Reliability and Accuracy of Real-Time Visualization Techniques for Measuring School Cafeteria Tray Waste : Validating the Quarter-Waste Method

Measuring food waste is essential to determine the impact of school interventions on what children eat. There are multiple methods used for measuring food waste, yet it is unclear which method is most appropriate in large-scale interventions with restricted resources. This study examines which of three visual tray waste measurement methods is most reliable, accurate, and cost-effective compared to the gold standard of individually weighing leftovers. School cafeteria researchers used three visual methods to capture tray waste in addition to actual food waste weights for 197 lunch trays: 1) The quarter-waste method, 2) the half-waste method, and 3) the photograph method. Inter-rater and inter-method reliability were highest for on-site visual methods (0.90 for the quarter-waste method and 0.83 for the half-waste method) and lowest for the photograph-method (0.48). This low reliability is partially do to the inability of photographs to determine whether packaged item (such as milk or yogurt) is empty or full. In sum, the quarter-waste method was the most appropriate for calculating accurate amounts of tray waste whereas the photograph method may be appropriate if researchers only wish to detect significant differences in waste or consumption of selected, unpackaged food