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Measuring pretest-posttest change with a Rasch Rating Scale Model.

E W Wolfe¹, C W Chiu

¹University of Florida, Gainesville 32611, USA. ewolfe@ufl.edu

Journal of Outcome Measurement

|April 16, 1999

Summary

This study introduces a method to separate genuine changes in individuals from shifts in how they interpret survey questions or use rating scales over time. It helps ensure accurate measurement by establishing a consistent reference point.

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Area of Science:

Psychometrics
Quantitative Psychology
Measurement Theory

Background:

Longitudinal studies face challenges distinguishing individual change from measurement context shifts.
Changes in item interpretation or rating scale use can confound results.
Accurate assessment of change requires separating person-based from measurement-based variance.

Purpose of the Study:

To present a method for disentangling changes in persons from changes in measurement interpretation over time.
To provide a practical framework for analyzing longitudinal data from Likert-type questionnaires.
To illustrate the application of anchoring strategies for stable measurement.

Main Methods:

Utilizes anchoring strategies to establish a common frame of reference.
Applies the FACETS software for detailed implementation.
Develops a procedure to differentiate between person-level and item-level changes.

Main Results:

The described method effectively separates genuine individual changes from alterations in measurement interpretation.
Anchoring strategies create a stable reference point for longitudinal comparisons.
FACETS provides a robust platform for implementing this disentanglement procedure.

Conclusions:

The proposed method enhances the validity of longitudinal research by isolating true person change.
Accurate measurement over time is achievable through careful attention to the measurement context.
This approach offers a valuable tool for researchers using repeated measures.

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