The impact of each Study visit and each assessment on the participants, Study personnel, and Study infrastructure.

Advisory Committee to the Director Working Group (ACDWG)

A working group of the chartered federal advisory committee established to assist the Office of the Director, NIH, in the making of major plans and policies, especially those related to the allocation of NIH funds and resources.

Alternate Recruitment Strategy (ARS)

See Recruitment Strategy/Recruitment Schema below.

Anthropometric Data

Physical measurements of body size, shape, and composition such as height or weight, waist circumference, skinfold thickness, etc.


A sample of biological material taken from the human body, such as blood, plasma, urine, saliva, tissue, etc.

Centers for Disease Control and Prevention (CDC)

The CDC is a federal agency within the U.S. Department of Health and Human Services. Its main goal is to protect public health and safety through the control and prevention of disease, injury, and disability.

Cognitive Assessment

A test of one's thinking capabilities. Cognitive function includes the processes by which an individual perceives, registers, stores, retrieves, and uses information.

Computer Assisted Personal Interview (CAPI)

An interviewing technique in which the study participant or the interviewer uses a computer to administer questions and capture the answers.

Direct Outreach Recruitment (DO)

Also known as Two-tiered (or Hi/Lo) Recruitment Strategy, Direct Outreach is a preferred term to describe this strategy that uses marketing, direct mail, and other referral techniques to enroll a broad-based population in larger geographic areas (SSUs) beyond the predefined geographic segments. The approach is similar in concept to the U.S. Census Short Form and Long Form, or the Canadian Longitudinal Study on Aging. The Low Intensity National Children's Study provides participants with web-based, mail-in, or telephone-based brief questionnaires administered at about every 6 months. From the pool of participants in the Low Intensity protocol, those living in predefined geographic segments (TSUs) are invited to participate in the High Intensity protocol, which follows the Study visit schedule as that of the other recruitment strategies, namely the EH and PB.

Enhanced Household-based Recruitment (EHBR)

During recruitment, this strategy utilized field workers who entered predefined geographic segments and contacted individuals and families at their residence. This strategy is similar to that used by the initial seven Vanguard Centers, but was enhanced through application of best practices from experience, targeted marketing campaigns, enhancement of additional sources of referral into the Study(such as health care providers, social clubs and organizations), and public events, as well as streamlined enrollment procedures.


Refers to participants who consented to participate in the Study.

Environmental Protection Agency (EPA)

The United States Environmental Protection Agency (EPA) is an agency of the U.S. federal government which was created for the purpose of protecting human health and the environment.


Assessment of the technical performance of an aspect of the Study visits logistics or infrastructure.

High Intensity/Low Intensity Dynamic Model (Hi/Lo)

Also known as Two-tiered Recruitment Strategy /Direct Outreach. See Direct Outreach Recruitment (DO).

Information Management System (IMS)

An integrated system or set of systems consisting of hardware, software, connectivity, and business rules that provides secure administrative, computational, telecommunications, and data collection and transmission functions.

Initial Vanguard Study (IVS)

The very first phase of the Vanguard Study, intended to serve as a pilot to inform the planning of the National Children's Study Main Study. In the context of Vanguard Study data, IVS refers to data collected in seven PSUs from January 2009 to September 2010, when the IVS ended. The IVS recruitment was based on area probability household sampling.

Institutional Review Board (IRB)

A committee established to review and approve research involving human subjects, to assure that the research is conducted in accordance with all federal, institutional, and ethical guidelines.

National Academy of Sciences (NAS)

A private non-profit organization in the United States established by an Act of Congress and charged with providing independent, objective advice to the nation on matters related to science and technology.

National Children's Study (NCS)

A longitudinal study to examine the effects of the environment and gene-environment interaction on the growth, development, and health of children across the United States from before birth until age 21 years.

National Institute of Child Health and Human Development (NICHD)

One of the National Institutes of Health (NIH) and part of the United States Department of Health and Human Services, the Eunice Kennedy Shriver National Institute of Child Health and Human Development funds and conducts research on topics related to the health of children, adults, families, and populations.


Refers to the combination of neurological, psychological and social factors, which affect and are affected by one another.

Office of Management and Budget (OMB)

An office within the Executive Office of the President that oversees the activities of federal agencies in the United States. The Paperwork Reduction Act of 1980 established The Office of Information and Regulatory Affairs within OMB to review requests it receives from federal agencies to collect information from the public.

Personally Identifiable Information (PII)

Information about an individual including (1) any information that can be used to distinguish or trace an individual's identity, such as name, social security number, date and place of birth, mother's maiden name, or biometric records; and (2) any other information that is linked or linkable to an individual, such as medical, educational, financial, and employment information.

Post Recruitment Follow-Up (PRF)

Refers to the final phase of the NCS Vanguard from March 2014 through December 2014. No new enrollments were allowed during this phase and a common set of protocol assessments was administered to all study participants in all study locations.

Pregnancy Probability Group (PPG)

A status assigned to age-eligible women identified during recruitment who are not pregnant but likely to become pregnant. In the Initial Vanguard Study, women were assigned to low, medium, high tryer (i.e., trying to become pregnant) or high non-tryer PPG status based on responses to a series of questions. The PPG status determined the periodicity of follow-up calls to determine if women became pregnant or if their PPG status changed. In the Alternate Recruitment Strategy phase, PPG status changed to tryer or non-tryer only.

Pregnancy Visit 1

First visit among pregnant enrolled women in ARS and PBS. Different from the pregnancy visit terminology used in the IVS (equivalent to T1 First or T3 First visits in IVS).

Pregnancy Visit 2

Second visit among pregnant enrolled women in ARS and PBS (equivalent to T3Prior in IVS).

Primary Sampling Units (PSUs)

Individual components into which the target population is divided for the first sampling stage. In the National Children's Study, PSUs correspond roughly to U.S. counties.

Probability Sampling

A sampling methodology where every person in the target population has a chance of being selected into the Study, and this probability can be calculated. Examples of probability sampling methodology are simple random sampling, systematic sampling, stratified sampling, sampling with probability proportionate to size, and multi-stage sampling.

Program Office (PO)

Refers to the National Children's Study Program Office

Provider-based Recruitment (PBR)

Alternate Recruitment Substudy strategy in which women are recruited from health care providers in contact with women who are or may become pregnant. Women who reside in predefined geographic segments are recruited from prenatal care provider offices.

Provider-based Sampling Feasibility Substudy (PBS)

An arm of the Vanguard Study. Provider-based Sampling arm features include (1) county as the Primary Sampling Unit (PSU), 75 (2) providers of prenatal care as the Secondary Sampling Units (SSUs), and (3) recruitment of participants from selected providers with eligibility criteria based on confirmed pregnancy, age, and residence in the sampled PSU. This approach eliminates the recruitment limitation of requiring participants to reside within predefined geographic segments, and instead bases the geographic eligibility on residing within the PSU. Three counties participated in this feasibility substudy.


A free search engine which primarily accesses the MEDLINE database of references and abstracts on biomedical and life sciences. The United States National Library of Medicine (NLM) at the National Institutes of Health maintains the database.

Recruitment Strategy/Recruitment Schema

A recruitment methodology evaluated for the NCS. The NCS recruitment strategies were: Household based recruitment (Initial Vanguard Study [IVS]), Provider-based Recruitment (PBR), Enhanced Household-based Recruitment (EHBR), Direct Outreach (DO), also known as Two-tiered Recruitment (High Intensity/Low Intensity), and Provider Based Sampling (PBS).

Regional Operations Centers (ROC)

Contract research organizations responsible for participant retention and data collection within the given Study locations divided into four regions (East, Central, South, and West).

Research Materials Distribution Agreement (RMDA)

Agreement with the NICHD governing data and sample use.


The selection of a subset of individuals from a population to estimate selected characteristics of the target population.

Sampling Frame

A listing of the target population from which a sample can be drawn.

Self-administered Questionnaire (SAQ)

A type of questionnaire, either in paper or electronic form, that a respondent completes on his/her own without intervention of the researchers (for example, an interviewer) collecting the data.

Secondary Sampling Units (SSUs)

Units sampled directly within primary sampling units in a multi-stage sample.


In a multi-stage probability sample, primary sampling units (PSUs) are divided into smaller geographic areas called secondary sampling units (SSUs) or segments. In the National Children's Study, the boundaries for these segments correspond to neighborhoods or communities. In Direct Outreach Strategy where three levels of sampling stages exist, tertiary sampling units (TSUs) form the sampled segments. In PBS there were no segments, only PSUs (which are counties).

Study Population

The individuals that are selected from the target population for participation in the Study.

Study Visits

Encounters of Study participants with Study personnel for the purpose of collecting data and/or materials.


Focused clinical research studies that integrate with the Vanguard or Main Study.

T1 First

Designation code in the Initial Vanguard Study for the first trimester visit among enrolled women (equivalent to Pregnancy Visit 1 in the ARS phase).

T3 First

Designation code in the Initial Vanguard Study for the third trimester visit among women who have not previously received a first trimester visit (equivalent to Pregnancy Visit 1 in the ARS phase).

Vanguard Study Locations

The counties (or in sparsely populated areas, groups of contiguous counties) that were selected as primary sampling units in the first stage of sampling. They are the areas from which Study participants were recruited in the Vanguard Study and in which most of the community level data collections occur.

Vanguard Study/Vanguard Phase

The pilot phase of the National Children's Study, designed to study the feasibility, acceptability, and cost of methodological, operational, and logistic activities, recruitment-related activities, and Study visit assessments, for the purpose of informing the Main Study. Refers to all Vanguard Study locations.

Visit Assessment

The various data collections performed at Study visits, including tests, physical measurements, interviews, questionnaires, biospecimens, and environmental samples.



Advisory Committee to the Director Working Group


Alternate Recruitment Substudy


Computer Assisted Personal Interview


Centers for Disease Control and Prevention


Direct Outreach Recruitment


Enhanced Household-based Recruitment


Environmental Protection Agency


High Intensity/Low Intensity data collection


Information Management System


Institutional Review Board


Initial Vanguard Study


National Academy of Sciences


National Children's Study


National Institute of Child Health and Human Development


Office of Management and Budget


Provider-Based Recruitment


Provider-Based Sampling


Personally Identifiable Information


Provider Location


Primary Sampling Unit


Pregnancy Visit


Regional Operations Center


Research Materials Distribution Agreement


Study Centers


Self-administered Questionnaire


Secondary Sampling Unit


Tertiary Sampling Unit


Vanguard Study


Special Supplemental Nutrition Program for Women, Infants, and Children (WIC)