The National Children's Study 2014 An Assessment (2014) / Chapter Skim
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2 Study Design
2 Study Design
Pages 27-44
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From page 27... ...
It also describes overarching issues that drive the sample design, including two of the key topics the panel was asked to consider: the national probability sample's overall sample size and design and the relative size of the prenatal and birth strata in the probability sample. The chapter also provides the panel's analysis of a third key topic the panel was asked to consider: the proposed uses of supplemental convenience samples to enroll nulliparous women for preconception data collection and to enroll additional populations to address targeted research questions.
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From page 28... ...
. In considering its assigned topics regarding the NCS study design, the panel found it useful to draw from many of these ongoing studies to delineate design principles and guidelines that would optimize the scientific value of a longitudinal birth cohort study of child health and development such as the NCS (e.g., Golding, 2008; Olsen, 2012)
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From page 29... ...
For the NCS, these include estimating relationships between exposures and health outcomes, analyzing health disparities, and attaining representation of children in key demographic and geographic subgroups roughly in proportion to their representation in the population. • As large a sample size as possible within budget constraints is needed to provide statistical power for current and future scientific discoveries.
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From page 30... ...
Second, emerging research on the early origins of future health points to the importance of early postnatal, prenatal, and even preconception conditions, which implies concentrating data collection in the early years relative to the later years of the study. These paradigms of developmental biology and life-course epidemiology, coupled with insights from a number of social and behavioral sciences, should guide development of the NCS study design.
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From page 31... ...
Exemplar Hypotheses The process of using a scientific framework and context to guide decisions regarding the NCS study design, sampling frame, and data collection protocols can be facilitated by identification of scientifically robust exemplar hypotheses. In the case of the NCS, this means hypotheses that encompass current and anticipate future scientific inquiry concerning high-priority environmental factors and child health and development outcomes, while accounting for potential confounding and effect modification.
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From page 32... ...
A possible rationale for unequal selection probabilities arises from the NCS's charge to address health disparities, which by definition involve disadvantaged population subgroups. But, as discussed below and in Chapter 3, we believe that the large size of the main NCS sample, along with careful stratification, will provide sufficient statistical power to investigate health disparities
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From page 33... ...
The current NCS Program Office design is to enroll roughly half of its sample prenatally and half at birth. Several major national birth cohort studies have enrolled women during the prenatal period and collected biological specimens at multiple points during pregnancy, including Generation R, a large population-based Dutch cohort (Jaddoe et al., 2012)
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From page 34... ...
Enrollment at the time of birth should be limited to women who do not receive prenatal care or otherwise do not have a chance of selection through prenatal providers. RECOMMENDATION 2-2: In order to facilitate scientific discovery dur ing and after National Children's Study data are gathered, the Main Study should use a national probability sample with the largest feasible sample 6 For a description, see http://www.env.go.jp/en/chemi/hs/jecs/ [May 2014]
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From page 35... ...
However, the cost information for the multiple components of the Vanguard Study may not be directly relevant to evaluating future costs because the Vanguard Study spent significant time and resources to conduct large scale pilot testing of multiple recruitment strategies and data collection protocols. The Vanguard Study has or should yield relevant information for designing the Main Study, although some additional pilot testing may be needed to address gaps in information.
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From page 36... ...
In response, the current plan describes a detailed conceptualization of health and development. The breadth of the conceptualization would encompass most of the issues affecting child health and development and provide many dimensions that could be linked to environmental exposures, which should facilitate scientific discovery.
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From page 37... ...
SUPPLEMENTAL SAMPLES Given the scientific value of the largest possible national probability sample, the panel carefully considered NCS's current plan to allocate a portion of its total sample to supplemental or "convenience" samples.7 Specifically, the NCS Program Office proposes a probability sample of 90,000 births and supplemental samples of 10,000 births and seeks advice about the optimal composition of the 10,000. The plans as of October 25, 2013, were as follows (NICHD, 2003d, pp.
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From page 38... ...
Preconception Sample for First Births Given the emerging scientific importance of prenatal and even preconception conditions for later health and development, the potential value of NCS information on preconception exposures could be quite high. The NCS Program Office proposes that the main probability sample include both its targeted births plus roughly 8,000 siblings of the targeted children born later during the 4-year birth window (see details in Chapter 3)
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From page 39... ...
can be analyzed using the prenatal environmental information gathered for first births that occur in the main sample. The effects of important preconception exposures, whether persistent or not, that have similar effects on first and subsequent births can be analyzed using preconception data gathered from the sibling sample.
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From page 40... ...
Our cost analysis illustrates the opportunity costs of the preconception sample by showing that eliminating the preconception first birth sample would enable almost complete prenatal, rather than the currently planned half prenatal and half postnatal, recruitment of women and children in the main sample. RECOMMENDATION 2-5: While the panel appreciates the potential scientific value of gathering preconception exposure information on 5,000 first-birth children as part of the National Children's Study Main Study, this supplemental sample should be dropped because of high costs, the lack of any evidence of the value of such a sample, the lack of detailed plans for both selection and analysis, and potential limitations in the pro posed data collection schedule.
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From page 41... ...
In addition, the needed coordination of sample design and study staffing between the probability sample and geographic exposure samples dictates that sample selection and recruitment for the geographic sample should begin at roughly the same time as sample selection and recruitment for the Main Study. Given the study's expected mid-2015 start date and that the Program Office has not yet identified the specific geographic exposures of interest that it would target, the panel fails to see how data collection for the geographic exposure sample could coincide with the data collection for the probability sample.
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From page 42... ...
. RECOMMENDATION 2-6: The supplemental convenience samples pro posed for the National Children's Study Main Study should be dropped from the design, including samples of children exposed to natural disasters or geographically defined environmental exposures, samples of additional members of disadvantaged groups, and samples of siblings born outside the 4-year birth window.
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From page 43... ...
devote resources to retain as many participants as possible in the Main Study. Although the panel agrees that the large sample size and the comprehensive assessment of health determinants and health outcomes that is planned in the NCS will allow researchers to investigate many important health disparity questions, the relevance of health disparities to children and society, as well as the high importance of this topic to the NCS, requires that the NCS take special steps to ensure that the sample is adequate for addressing these questions.
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