skip to main content skip to footer

An Evaluation of the Single-Group Growth Model as an Alternative to Common-Item Equating SGGM

Wei, Youhua; Morgan, Rick
Publication Year:
Report Number:
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Test Repeater, Single-Group Growth Model (SGGM), Linking, Common Item Equating


Then the repeaters taking both the current and previous administrations are identified, and their scale score distribution on the current form is estimated based on their previous scale score distribution and the estimated conditional distribution. Finally, a single-group equipercentile equating is performed between the current-form repeaters' observed raw score distribution and their estimated scale score distribution to obtain the raw-to-scale score conversion. This study evaluated the SGGM scaling performance using the common-item equating results for a language test as the criterion. The study found that the raw-to-scale conversions based on SGGM scaling differed from those based on common-item equating. However, the SGGM scaling results did not show a systematic bias in either the average or the variability of examinees' scale scores.

Read More