partisanbias

Partisan bias is the systematic tendency to evaluate political information, actors, and events through the lens of one’s political party, favoring one’s in-group and disfavoring the out-group regardless of objective merits.

It is widely described as a form of identity-protective cognition that shapes perceptions to align with partisan loyalties. Research, including work by Lilliana Mason, shows that partisans often reinterpret facts, overestimate favorable information about their side, and downplay or misremember information that harms it.

Partisan bias can manifest in judgments about policy proposals, candidates, news sources, and scientific claims where perceived alignment with party lines biases assessment. It is typically measured by experiments presenting identical information with partisan cues, surveys on the credibility of sources, and assessments of the gap between factual accuracy and beliefs across groups.

Mechanisms include motivated reasoning, selective exposure to partisan media and social networks, and identity salience that activates confirmation bias and disconfirmation of opposing viewpoints. Contexts that amplify partisan bias include highly polarized environments, strong elite cues, and echo chambers online.

Consequences for democracy include increased polarization, decreased trust in opposing groups, and susceptibility to misinformation. Efforts to mitigate emphasize inoculation against misinformation, exposure to diverse viewpoints, and media literacy, though reducing identity-driven evaluation remains challenging.

Some scholars caution that bias is not uniform and can reflect legitimate disagreements or information gaps; measurement and definitions vary across studies.