A call to action for undertaking and sharing formative evaluations of public health campaigns.

Mass media campaigns are common interventions used in public health, but publicly available evaluations of such campaigns are few and far between, and particularly so for formative evaluations. In 2019, the Heart Foundation released a new campaign called 'Heartless Words', including a major advertisement that sparked instant controversy. In the backlash that followed, very little was said about the importance of rigorous pre-campaign formative evaluations and sharing these evaluations for the benefit of other researchers, practitioners and policy makers. We argue the takeaway points of such controversial campaigns are not only whether they provoke certain emotions or discussion, but also whether they are supported by robust formative evaluations that are publicly available. Formative evaluations are crucial in public health so that we can share and learn what works, for whom, and why. We call on researchers and practitioners to develop, implement and, crucially, disseminate formative evaluations for public health mass media campaigns.