Study 4.

The banners, including the images included and the validity of their content, were pretested in three pilot studies. In the first pilot study (via TurkPrime n = 289), we tested 30 images, including images related to 1) mother–child bonding, 2) nature scenarios, and 3) mother–child bonding in nature. Each image was evaluated using five-point Likert scales based on the following questions: “How much does this picture makes you feel…loved and protected? Safe and secure? Connected to nature?” The image selected (pregnant woman with an Earth-shaped belly—Banner B) was evaluated the highest on these three items.

Next, we scoped websites from environmental non-governmental organizations and international organizations to identify commonly used images that link food waste with carbon emissions. The assessment popularized by Food and Agriculture Organization (62)—that if food waste were a country, it would be the third-largest emitting country in the world—is used frequently in anti–food waste messaging (e.g., https://twitter.com/faoclimate/status/920969081548951552). Therefore, an image representing this information was selected as the alternative, comparative intervention to attachment security.

Finally, both the carbon emissions image and the attachment security image were composed into banners with a header “Reduce the Food You Waste” (as shown in Fig. 3) and also tested via TurkPrime (n = 106). Participants were randomly allocated to see the carbon emissions banner or the attachment security banner. Participants were asked to what extent the banner was…informative? educational? makes you feel loved? makes you feel secure? (1 = strongly disagree to 7 = strongly agree). A factor analysis resulted in two factors (KMO Test = 0.69; Bartlett’s Test of Sphericity = 214.60 and P < 0.001; and cumulative eigenvalue 78.1%): The two first items were about information (r = 0.72) and the last two about attachment (r = 0.86). The banners produced significant differences in these factors. The carbon emissions banner was perceived as more informative [F (1, 104) = 7.59 and P = 0.01], and the Mother Earth banner increased feelings of attachment security [F (1, 104) = 3.97 and P = 0.05]. These quantitative measures were corroborated by free-text analysis: Participants were also asked to briefly describe what the banner was about and what message it was trying to convey. After this empirical verification of predictive validity, the banners were printed in large outdoor-size letters (L: 120 cm and H: 300 cm).

The analysis of food waste in the same cafeteria over time poses some challenges. Observations are not independent per se, because the same population tends to use the cafeteria on a daily basis. On the other hand, there is no recordkeeping of which individuals use the cafeteria each day, and the exact same individuals may not be present on a daily basis. Therefore, a nonparametric option such as the Friedman test could not be selected. We ultimately selected the Mann–Whitney U test as our primary statistical test because of the small and unbalanced sample sizes per time period (i.e., the baseline period lasted 21 d, compared to periods of 8 d, each when the banners were exposed). The Mann–Whitney U test does not assume normality in the data but requires homogeneity of variance. This was confirmed with the Levene’s test (based on median = 1.38 and P = 0.23). Results for differences in food waste per capita in different periods were confirmed with the median test.

We have obtained informed consent from all participants. We obtained ethical approval from the New York University Abu Dhabi internal review board and complied with all relevant ethical regulations for research with human participants. None of our studies involved deception.