There are many methods to measure food waste: self-reported questionnaires and food waste diaries, collecting food waste with kitchen caddies, and using photos from participants of their food waste. As a researcher, which of these methods should you use?

As part of the EU project REFRESH, different methods to measure the amount of in-home food waste in households have been compared. A main result is the development of a practical measurement method that is suitable for large surveys.

After consulting experts and examining relevant papers and reports, five main measurement methods have been compared empirically: self-reported questionnaires in a survey, letting participants keep a food waste diary, collecting waste with kitchen caddies, and coding food waste from photographs that participants provide.

In prior studies, food waste has been assessed with general questions, such as "How much uneaten food, overall, would you say you generally end up throwing away of the food that is bought in your household?" or "Which percentage of the food that is bought in your household is discarded?" These types of questions show low levels of reported waste and low variance in answers, and thus appear less appropriate to measure food waste.

This does not imply that food waste cannot be assessed with greater validity in survey questions. We have developed a method in which participants self-report their amount of food waste in the past week. They first indicate the food categories in which waste has occurred from a list of categories, and then indicate for each category the amount of waste in appropriate units (e.g., pieces of fruit, serving spoons of vegetables, portions of cereal). The result is a measurement that is strongly correlated with other measurements obtained by more intensive methods, such as the diary. Across the board, participants underreport their food waste in this survey method, yet, relative differences between households in the amount of food waste can still be assessed.

Our investigation furthermore indicated that kitchen caddies and coding of photographs are also suitable methods to assess food waste. Because these methods require relatively more researcher time and effort, they are especially appropriate in smaller samples. Due to transportation costs, kitchen caddies can be used more readily when food waste in a smaller region is assessed, whereas photos do not have this limitation.

If you are interested in this report, you may also want to read the scientific papers "A picture says it all? The validity of photograph coding to assess household food waste." and "Comparing wasted apples and oranges. An assessment of methods to measure household food waste.".