“If you cannot measure it, you cannot improve it” is a quote that has been attributed to Lord Kelvin (although in reality his wording was different). In order to check for progress or deterioration, and to understand a phenomenon, we need to ensure accurate and reliable measurements. In some cases, such measurements are readily available, but oftentimes they are not. In a set of recent studies, we attempted to gain more insight into the measurement of a particularly relevant topic in today’s society: household food waste.
A large amount of resources, such as land, water, and energy, is required for the production, transport, packaging, sales, and preparation of food that is never eaten. This also involves the release of greenhouse gasses. In developed countries, most of the food waste is incurred by households. But exactly how much is wasted? How can we measure this?
Scholars have used various different methods for measuring household food waste. They have:
- asked people to keep food waste diaries;
- asked people about their food waste in questionnaires;
- collected and measured food waste put at the curb;
- asked people to put food waste in kitchen caddies;
- asked people to send in photographs of their food waste.
In our study, we have compared five methods (two types of survey questions, diary, kitchen caddy, photograph coding), by asking 143 Dutch panel members to provide measures of their food waste at home using some or all of these methods.
Results show that general survey questions (“how much do you generally throw away” or “how often is food discarded in your household”) lead to large underestimation of the amount of food waste and show little differences between households (even though food wasted in households varies). A better way to measure food waste in questionnaires, is to ask people to indicate from which food categories they discarded products in the past week (e.g., fruit, bread, vegetables), with follow-up questions on the amount (e.g., number of pieces, number of slices, number of spoons). This method can differentiate households according to their amount of food waste, but still underestimates the amount that gets wasted.
For the purposes of obtaining an approximate estimate of food waste and understanding the types of food thrown away, food diaries, kitchen caddies, and photograph coding all seem to be valid methods to measure food waste amounts. In a separate study, we examined photograph coding in more detail by letting coders estimate amounts of food waste on a systematically varied set of photographs. The photographs varied in food amount, food density, size of the ‘container’ (plate, glass, bowl, pan) and food category. Results confirmed that coders can accurately estimate the weight of food waste from these photographs, without general over- or underestimation.
The methods in our study have been assessed on their ability to provide an approximation of the amount of food waste and their ability to differentiate between households in the amount that is wasted. Validity of these and other measures for tracking household food waste over time or evaluating policy interventions designed to reduce household food waste remains an open question for future research.
Read the papers here:
Van Herpen, E., van der Lans, I. A., Holthuysen, N., Nijenhuis-de Vries, M., and Quested, T. E., 2019. Comparing wasted apples and oranges: An assessment of methods to measure household food waste. Waste Management, 88, 71-84. https://doi.org/10.1016/j.wasman.2019.03.013
Van Herpen, E., and van der Lans, I., 2019. A picture says it all? The validity of photograph coding to assess household food waste. Food Quality and Preference, 75, 71-77. https://doi.org/10.1016/j.foodqual.2019.02.006