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

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.

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.

Data were collected as part of a larger study investigating factors influencing consumption of fruit, vegetables, and cereal foods.

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.

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.

Results of this study provide preliminary evidence for the utility of the scale to guide development and monitoring of community programs and therapeutic interventions.