An Examination of the Assumption That the Equating of Parallel Forms Is Population-Independent

Author(s):
Angoff, William H.; Cowell, William R.
Publication Year:
1985
Report Number:
RR-85-22
GREB-83-12P
Source:
Journal of Educational Measurement, 1986, 23(4), 327-345.
Document Type:
Subject/Key Words:
Equated scores physical sciences statistical analysis test theory testing problems

Abstract

Linear and equipercentile conversions were developed relating Forms 3DGR1 and 3DGR3 of the homogeneous GRE quantitative test and the specially constituted heterogeneous GRE verbal-plus-quantitative test, using randomly equivalent populations of about 13,500 cases taking each form, drawn from the entire candidate group tested in the regular October 1981 administration of the Graduate Record Examinations. Conversions for the samples drawn from the Physical Science subpopulation differed significantly from that of the total population. When the appropriate adjustments for the moments were made, it was found that the Physical Sciences conversions fell clearly in line for the homogeneous GRE quantitative test, but not quite so clearly for the heterogeneous GRE verbal-plus-quantitative test. The conversions for all other subpopulation samples were acceptably within range of the population conversion. It was concluded that the assumption of population- independence for equating is supportable for homogeneous tests but, because of evidence of nonparallelism between the two forms, the assumption is not as clearly established by the data of this study for heterogeneous tests.

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