PEDAR: Research Methodology  First-Generation Students in Postsecondary Education: A Look at Their College Transcripts
The Naitonal Education Longitudinal Study of 1988
The NELS:88 Postsecondary Education Transcript Study
Analysis Sample and Weights
Accuracy of Estimates
Data Analysis System
Statistical Procedures
Differences Between Means
Linear Trends
Multivariate Commonality Analysis
Executive Summary
Full Report (PDF)
Executive Summary (PDF)
 Accuracy of Estimates

The statistics in this report are estimates derived from a sample. Two broad categories of error occur in such estimates: sampling and nonsampling errors. Sampling errors occur because observations are made only on samples of students, not entire populations. Nonsampling errors occur not only in sample surveys but also in complete censuses of entire populations. Nonsampling errors can be attributed to a number of sources: inability to obtain complete information about all students in all institutions in the sample (some students or institutions refused to participate, or students participated but answered only certain items); ambiguous definitions; differences in interpreting questions; inability or unwillingness to give correct information; mistakes in recording or coding data; and other errors of collecting, processing, sampling, and imputing missing data. See The National Education Longitudinal Study of 1988: Base-Year to Fourth Follow-Up Data File User’s Manual (Curtin et al. 2002) for details on efforts to minimize such nonsampling errors.

Item Response Rates

From the selected sample of this report, weighted item response rates were calculated for all variables used in this report by dividing the weighted number of valid responses by the weighted population for which the item was applicable. Most items had a high response rate (i.e., above 85 percent). For these variables, it is unlikely that reported differences are biased because of missing data. Two variables that had relatively lower item response rates (below 85 percent) are the highest level of mathematics completed in high school (84 percent) and senior achievement test score in 1992 (80 percent). These two variables were used as row variables in table 1, which shows the distribution of first-generation status according to selected demographic and academic characteristics. However, a bias analysis on these two variables did not find significant differences between first-generation students and the two other groups in terms of the proportion of missing cases on these two variables. Therefore, the statements drawn from these two variables based on table 1 should not be biased due to missing data on these two items.

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