et al. (2013), and using the example cohort proportions proposed in the Chapter 3 questions, what enhancements can be made to address estimation and imputation challenges?
• Chapter 5: From today's discussion, can you synthesize the tradeoffs among factors, issues, and values that need to be balanced and considered by NCS leadership?

This report was prepared by a rapporteur as a factual summary of what occurred at the workshop. The steering committee's role was limited to planning and convening the workshop. The views contained in the report are those of individual workshop participants and do not necessarily represent the views of all workshop participants, the steering committee, or the National Research Council/Institute of Medicine.