Table 1.

Summary of the different campaign messaging strategies compared in each of our studies

Campaign messaging strategy	Implementation
(1) Microtargeting	Pretest messages → train machine learning models → show people whichever message is predicted to be best for them personally, based on their demographic and psychological traits
(2) Single best message (SBM)	Pretest messages → show everyone the message that performed the best on average in the pretest
(3) Naïve	No pretesting of messages → show people a message selected randomly from the full set of messages