As in any very large survey, the sample that provided data for the National Longitudinal Study of the High School Class of 1972 (NLS) differed from the random sample of the study design because of nonresponse from 226 of the 1,200 schools in the primary sample, and a small amount of other missing data. Part A of this report, briefly describes the design of the sample, including provisions for selecting alternate schools for those that declined to participate, the detailed stratification plan, and an overview of the project. Part B presents a synopsis of the findings which indicated that the majority of the estimated totals for the base year survey were significantly biased by the lack of data from the nonresponding schools. This conclusion is based on data from the first follow-up survey of 1973 which reduced the nonresponse rate to a minimal two percent. Part C describes the methodology and assumptions of the statistical procedures used in estimating the bias resulting from nonresponse. Part D tabulates the statistical results of this study. The appendix provides an alternative methodology for estimating bias in the base year statistics. (CTM)