The halo effect refers to a bias whereby the perception of a positive trait in a person or product positively influences further judgments about traits of that person or products by the same manufacturer. One of the more common halo effects is the judgment that a good looking person is intelligent and amiable.

There is also a reverse halo effect whereby perception of a negative or undesirable trait in individuals, brands, or other things influences further negative judgments about the traits of that individual, brand, etc. If a person "looks evil" or "looks guilty" you may judge anything he says or does with suspicion; eventually you may feel confident that you have confirmed your first impression with solid evidence when, in fact, your evidence is completely tainted and conditioned by your first impression. The hope that the halo effect will influence a judge or jury is one reason some criminal lawyers might like their clients to be clean-shaven and dressed neatly when they appear at trial.

The phrase was coined by psychologist Edward Thorndike in 1920 to describe the way commanding officers rated their soldiers. He found that officers usually judged their men as being either good or bad "right across the board. There was little mixing of traits; few people were said to be good in one respect but bad in another."* The old saying that first impressions make lasting impressions is at the heart of the halo effect. If a soldier made a good (or bad) first impression on his commanding officer, that impression would influence the officer's judgment of future behavior. It is very unlikely that given a group of soldiers every one of them would be totally good or totally bad at everything, but the evaluations seemed to indicate that this was the case. More likely, however, the earlier perceptions either positively or negatively affected those later perceptions and