Betrouwbaarheid en validiteit van een fruit en groente self-efficacy meetinstrument voor Nederlandse middelbare scholieren

Objective: One of the most unfavourable trends in the eating habits of secondary school students in the Netherlands, that contributes to weight gain, is the decrease in fruit and vegetable consumption. Before the effect of self-efficacy on fruit and vegetable consumption can be examined, reliable and valid instruments have to be developed. The purpose of this research was to develop and test a ‘fruit self-efficacy’ (FSE-)instrument and a ‘vegetable self-efficacy’ (GSE-)instrument for secondary school students in the Netherlands. The research question was: What is the reliability and validity of the FSE-instrument and GSE-instrument? Design: Research aimed at developing and testing instruments can be characterized as methodological research. Setting/Subjects: Secondary school students (11-19-years-old) in the Netherlands completed the two developed instruments during class hours (n=466). Fewer students participated in the second round (n=106). Results: First, the relevance of the twenty-two items of the two developed instruments was evaluated on two occasions by four experts. This procedure resulted in seventeen items for both instruments. Further analysis was based on the responses of the students. Factor analysis identified two unidimensional instruments. Cronbach's alpha for the FSE-instrument was 0.94 and for the GSE-instrument 0.95. The intra-class correlation coefficient between test and re-test of both instruments ranged between 0.33 and 0.84 (P<0.05), depending on the method of completing the instruments (in the classroom or on one’s own initiative) and the order of completing the instruments (started or ended with another instrument in the context of a similar study). The correlation between FSE and fruit consumption was 0.41 (P<0.01), and for GSE and vegetable consumption it was 0.32 (P