Purpose: An audience-centered approach was used to develop valid and reliable scales to measure adult self-efficacy to eat fruit and vegetables.
Design: Cross-sectional survey of a national population.
Setting: New Zealand.
Subjects: A sample of 350 adults ages 25 to 60 years was randomly selected from a nationally representative sampling frame. Overall, 231 questionnaires were returned, producing a 72% response rate. The mean age of subjects was 42.7years; 58% were female; 80% were of European descent; 11% were indigenous Maori.
Measures: The 76-item, self-administered questionnaire collected data on demographics, fruit and vegetable intakes, stages of change, decisional balance, and self-efficacy (24 items).
Analysis: Principal components analysis with oblimin rotation was performed.
Results: Principal components analysis yielded three distinct and reliable scales for self-efficacy to eat "vegetables," "fruit," and "fruit and vegetables" (Cronbach alpha = .80, .85, and .73, respectively). These scales were correlated, but only the "vegetable" scale was positively correlated with the "fruit and vegetable" scale (Kendall tau r = 0.30, -0.26 [fruit, "fruit and vegetables"], -0.38 [fruit, vegetable]). As predicted, self-efficacy was associated with intake (r = 0.30 [fruit], 0.34 [vegetables]).
Conclusion: Assuming the factor structure is confirmed in independent samples, these brief psychometrically sound scales may be used to assess adult self-efficacy to eat fruit and to eat vegetables (separately) but not self-efficacy to eat "fruit and vegetables."