Birds of a feather are persuaded together: Perceived source credibility mediates the effect of political bias on misinformation susceptibility

The viral spread of misinformation poses a threat to societies around the world. Recently, researchers have started to study how motivated reasoning about news content influences misinformation susceptibility. However, because the importance of source credibility in the persuasion process is well-documented, and given that source similarity contributes to credibility evaluations, this raises the question of whether individuals are more susceptible to misinformation from ideologically congruent news sources because they find them to be more credible. In a large between-subject pilot (N = 656) and a pre-registered online mixed-subject experiment with a US sample (N = 150) using simulated social media posts, we find clear evidence that both liberals and conservatives judge misinformation to be more accurate when the source is politically congruent, and that this effect is mediated by perceived source credibility. We show that source effects play a greater role in veracity judgements for liberals than conservatives, but that individuals from both sides of the spectrum judge politically congruent sources as less slanted and more credible. These findings add to our current understanding of source effects in online news environments and provide evidence for the influential effect of perceived source similarity and perceived credibility in misinformation susceptibility.