DOI: 10.3886/icpsr21942.v5
title: NICHD Study of Early Child Care and Youth Development: Phase III, 2000-2004 [United States]
title: SECCYD Phase III, 2000-2004
title: Version 5

description: The overall purpose of this study was to examine the influence of
variations in early childcare histories on the psychological
development of infants and toddlers from a variety of family
backgrounds. This general objective was addressed through a
prospective, longitudinal study of the experiences of 1,364 children and
their families, which took into account the
complex interactions among child characteristics and those
of the human and physical environments in which
the children were reared.
Research Goals
The specific research aims were as follows:

Examining the relationship between infants' childcare
arrangements (defined in terms of hours, type, quality, and
stability of care and the age at which the child entered care)
and children's concurrent and long-term development.
Specifically, the study investigated the association between
children's experiences in childcare and their social, emotional,
language, and cognitive development. The social-emotional
assessments included measures of attachment, independence,
compliance, behavior problems, prosocial and antisocial behavior,
and general competence in interacting with peers. Cognitive variables
include general developmental level and problem solving skills. Language
assessments incorporated measures of children's expressive and receptive communicative competence.; 
Examining whether the social ecology of the home
moderates the effects of childcare, i.e., whether children
from different home environments are differentially affected by
similar childcare experiences. The study examined the
moderating effects of parents' values and attitudes,
psychological adjustment and mental health, stress and social
support, child-rearing practices, time use, interactions with the
child, the marital relationship, and family demographics.; 
Examining whether individual differences among children
moderate the effects of infant care on child development. The
study examined the moderating effects of such child
characteristics as age, sex, health, birth order, and
temperament.; 
Identify demographic and family characteristics
associated with families' childcare decisions. The study examined whether
specific childcare arrangements are related to
the parents' social class, marital status, psychological
adjustment and personality, child-rearing values and attitudes,
parenting practices, stress, social support, marital
relationship, and the availability of childcare in the community.; 
Provide a natural history of infant care in the
1990s, and help establish a baseline of data pertaining to the
kinds of care being used by families. Whereas other national
databases, such as those provided by the United States Census Bureau, provide
static estimates of the number of children in different types of
childcare, this network study supplements that knowledge
with longitudinal data on successive enrollments into day care at
various ages, patterns of arrangements used concurrently and over
time, and the stability of arrangements during the first three
years of life. One of the most valuable aspects of the
collaborative study is the opportunity it provides to obtain a
more complete and accurate picture of patterns of infant care
used by families today. Census surveys use only gross categories
of care (e.g., center vs. in-home). In this study, more fine-grained
information regarding the types of centers and home-care
facilities was gathered.; 
Examine the consequences for families of maternal
employment and childcare choices. Family relationships,
parental mental health, family stress, and so on, are not just
inputs to child development or moderators of childcare effects,
they are also outcomes. High-quality childcare may alleviate
family stress and enhance parental adjustment. Low-quality childcare may add to the stress parents experience. Although the main
focus in the study was on the effect of childcare on the child, the
study also examined the effect of childcare on the family.; 
Identify demographic characteristics of childcare
associated with childcare quality. Of interest to policy makers
is another aspect of the study, the investigation of those
regulatory characteristics that predict care of higher quality.
These characteristics included the level and type of caregiver
training, the size of the childcare group, the auspices of the
childcare program (public/private, profit/nonprofit,
independent/chain, employer-sponsored/church-based), whether the
facility was licensed or unlicensed, the level of payment and
fees, and whether the caregiver was a relative of the family.; 
Data File Organization
504 data files were compiled for this study and are organized into 4 main groups:

Analytical Data Sets (ADS) -- The raw data were examined and composites defined by small groups of individual principal investigators according to the demographic, family, childcare, and child outcome content of the data. The psychometric and distributional qualities of the variables along with site differences were examined. A set of variables that was psychometrically and distributionally acceptable to be used in analytic analyses was designed to test the study hypotheses. These data files comprise Parts 1-49 of the study data material.; 
Supplemental Data Sets -- New and revised analysis variables as well as across-time mean scores and primary composites were produced as a supplement to the original Analytical Data Sets. These data files comprise Parts 50-55 of the study data material.; 
Raw Census-Related Data Sets -- Files were produced using geocoded addresses for survey respondents to match block group level data from the 1990 and 2000 Censuses for investigators to create additional measures of interest from the geocoded addresses. These data files comprise Parts 56-58 of the study data material.; 
Raw Data Sets -- The raw data were made available and comprise Parts 59-505 of the study data material.; 
Training Workshop
A three-day summer training workshop on the SECCYD was put on by NICHD at the Inter-University Consortium for Political and Social Research in Ann Arbor, Michigan in 2010. The binder from that workshop, which includes the Powerpoint slides used during presentations, are freely available to the public as part of the study documentation.
description: To examine the influence of variations in early childcare histories on the psychological development of infants and toddlers from a variety of family backgrounds.
description: The SECCYD is a multi-site, prospective, longitudinal study of the experiences of 1,364 children and their families. Respondents were sampled from a catchment of some 6,189 children. Children's development was assessed via trained observers, interviewers, questionnaires, and direct testing. Measures were taken on many facets of children's development, such as social, emotional, intellectual, and language development, behavioral problems and adjustment, and physical health.
During Phase III of the study, data was collected from the study children, the study children's families, after-school caregivers, and teachers from the second through sixth grades. Data also were collected from friends of the study children and from their families and teachers at fourth and sixth grades. Prior to the start of formal schooling, data were collected on an age-based chronological schedule. With the onset of formal schooling, data were collected on a year-in-school basis. As a result, children who entered school in fall 1996, who accounted for 85 percent of the available sample, became Wave 1. The remaining 15 percent of the sample, who entered school in fall 1997, became Wave 2. However, annual Health and Physical Development Assessments (HPDA), which began when the study children were nine-and-a-half years old, continue on an age-related basis.
description: The 49 Analytical Data Sets (ADS) contain composite variables created from the raw data by Quantitative Systems Laboratory (QSL) at Vanderbilt University, to be psychometrically and distributionally acceptable for analytical analysis of the study hypotheses. The 6 Supplemental Data Sets were produced by Research Triangle Institute (RTI) and contain new and revised analysis variables, across-time mean scores, and primary composites. The 3 Raw Census Related Data Sets were produced using geocoded addresses for survey respondents to match block group- level data from the 1990 and 2000 Censuses, for investigators to create additional measures of interest from the geocoded addresses. The CENS1990 raw dataset contains 947 block group variables for 2,720 address records with start dates before January 1, 1996, for 1295 study children. The CENS2000 raw dataset contains 1,423 block group variables for 2,891 address records with end dates after December 31, 1995, for 1,159 study children. The 447 Raw Data Sets contain the direct item-level data collected per instrument.
description: ICPSR data undergo a confidentiality review and are altered when necessary to limit the risk of 
				disclosure. ICPSR also routinely creates ready-to-go data files along with setups in the major 
				statistical software formats as well as standard codebooks to accompany the data. In addition to 
				these procedures, ICPSR performed the following processing steps for this data collection:
			   		Created variable labels and/or value labels.; Checked for undocumented or out-of-range codes..
description: Presence of Common Scales: 
					 Student-Teacher Relationship Scale: Short Form;  Social Skills Rating Scale;  Middle Childhood H.O.M.E;  Child Behavior Checklist;  Child-Parent Relationship Scale: Short Form;  Child-Caregiver Rel. Scale: Short Form;  Girls' Pubertal Development Scale;  Boys' Pubertal Development Scale;  Woodcock-Johnson Cognitive Sub-tests;  Woodcock-Johnson Achievement Sub-tests;  Teacher Self Efficacy Scale;  Wechsler Abbreviated Scale of Intelligence (WASI);  Peabody Picture Vocabulary Test - III (PPVT);  H.O.M.E Inventory Scoring;  Multi Ethnic Identity Measure (MEIM);  Multidimensional Inventory of Black Identity (MIBI);  Woodcock Johnson-Revised Achievement Scale;  Woodcock Johnson-Revised Cognitive Scale;  COS Structural Scales;  COS Behavior Scales;  COS Qualitative Scales;
description: Response Rates: 
					During Phase I of the study (1991-1994), a cohort of 1,364 children and their families were recruited at 1 month of age and studied intensively through age 3. During Phase III of the study (2000-2004), a cohort of over 1,100 of the enrolled children and families were followed through sixth grade.
description: Datasets: 
					
						DS0: Study-Level Files
						DS1: ADS-ASCAREG2
						DS2: ADS-COUTG2
						DS3: ADS-DEMOG2
						DS4: ADS-SCHG2
						DS5: ADS-TCHRG2
						DS6: ADS-ASCAREG3
						DS7: ADS-ASCGG3
						DS8: ADS-COUTG3
						DS9: ADS-DEMOG3
						DS10: ADS-FAMG3
						DS11: ADS-HPAG3
						DS12: ADS-SCHG3
						DS13: ADS-TCHRG3
						DS14: ADS-ASCAREG4
						DS15: ADS-ASCGG4
						DS16: ADS-COUTG4
						DS17: ADS-DEMOG4
						DS18: ADS-FAMG4
						DS19: ADS-FRDEMOG4
						DS20: ADS-FRFAMG4
						DS21: ADS-FROUTG4
						DS22: ADS-FRSCHG4
						DS23: ADS-FRTCHRG4
						DS24: ADS-HPAG4
						DS25: ADS-SCHG4
						DS26: ADS-TCHRG4
						DS27: ADS-ASCAREG5
						DS28: ADS-ASCGG5
						DS29: ADS-COUTG5
						DS30: ADS-DEMOG5
						DS31: ADS-FAMG5
						DS32: ADS-HPAG5
						DS33: ADS-SCHG5
						DS34: ADS-TCHRG5
						DS35: ADS-ASCAREG6
						DS36: ADS-COUTG6
						DS37: ADS-DEMOG6
						DS38: ADS-FAMG6
						DS39: ADS-FRDEMOG6
						DS40: ADS-FRFAMG6
						DS41: ADS-FROUTG6
						DS42: ADS-FRSCHG6
						DS43: ADS-FRTCHRG6
						DS44: ADS-HPAG6
						DS45: ADS-SCHG6
						DS46: ADS-TCHRG6
						DS47: ADS-BMIHIST
						DS48: ADS-RESHIST
						DS49: ADS-SCHHIST
						DS50: Supplemental-FPA07G3B
						DS51: Supplemental-FPA07G5B
						DS52: Supplemental-FPA07G6B
						DS53: Supplemental-REVPAMG3
						DS54: Supplemental-REVPAMG5
						DS55: Supplemental-REVPAMG6
						DS56: Census-ACTV1MX5
						DS57: Census-CENS1990
						DS58: Census-CENS2000
						DS59: RAW-AS2FS_A
						DS60: RAW-FG2FA
						DS61: RAW-FG2SA
						DS62: RAW-FPH2C
						DS63: RAW-FSV10G2
						DS64: RAW-FSV11G2
						DS65: RAW-FSV12G2
						DS66: RAW-FSV13G2
						DS67: RAW-FSV14G2
						DS68: RAW-FSV4G2_A
						DS69: RAW-FSV5G2
						DS70: RAW-FSV6G2_A
						DS71: RAW-FSV7G2
						DS72: RAW-FSV8G2_A
						DS73: RAW-FSV9G2
						DS74: RAW-HH2FS_A
						DS75: RAW-FAC01G3A
						DS76: RAW-FAP01G3B
						DS77: RAW-FAS01G3
						DS78: RAW-FAS02G3A
						DS79: RAW-FAS03G3A
						DS80: RAW-FAS04G3
						DS81: RAW-FAS05G3
						DS82: RAW-FAS06G3
						DS83: RAW-FG3FA
						DS84: RAW-FHV01G3
						DS85: RAW-FHV04G3
						DS86: RAW-FHV05G3
						DS87: RAW-FHV06G3A
						DS88: RAW-FHV08G3
						DS89: RAW-FHV09G3
						DS90: RAW-FHV10G3
						DS91: RAW-FHV11G3A
						DS92: RAW-FHV12G3A
						DS93: RAW-FHV13G3
						DS94: RAW-FHV14G3A
						DS95: RAW-FHV15G3
						DS96: RAW-FHV16G3
						DS97: RAW-FHV17G3
						DS98: RAW-FHV18G3
						DS99: RAW-FHV19G3
						DS100: RAW-FHV20G3
						DS101: RAW-FHV21G3
						DS102: RAW-FHV22G3
						DS103: RAW-FHV23G3
						DS104: RAW-FHV24G3
						DS105: RAW-FHV25G3
						DS106: RAW-FHV26G3A
						DS107: RAW-FHV27G3
						DS108: RAW-FHV28G3A
						DS109: RAW-FHV29G3
						DS110: RAW-FHV30G3
						DS111: RAW-FHV31G3
						DS112: RAW-FHV32G3
						DS113: RAW-FHV33G3
						DS114: RAW-FHV34G3
						DS115: RAW-FHV35G3
						DS116: RAW-FHV36G3
						DS117: RAW-FHV37G3
						DS118: RAW-FHV38G3
						DS119: RAW-FHV39G3
						DS120: RAW-FHV40G3
						DS121: RAW-FHV41G3A
						DS122: RAW-FHV42G3A
						DS123: RAW-FLV01G3A
						DS124: RAW-FLV02G3A
						DS125: RAW-FLV04G3
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						DS128: RAW-FLV07G3
						DS129: RAW-FLV08G3
						DS130: RAW-FLV11G3
						DS131: RAW-FLV13G3A
						DS132: RAW-FLV14G3A
						DS133: RAW-FLV15G3
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						DS136: RAW-FLV18G3
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						DS140: RAW-FLV22G3
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						DS144: RAW-FLV26G3
						DS145: RAW-FLV27G3
						DS146: RAW-FLV28G3
						DS147: RAW-FPA01G3
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						DS150: RAW-FPA07G3A
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						DS160: RAW-FSV11G3A
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						DS166: RAW-FSV17G3A
						DS167: RAW-FSV19G3
						DS168: RAW-FSV20G3
						DS169: RAW-HH3F_A
						DS170: RAW-JB3F_A
						DS171: RAW-FAC01G4A
						DS172: RAW-FAP01G4A
						DS173: RAW-FAS01G4
						DS174: RAW-FAS02G4A
						DS175: RAW-FAS03G4A
						DS176: RAW-FAS04G4
						DS177: RAW-FAS05G4
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						DS179: RAW-FCPTG4
						DS180: RAW-FG4FA
						DS181: RAW-FLV01G4
						DS182: RAW-FLV05G4
						DS183: RAW-FLV06G4B
						DS184: RAW-FLV07G4A
						DS185: RAW-FLV08G4
						DS186: RAW-FLV09G4A
						DS187: RAW-FLV10G4
						DS188: RAW-FLV11G4A
						DS189: RAW-FLV12G4
						DS190: RAW-FLV13G4
						DS191: RAW-FLV14G4
						DS192: RAW-FLV15G4
						DS193: RAW-FLV16G4
						DS194: RAW-FLV17G4
						DS195: RAW-FLV18G4
						DS196: RAW-FLV19G4
						DS197: RAW-FLV20G4
						DS198: RAW-FLV21G4
						DS199: RAW-FLV22G4A
						DS200: RAW-FLV23G4
						DS201: RAW-FLV24G4A
						DS202: RAW-FLV25G4
						DS203: RAW-FLV26G4
						DS204: RAW-FLV27G4
						DS205: RAW-FLV28G4
						DS206: RAW-FLV29G4
						DS207: RAW-FLV2FG4
						DS208: RAW-FLV2SG4
						DS209: RAW-FLV30G4
						DS210: RAW-FLV31G4
						DS211: RAW-FLV32G4
						DS212: RAW-FLV33G4A
						DS213: RAW-FLV34G4
						DS214: RAW-FLV35G4
						DS215: RAW-FLV36G4
						DS216: RAW-FLV37G4
						DS217: RAW-FLV38G4
						DS218: RAW-FLV39G4
						DS219: RAW-FLV3FG4
						DS220: RAW-FLV3SG4
						DS221: RAW-FLV4FG4
						DS222: RAW-FLV4SG4
						DS223: RAW-FPD01G4
						DS224: RAW-FPD02G4
						DS225: RAW-FPD03G4
						DS226: RAW-FPD04G4
						DS227: RAW-FPD05G4
						DS228: RAW-FPD06G4
						DS229: RAW-FPD08G4
						DS230: RAW-FPD11G4
						DS231: RAW-FSA01G4
						DS232: RAW-FSF24G4
						DS233: RAW-FSV04G4
						DS234: RAW-FSV05G4
						DS235: RAW-FSV06G4
						DS236: RAW-FSV07G4
						DS237: RAW-FSV08G4A
						DS238: RAW-FSV09G4
						DS239: RAW-FSV10G4A
						DS240: RAW-FSV11G4
						DS241: RAW-FSV12G4
						DS242: RAW-FSV13G4
						DS243: RAW-FSV14G4
						DS244: RAW-FSV15G4
						DS245: RAW-FSV16G4A
						DS246: RAW-FSV17G4
						DS247: RAW-FSV18G4A
						DS248: RAW-FSV19G4
						DS249: RAW-FSV20G4
						DS250: RAW-FSV21G4
						DS251: RAW-FSV22G4A
						DS252: RAW-FSV23G4A
						DS253: RAW-FSV24G4
						DS254: RAW-FSV25G4
						DS255: RAW-HH4F_A
						DS256: RAW-JB4F_A
						DS257: RAW-FAC01G5A
						DS258: RAW-FAP01G5A
						DS259: RAW-FAS01G5
						DS260: RAW-FAS02G5A
						DS261: RAW-FAS03G5A
						DS262: RAW-FAS04G5
						DS263: RAW-FAS05G5
						DS264: RAW-FAS06G5
						DS265: RAW-FG5SA
						DS266: RAW-FHV01G5
						DS267: RAW-FHV02G5
						DS268: RAW-FHV03G5
						DS269: RAW-FHV04G5
						DS270: RAW-FHV05G5
						DS271: RAW-FHV06G5
						DS272: RAW-FHV07G5
						DS273: RAW-FHV08G5
						DS274: RAW-FHV09G5
						DS275: RAW-FHV10G5
						DS276: RAW-FHV11G5A
						DS277: RAW-FHV12G5
						DS278: RAW-FHV13G5
						DS279: RAW-FHV14G5
						DS280: RAW-FHV15G5A
						DS281: RAW-FHV16G5
						DS282: RAW-FHV17G5
						DS283: RAW-FHV18G5A
						DS284: RAW-FHV19G5
						DS285: RAW-FHV20G5
						DS286: RAW-FHV21G5
						DS287: RAW-FHV22G5
						DS288: RAW-FHV23G5
						DS289: RAW-FHV24G5
						DS290: RAW-FHV25G5
						DS291: RAW-FHV26G5A
						DS292: RAW-FHV27G5
						DS293: RAW-FHV28G5
						DS294: RAW-FHV29G5A
						DS295: RAW-FHV30G5
						DS296: RAW-FHV31G5
						DS297: RAW-FHV32G5
						DS298: RAW-FHV33G5
						DS299: RAW-FHV34G5
						DS300: RAW-FHV35G5
						DS301: RAW-FHV36G5
						DS302: RAW-FHV37G5
						DS303: RAW-FHV38G5
						DS304: RAW-FHV39G5
						DS305: RAW-FHV40G5
						DS306: RAW-FHV41G5
						DS307: RAW-FHV42G5
						DS308: RAW-FHV43G5A
						DS309: RAW-FHV44G5A
						DS310: RAW-FLV01G5
						DS311: RAW-FLV02G5A
						DS312: RAW-FLV03G5A
						DS313: RAW-FLV04G5C
						DS314: RAW-FLV05G5
						DS315: RAW-FLV06G5A
						DS316: RAW-FLV07G5B
						DS317: RAW-FLV08G5
						DS318: RAW-FLV09G5
						DS319: RAW-FLV10G5
						DS320: RAW-FLV11G5
						DS321: RAW-FLV12G5
						DS322: RAW-FLV13G5
						DS323: RAW-FLV14G5
						DS324: RAW-FLV15G5
						DS325: RAW-FLV16G5
						DS326: RAW-FLV17G5
						DS327: RAW-FLV18G5A
						DS328: RAW-FLV20G5
						DS329: RAW-FLV21G5
						DS330: RAW-FLV22G5
						DS331: RAW-FLV23G5
						DS332: RAW-FLV24G5
						DS333: RAW-FLV25G5
						DS334: RAW-FLV26G5
						DS335: RAW-FLV27G5
						DS336: RAW-FLV28G5
						DS337: RAW-FLV29G5
						DS338: RAW-FLV30G5
						DS339: RAW-FLV31G5
						DS340: RAW-FLV32G5
						DS341: RAW-FLV33G5
						DS342: RAW-FLV34G5
						DS343: RAW-FLV35G5
						DS344: RAW-FLV36G5
						DS345: RAW-FLV37G5A
						DS346: RAW-FLV38G5A
						DS347: RAW-FPA01G5
						DS348: RAW-FPA03G5
						DS349: RAW-FPA06G5
						DS350: RAW-FPA07G5A
						DS351: RAW-FPD01G5
						DS352: RAW-FPD02G5
						DS353: RAW-FPD03G5
						DS354: RAW-FPD04G5
						DS355: RAW-FPD05G5
						DS356: RAW-FPD06G5
						DS357: RAW-FPD08G5
						DS358: RAW-FPD11G5
						DS359: RAW-FSA01G5
						DS360: RAW-FSV01G5A
						DS361: RAW-FSV02G5
						DS362: RAW-FSV03G5
						DS363: RAW-FSV05G5
						DS364: RAW-FSV06G5
						DS365: RAW-FSV07G5
						DS366: RAW-FSV08G5
						DS367: RAW-FSV09G5
						DS368: RAW-FSV10G5
						DS369: RAW-FSV11G5A
						DS370: RAW-FSV12G5
						DS371: RAW-FSV13G5A
						DS372: RAW-FSV14G5
						DS373: RAW-FSV15G5
						DS374: RAW-FSV16G5
						DS375: RAW-FSV17G5A
						DS376: RAW-FSV18G5A
						DS377: RAW-FSV20G5
						DS378: RAW-FSV21G5
						DS379: RAW-HH5S_A
						DS380: RAW-JB5S_A
						DS381: RAW-FLV01G6
						DS382: RAW-FLV02G6
						DS383: RAW-FLV03G6
						DS384: RAW-FLV04G6
						DS385: RAW-FLV05G6A
						DS386: RAW-FLV07G6
						DS387: RAW-FLV07G6F
						DS388: RAW-FLV08G6
						DS389: RAW-FLV08G6F
						DS390: RAW-FLV09G6
						DS391: RAW-FLV09G6F
						DS392: RAW-FLV10G6
						DS393: RAW-FLV10G6F
						DS394: RAW-FLV11G6
						DS395: RAW-FLV11G6F
						DS396: RAW-FLV12G6
						DS397: RAW-FLV12G6F
						DS398: RAW-FLV13G6
						DS399: RAW-FLV14G6
						DS400: RAW-FLV14G6F
						DS401: RAW-FLV15G6
						DS402: RAW-FLV15G6F
						DS403: RAW-FLV16G6
						DS404: RAW-FLV16G6F
						DS405: RAW-FLV17G6
						DS406: RAW-FLV17G6F
						DS407: RAW-FLV18G6
						DS408: RAW-FLV19G6
						DS409: RAW-FLV20G6
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						DS496: RAW-NCES9603
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						DS504: RAW-FPH3R
						DS505: RAW-FG6FA
description: NICHD Study of Early Child Care and Youth Development (SECCYD) Series
description: computer-assisted personal interview (CAPI)
description: computer-assisted telephone interview (CATI)
description: coded on-site observation
description: cognitive assessment test
description: face-to-face interview
description: mail questionnaire
description: self-enumerated questionnaire
description: on-site questionnaire
description: telephone interview
description: Full-term, healthy newborns of mothers giving birth in hospitals at 10 locations throughout the United States during designated 24-hour periods between January and November 1991.
description: Participants were selected in accordance with a conditionally random sampling plan, which was designed to ensure that the recruited families (a) included mothers who planned to work or to go to school full-time (60 percent) or part-time (20 percent) in the child's first year, as well as some who planned to say at home with the child (20 percent), and (b) reflected the demographic diversity (economic, educational, and ethnic) of the sites. Both two-parent and single-parent families were included. The major exclusionary criteria used were (a) mothers younger than 18 years of age at the time of the child's birth, (b) families who did not anticipate remaining in the catchment area for at least 3 years, (c) children with obvious disabilities at birth or who remained in the hospital more than 7 days postpartum, and (d) mothers not sufficiently conversant in English. Analyses have indicated that the data do reflect the natural distributions of these factors in the catchment. Therefore, inferences from this data can be made directly to the catchment without back-weighting for the sampling factors. In addition, analyses have shown that the NICHD data reflect to large degree the natural distributions of certain factors measured in the 1990 Census data. However, the NICHD data are not representative in the statistical sense, and therefore inference to the nation as a whole is not possible. Comparisons to other data bases, national or otherwise, should be made with extreme caution.