Chapter 2
Considerations in developing vertical scales for language
tests
This chapter provides a framework for building vertical
scales, for language assessments in general and for the
TOEFL® Family of Assessments in particular. Topics
covered include aspects of vertical scale design (growth definitions,
vertical articulation, data collection), statistical methods for
vertical linking, and evaluation and maintenance of the resulting
vertical scale. Also discussed are challenges associated with vertical
scaling, as noted in the research literature, in general and as pertains
to language proficiency assessments.
Article outline
- Introduction
- Vertical scale design
- Growth definitions
- Vertical articulation
- Data collection design
- Statistical methods for vertical linking
- Hieronymus scaling
- Thurstone scaling
- IRT scaling
- IRT scaling Decision 1: Choice of model
- IRT scaling Decision 2: Separate vs concurrent
calibration
- IRT scaling Decision 3: Scores
- Evaluation of a vertical scale
- Maintenance of the vertical scale
- Challenges with vertical scaling
- Conclusion
-
References