Title: Self efficacy for fruit, vegetable and water intakes: expanded and abbreviated scales from item response modeling analyses Authors
|Baranowski, Tom -|
|Watson, Kathleen -|
|Bachman, Christine -|
|Baranowski, Janice -|
|Cullen, Karen -|
|Siega Riz, Anna-Maria -|
Submitted to: International Journal of Behavioral Nutrition and Physical Activity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 29, 2010
Publication Date: March 29, 2010
Repository URL: http://www.ijbnpa.org/content/7/1/25
Citation: Baranowski, T., Watson, K., Bachman, C., Baranowski, J., Cullen, K., Thompson, D.J., Siega Riz, A. 2010. Self efficacy for fruit, vegetable and water intakes: expanded and abbreviated scales from item response modeling analyses. International Journal of Behavioral Nutrition and Physical Activity. 7:25. Interpretive Summary: High quality measures are needed of key psychosocial constructs, both to understand influences on behavior and to assess how/whether interventions impact behaviors. Our previous IRM (Item Response Modeling) analyses of a measure of fruit and vegetable self efficacy indicated that the distribution of items was highly restricted along the latent variable of difficulty. As a result, we initiated a theory specified process to better distribute items along the latent variable, and collected data on 714 children. These analyses indicated that despite our best efforts, we could not further distribute items across the latent variable. More drastic efforts are needed to refine items to further spread them along the latent variable.
Technical Abstract: Our objective was to improve an existing measure of fruit and vegetable intake self efficacy, by including items that varied on levels of difficulty, and testing a corresponding measure of water intake self efficacy. A cross sectional assessment was used. Items were modified to have easy, moderate, and difficult levels of self efficacy. Classical test theory and item response modeling were applied. One middle school at each of seven participating sites (Houston TX, Irvine CA, Philadelphia PA, Pittsburg PA, Portland OR, rural NC, and San Antonio TX), were utilized to evaluate 714 6th grade students participated in the study. Our results showed that adding items to reflect level (low, medium, high) of self efficacy, for fruit and vegetable intake achieved scale reliability and validity comparable to existing scales, but the distribution of items across the latent variable did not improve. Selecting items from among clusters of items at similar levels of difficulty along the latent variable resulted in an abbreviated scale with psychometric characteristics comparable to the full scale, except for reliability. We concluded that the abbreviated scale could reduce participant burden. Additional research is necessary to generate items that better distribute across the latent variable. Additional items may need to tap confidence in overcoming more diverse barriers to dietary intake.