ERIC Number: ED414283
Record Type: Non-Journal
Publication Date: 1997-May
Reference Count: N/A
Grade Equivalent and IRT Representations of Growth. ACT Research Report Series 97-2.
Schulz, E. Matthew; Nicewander, W. Alan
It has long been a part of psychometric lore that the variance of children's scores on cognitive tests increases with age. This "increasing-variance" phenomenon was first observed on A. Binet's intelligence measures in the early 1900s. An important detail in this matter is the fact that developmental scales based on age or grade have served as the medium for demonstrating the increasing-variance phenomenon. Recently, developmental scales based on item response theory (IRT) have show constant or decreasing variance of measures of achievement with increasing age. This discrepancy is of practical and theoretical importance. Conclusions about the effects of variables on growth in achievement will depend on the metric chosen. In this study, growth in the mean of a latent educational achievement variable is assumed to be a negatively accelerated function of grade; within-grade variance is assumed to be constant across grades, and observed test scores are assumed to follow an IRT model. Under these assumptions, the variance of grade equivalent scores increases markedly. Perspective on this phenomenon is gained by examining longitudinal trends in centimeter and age equivalent measures of height. (Contains 6 figures, 2 tables, and 22 references.) (Author/SLD)
Descriptors: Achievement Gains, Age Differences, Child Development, Children, Cognitive Tests, Grade Equivalent Scores, Item Response Theory, Psychometrics
ACT Research Report Series, P.O. Box 168, Iowa City, IA 52243-0168.
Publication Type: Reports - Evaluative
Education Level: N/A
Authoring Institution: American Coll. Testing Program, Iowa City, IA.