Design of the National Children's Study A Workshop Summary (2013) / Chapter Skim
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3 Sample Design - Consideration of Multiple Cohorts
3 Sample Design - Consideration of Multiple Cohorts
Pages 23-44
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From page 23... ...
BACKGROUND ON SAMPLING AND COHORTS Geographical Area Sampling The original National Children's Study (NCS) plan called for 105 primary sampling units (PSUs)
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From page 24... ...
The NCS is also piloting a few methods in the Provider-Based Sampling Vanguard sites to give some empirical data on acceptance, logistics, and costs. It is also possible in the birth cohort to attempt to collect medical records not only from the hospital or birth ing center, but also from the sample member's prenatal care provider (if any)
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The subsequently born children could have prospective documentation of preconception and prenatal exposures. The Prenatal Cohort is a sample of the prenatal care providers that are linked to the sampled hospitals or birthing centers from the birth cohort and a subsample of women who visit a prenatal care provider and ex pect to deliver at one of the selected hospitals or birthing centers.
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From page 26... ...
If the prenatal cohort were limited to women visiting the sample of prenatal care providers within a specified time period who were in their third trimester, then the enrolled population would likely cover close to the entire population of pregnant women who receive prenatal care. However, the NCS would not be able to obtain measures of exposures earlier in the pregnancy except to the extent medical records contained relevant information.
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From page 27... ...
By definition, a birth cohort will have more limited data on prenatal exposures than a prenatal cohort, while a prenatal cohort will have less information on prenatal exposures (and much less information on preconception exposures) than the cohort of subsequent births to already enrolled mothers or a separate preconception cohort.
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From page 28... ...
He said if NCS used an almost 100 percent birth cohort that enrolled subsequent sibling births, this would save even more costs than the current 50-50 split and would immeasurably increase the scientific value of the study when it is completed 21 years from now. Garfinkel said he and Bracken also agree that collecting prenatal data is a critical component of the NCS and that his own understanding
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From page 29... ...
Assuming that completed fertility is about 2 children, a birth cohort of first births would have sibling births with preconception and prenatal data on about the same number of births as a 100 percent prenatal cohort.
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If enrollment costs were $2,000 and prenatal data collection costs $18,000, the ratio would be 10 to 1. In other words, he said, for every child enrolled in a prenatal cohort, 3 to 10 children could be enrolled in a birth cohort for the same cost.
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From page 31... ...
Garfinkel concluded that his analysis identifies the key scientific questions underlying the choice between the size of the prenatal and birth cohorts: How important are early prenatal data? How important are preconception data?
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An alternative, D6, might be to take 40,000 from a birth cohort, 40,000 from a prenatal cohort, 10,000 from a sibling cohort, and maybe 10,000 from hot spots. Other designs might allocate the cohorts differently.
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From page 33... ...
He suggested integrating special cohorts into the overall design. The 10,000 special cohort may be from hot spots; however, it will likely be analyzed together with a main cohort comparing hot spot exposure to exposures among the general population.
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. She said that as a research associate at the then-new Center for Research on Child Wellbeing at Princeton University in 1997, she was involved in the new birth cohort study called Fragile Families.
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If a hospital encounter would still be needed for some reason, sampling from prenatal care providers would be enormously expensive compared to sampling from hospitals because of the added cost of the prenatal data collection encounters, access to both prenatal care providers and hospitals, and the logistics of coordinating the study across so many sites. She said key pieces of information are missing, including the cost of access and recruitment for prenatal care providers and hospitals, cost of obtaining placental material under both options, and detail about whether women in a prenatal cohort require a hospital evaluation.
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From page 36... ...
, but the causes will not be found in birth cohorts. Rather, he said, they are due to associations in pregnancy, including disparities in prenatal care, and only the prenatal cohort would provide the data to study these issues.
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He stated that collecting prenatal data only for children who already have a sibling would be a detriment to the NCS. He noted that biological exposures may not differ between first and subsequent pregnancies, but the scientific interest is in the interaction between these exposures and the fetus, and the fetus changes from one pregnancy to another.
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From page 38... ...
Although it has the significant disadvantage of including only preconceptions after a prior pregnancy, it may be the NCS' only feasible alternative to a preconception cohort before first pregnancies. Bracken emphasized that he sees no advantage to the birth cohort because, to him, it misses the unique opportunity offered by the NCS to study the most important scientific questions.
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From page 39... ...
He expressed his opinion that when all up-front costs are considered, NCS could get as many or more women with early prenatal data from the birth cohort with sibling follow up, because collecting prenatal data on the first birth is so expensive. Bracken replied that it is a matter of the scientific questions, not just cost.
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From page 40... ...
Bracken noted that with the birth cohort plus siblings, no real-time pregnancy data on first births are obtained, which he termed a dangerous position for the study going forward. In contrast, he noted that the pregnancy cohort would advantageously include first, second, third, and all other births.
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From page 41... ...
Some academic hospitals may participate, but he said he doubted many others would. Duan noted the sibling cohort does not necessarily have to come from a hospital birth cohort but could very well come from a prenatal cohort.
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From page 42... ...
Duan noted that PBS, a combination of the prenatal cohort and what has been called the birth cohort, sounds like a very good approach. For the operation of the sibling cohort in the detection of pregnancy, he said some of his colleagues make use of information technology, such as mobile devices, to encourage or invite the participants to send feedback to the study when an important event occurs.
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From page 43... ...
Sara McLanahan (Princeton University) asked how well the two sampling cohorts generate good representative samples based on actual cooperation and response rates.
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From page 44... ...
McLanahan asked about the importance of eight-week first-trimester measures. If the provider sample can do as well on response rates, this provider cohort might be preferable because it would result in more data on prenatal care.
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