Definition
The halo effect is a cognitive bias in which our overall positive impression of a person — often anchored on a single salient trait — generalizes to unrelated positive evaluations. Most commonly the anchor is physical attractiveness: attractive people are perceived as more competent, more honest, more persuasive, and more deserving of help, with no evidence to support these inferences.
The term was coined by Edward Thorndike in 1920 after he found that military officers rating soldiers tended to score them similarly across unrelated traits — a soldier rated high on physique was also rated high on intelligence, leadership, and character. The same effect appears in job interviews, courtrooms, classroom evaluations, and political polls.
Why it matters
How it works
Cognitively, the halo effect is a cousin of the representativeness heuristic — once the brain has formed an overall impression, that impression becomes the dominant cue for subsequent judgments about the same target. Re-deriving each judgment from scratch is more expensive than letting the overall impression cascade, so the brain takes the shortcut.
The effect compounds with confirmation bias: once we've judged someone competent, we notice and weight evidence supporting their competence more heavily than disconfirming evidence. Over time the initial impression can become structurally locked in.
The defense is to evaluate traits independently and in writing. A candidate scoring on five separate dimensions, each rated on its own evidence, will produce a different ranking than the same candidate evaluated in a single gestalt impression. Structured interviews and rubrics are explicitly designed to interrupt the halo.