Measuring Plate Waste: Validity and Inter-Rater Reliability of the Quarter-Waste Method
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Background Measuring food waste in school cafeterias is an important tool to evaluate the effectiveness of school nutrition policies aiming to increase consumption of healthier meals. Visual assessment methods are frequently applied in plate waste studies because they are more convenient than weighing; the visual quarter-waste method has become one of the most commonly used in studies of school meal consumption, but little is known about its accuracy. Objective The aims of this study were to determine whether the visual quarter-waste method is valid and reliable in a school cafeteria setting when compared to weighing plate waste. Methods Researchers both weighed and visually assessed plate waste from 748 trays in nine middle schools and high schools. In addition, two researchers independently assessed 59 of these trays using the quarter-waste method. The data were analyzed using the weighted Kappa coefficient and interpreted using the scale developed by Landis & Koch. Results For validity, 45% of foods assessed using the quarter-waste method were in “almost perfect agreement” with the measured weight, 42% of foods visually assessed were in “substantial agreement” with the weight, 10% were in “moderate agreement” and 3% were in “slight agreement”. For inter-rater reliability, eight of ten food groups had Kappas in “almost perfect agreement” between the two raters and the other two groups had Kappas in “substantial agreement” between the two raters. Conclusion These results suggest that the quarter-waste method is a valid and reliable tool for measuring plate waste in a school cafeteria setting.
- Nutritional sciences