The halo effect is a form of cognitive bias which causes one part to make the whole seem more attractive or desirable. This concept can be applied to people, products, brands and companies.
This phenomenon can be triggered by various positive traits and is strongly linked with first impressions. Physical attractiveness is a common factor in the halo effect, as someone who is perceived to be more attractive will be assumed to have other positive personality traits and abilities.
Confirmation bias can strengthen the halo effect. Once a positive opinion of a person or product has been formed, positive interactions with that person or product are seen to reinforce that favorable opinion, but negative interactions are often disregarded.
An example of the halo effect is in a job interview. The candidate is much more likely to be hired if he or she appears attractive and friendly to the employer because the employer will associate those external, positive qualities with intelligence, capability and talent, regardless of whether the candidate actually has those characteristics.
Advertisers and marketers often take advantage of the halo effect in their promotions. One common way of doing this is celebrity endorsements. When consumers see a celebrity in an advertisement, the product seems more desirable because of the celebrity's popularity. Another common use of the halo effect is when e-commerce websites offer free shipping when customers spend a certain amount of money -- the promise of free shipping puts the products in a more positive light.
Businesses also use the halo effect by releasing one popular product, which then boosts the appeal of the rest of its products because of that initial product's popularity. For example, Apple's success with the release of the iPod made other Apple products sell better because of the brand association. Car vendors take advantage of this effect as well and often release a model with many special features to make the rest of the line seem more appealing.
The reverse halo effect (sometimes called the "devil horns" effect) is also true in that a negative characteristic will make a person or product seem overall less attractive. Similarly to the negativity bias, this cognitive bias can make negative first impressions have a much stronger impact.
The halo effect was first described in 1920 by psychologist Edward Thorndike in his paper titled "A Constant Error in Psychological Ratings." The paper was based on a study in which he asked commanding officers to rate their soldiers based on certain characteristics. He discovered that the ratings of soldiers' physique were positively correlated with those for intelligence, leadership and character, despite being unrelated characteristics.