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Cross Sectional Versus Longitudinal Data: An Empirical Comparison of Mean Differences in Academic Growth

Hilton, Thomas L.; Patrick, Cathleen
Publication Year:
Report Number:
ETS Research Bulletin
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Page Count:
Subject/Key Words:
Academic Achievement, Achievement Tests, Comparative Analysis, Cross-Sectional Studies, Data Analysis, Dropouts, Educational Opportunity Survey, Longitudinal Studies, Sampling, Study of Academic Prediction and Growth


Three sources of data for studies of growth (matched longitudinal, unmatched longitudinal, and cross-sectional) are compared using mean achievement test scores collected from 32,000 students tested repeatedly from 1961 to 1967. The principal results were that matched longitudinal data yielded significantly higher means than unmatched longitudinal data, and that a school's dropout rate was highly related to the discrepancy between cross-sectional and matched longitudinal data (r = 85). Seven sources of differences among the three types of data are considered: age differences, cohort differences, time changes, equating errors, retest effects, cohort change effects, and selection effects. Methodological guidelines for future research in studies of growth and change are presented.

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