Validity for Classifying the Stages of Change among the Dietary Assessment Methods on Eating Fruits and Vegetables for American College Students

The objective of this study is to establish outcome validity for three instruments that assess whether subjects met recommendations for daily servings of fruits and vegetables for“Stage of Change”research. A convenience sample of 294 college students was recruited from introductory nutrition classes at Michigan State University in the United States. To measure servings of fruits and vegetables, separately, three types of methods (self-rated intake, 24-hour recall and food frequency) were used in comparison to the servings from a three-day food record, the criterion used. The outcome validity was assessed based on whether or not at least two servings of fruits and three servings of vegetables were reported. Validity was assessed by sensitivity, to measure the ability to detect low intakes, and by specificity, to measure ability to detect adequate intakes. Cohen's kappa was used as well to examine the agreement between the three methods and a three-day food record. The results showed, for fruits, the 24-hour recall had the best agreement (recall 0.54, self-rated : 0.31, food frequency : 0.29) with a three-day food record for servings consumed by people in pre-action or post-action stages. Sensitivity for fruit was also best using a recall (0.81). For vegetables, however, all three methods had low agreement (food frequency : 0.27, recall : 0.21, self-rated : 0.17) with the results of the three-day food record. Self-rated intakes for vegetables had the best sensitivity (0.66) and the food frequency had the best specificity (0.73). Therefore, researcher can use the 24-hour recall method to identify people who consume inadequate servings of fruit. To detect adequate vegetable intake, the food frequency was best of the three methods. Accuracy may be improved by probing for vegetables in mixed dishes and on sandwiches. (J Community Nutrition 4(3)： 143∼150, 2002)