Abstract
Analogous to side effects in medical research, spillover and halo effects refer to unintended effects of interventions. Tourism and research in related areas have only begun to acknowledge these exist. Future research should quantify their magnitude to enable cost–benefit analysis, for example of whether an intervention to reduce carbon footprint does so when the total effect of interventions is included. Utilizing data from an experiment aimed at changing tourists’ food consumption behaviour in hotels, this paper provides a methodology to quantify spillover and halo effects, including statistical inference to test hypotheses and produce confidence intervals.