Self-efficacy and consumption of fruit and vegetables: validation of a summated scale.

PURPOSE: To develop and validate a scale to assess self-efficacy for increasing fruit and vegetable consumption, and to assess the ability of the scale to discriminate individuals at different stages of readiness to change.
METHODS: Data were collected using a combination of self-administered mail questionnaires and phone interviews from a sample of 1200 Chinese Singaporeans randomly selected from residential phone listings. Principal-components analysis was conducted with half the sample, and model fit was measured using structural modeling procedures on the other half. Analyses of variance were used to determine whether self-efficacy differed across the stages of change.
SETTING: Data were collected as part of a larger study investigating factors influencing consumption of fruit, vegetables, and cereal foods. MEASURES: Fruit and vegetable intake was measured using a validated seven-item food frequency questionnaire. Subjects were assigned to stages using a phone-administered staging algorithm. Self-efficacy items were scored on a five-point Likert scale from very confident to not at all confident.
RESULTS: Principal-components analysis revealed a two-factor structure that was highly stable across two split-half samples and gender, and accounted for 57% of the variance in self-efficacy. The two factors demonstrated good internal consistency (Cronbach's alpha = 0.77 and 0.89), with loadings ranging from 0.59 to 0.86 (mean = 0.70). Confirmatory factor analysis demonstrated good model fit (goodness-of-fit index = 0.99), with all parameters significant. Scores on the scale were significantly higher among subjects assigned to maintenance than among those assigned to precontemplation, contemplation, and preparation.
CONCLUSIONS: Results of this study provide preliminary evidence for the utility of the scale to guide development and monitoring of community programs and therapeutic interventions.