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Does participation in an intervention affect responses on self-report questionnaires?
Tom Baranowski1, Diane D Allen, Louise C Mâsse
1Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA. tbaranow@bcm.tmc.edu
Health Education Research
|October 25, 2006
Summary
Differential item functioning (DIF) analysis in a dietary intervention trial revealed more item interpretation changes for fruit and vegetable frequency than for preferences or self-efficacy. Further research is needed to confirm these findings.
Area of Science:
- Psychometrics
- Behavioral Science
- Nutrition Research
Background:
- Self-report questionnaires are susceptible to response bias due to intervention participation or repeated exposure to measurement instruments.
- Differential item functioning (DIF) analysis offers a method to detect potential changes in item interpretation across groups or over time.
Purpose of the Study:
- To investigate differential item functioning (DIF) in a dietary intervention trial among Boy Scouts.
- To assess changes in the interpretation of items related to fruit and vegetable (FV) consumption frequency, preferences, and self-efficacy.
Main Methods:
- Utilized item response modeling to conduct DIF analysis on data from a dietary change intervention trial.
- Compared treatment versus control groups at post-intervention assessment for DIF.
- Analyzed changes within the control group between Time 1 and Time 2 assessments for DIF.
Main Results:
- A higher percentage of items showed treatment-control group DIF at post-intervention for FV frequency compared to FV preferences or self-efficacy.
- One item each for FV frequency, preference, and self-efficacy demonstrated DIF within the control group from Time 1 to Time 2.
Conclusions:
- The study identified potential differential item functioning (DIF) in a dietary intervention context, particularly for fruit and vegetable frequency measures.
- Further research is required to determine if observed DIFs represent genuine changes in constructs or alterations in item interpretation by participants.
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