Supplementary materials to "Signs of change: Estimating the impact of animal cruelty billboards on plant-based and dairy milk consumption in the UK"

We present a field experiment to evaluate a social marketing campaign encouraging people to try plant-based milk. We ran six anti-dairy billboards for one month in a city in the UK. The billboards featured a photo of a suffering dairy cow, a link to a website with information about dairy cow suffering, and an appeal to try plant-based milk. To estimate the impact of the billboards on plant-based and dairy milk consumption, we triangulated three novel data collection methods. First, we compared changes in regional vs. nationwide sales data from two plant-based milk companies. Second, we evaluated the proportion of dairy-free orders from six cafes in the city where we ran the billboards (‘Billboard City’) before, during, and after the campaign. Third, we compared changes in the proportion of household waste representing plant-based or dairy milk in the Billboard City vs. another UK city with no intervention (‘Control City’). Although descriptively, our results appear to be in line with some positive impact of the billboards, ultimately the study design and data were too limited to support a general claim about the impact of the billboard campaign. There were logistical challenges with each data source, as well as too many extraneous factors for the design to account for adequately. We discuss the challenges of field research, the strengths and weaknesses of each novel data collection method, and present considerations for future research.