Misinformation interventions decay rapidly without an immediate posttest

In recent years, many kinds of interventions have been developed that seek to reduce susceptibility to misinformation. In two preregistered longitudinal studies (N₁ = 503, N₂ = 673), we leverage two previously validated “inoculation” interventions (a video and a game) to address two important questions in misinformation interventions research: (1) whether displaying additional stimuli (such as videos unrelated to misinformation) alongside an intervention interferes with its effectiveness, and (2) whether administering an immediate posttest (in the form of a social media post evaluation task after the intervention) plays a role in the longevity of the intervention. We find no evidence that other stimuli interfere with intervention efficacy, but strong evidence that immediate posttests strengthen the learnings from the intervention. In study 1, we find that 48 h after watching a video, participants who received an immediate posttest continued to be significantly better at discerning untrustworthy social media posts from neutral ones than the control group (d = 0.416, p = .007), whereas participants who only received a posttest 48 h later showed no differences with a control (d = 0.010, p = .854). In study 2, we observe highly similar results for a gamified intervention, and provide evidence for a causal mechanism: immediate posttests help strengthen people's memory of the lessons learned in the intervention. We argue that the active rehearsal and application of relevant information are therefore requirements for the longevity of learning-based misinformation interventions, which has substantial implications for their scalability.