(pdf - 215kb)The Current Study
The ECLS-B is a nationally representative sample of the nearly 4 million children born in the United States in the year 2001.2 During the first wave of the study, 10,688 parents provided information and 10,221 children were directly assessed. The parent weight (WIR0) is the weight used to produce all estimates in this report. Only those cases with completed parent interviews are included in this weight.3 Since the sampled children were born between January and December 2001, baseline data were collected on a rolling basis between the fall of 2001 and the fall of 2002.
The ECLS-B was designed to collect information from children and their families for the first time when the children were about 9 months of age (i.e., 8 to 10 months). However, information was collected from a few children as young as 6 months and as old as 22 months. The term "9 months" is used throughout this document to refer to the data collection that took place between fall 2001 and fall 2002, at which time most of the sampled children were about 9 months of age (72 percent of the population was 8 to 10 months of age) (table 1). For ease of reporting, this E.D. TAB uses the term "about 9 months of age" to refer to the entire population of children in the study. Four additional waves of data collection are planned for when the children are 2-year-olds, preschool-aged (e.g., age 4), and then when they are in kindergarten and first grade.
Overall, 74.1 percent of the children in the sample participated in the study. For more information on response rates, data reliability, and test procedures, please refer to appendix A.
Comparisons made in the text were tested for statistical significance to ensure that the differences were larger than might be expected due to sampling variation. All differences reported are significant at the p<.05 level.4
2 Sampling was based on occurence of birth as listed on the birth certificate. Sampled children subsequently identified by the state registrars as having died or who had been adopted near or at the time of birth were excluded. However, data were collected when the children were 9 months of age, so there are some cases with adoptive parents.3 More parents were assessed than children due to a variety of reasons, such as parents refused child assessment, child's availability at time of assessment (e.g., napping).
4 Other publications prepared by the National Center for Education Statistics based on the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (a sister study to the ECLS-B) have employed the use of effect sizes to aid in the interpretation of statistically significant differences. These tabulations are meant to be a preliminary summative examination of the data and do not use effect size differences as a guide.
