Submitted to: Meeting Abstract
Publication Type: Abstract only
Publication Acceptance Date: 7/13/2006
Publication Date: 7/13/2006
Citation: Baranowski, T., Wilson, M., Allen, D., Masse, L. 2006. Differential item functioning at post assessment between treatment and control groups from an increase in knowledge [abstract]. Fifth Conference of the International Society of Behavioral Nutrition and Physical Activity, July 13-16, 2006, Boston, Massachusetts. p. 74. Interpretive Summary:
Technical Abstract: There has been some concern that participation in an intervention and exposure to a measurement instrument can distort subsequent responses to a questionnaire, thereby biasing results. Differential Item Functioning (DIF) analysis with Item Response Modeling (IRM) can test these effects by testing for differences in item location between groups. The DIF for treatment versus control group differences in a control group were tested with measures of fruit and vegetable (FV) frequency of consumption, preference and self efficacy in a dietary change intervention trial with Boy Scouts. Treatment-control group DIF at post-intervention assessment was detected for FV frequency, but not preference or self efficacy. Time 1 to time 2 DIF in the control group was detected for all three scales. Further research will need to clarify whether the obtained DIFs reflected true changes in the items or some reinterpretation of items by participants on a constant underlying scale.