A halo effect is an outcome in one area due to factors derived from another. When good-looking people, for example, are perceived as more intelligent, more successful and more popular, "that's the halo effect in psychology" and it's caused by a cognitive bias, the tendency for an impression created in one area to influence opinion in another area.
Halo effect as a cognitive bias refers to an observer's overall impression of a person, company, brand, or product influencing the observer's feelings and thoughts about that entity's character or properties. It was named by psychologist in reference to a person being perceived as having a halo. Subsequent researchers have studied it in relation to attractiveness and its bearing on the judicial and educational systems. The halo effect is a specific type of confirmation bias, wherein positive feelings in one area cause ambiguous or neutral traits to be viewed positively. Thorndike originally coined the term referring only to people; however, its use has been greatly expanded especially in the area of brand marketing.
The term "halo" is used in analogy with the religious concept: a glowing circle crowning the heads of saints in countless medieval and Renaissance paintings, bathing the saint's face in heavenly light. The observer may be subject to overestimating the worth of the observed by the presence of a quality that adds light on the whole like a halo. In other words, observers tend to bend their judgement according to one patent characteristic of the person (the "halo"), generalizing towards a judgement of that person's character (e.g., in the literal hagiologic case, "entirely good and worthy").
The effect works in both positive and negative directions (and is hence sometimes called the horns and halo effect). If the observer likes one aspect of something, they will have a positive predisposition toward everything about it. If the observer dislikes one aspect of something, they will have a negative predisposition toward everything about it.
Edward Thorndike, known for his contributions to educational psychology, coined the phrase "halo effect" and was the first to support it with empirical research. He gave the phenomenon its name in his 1920 article "A Constant Error in Psychological Ratings". He had noted in a previous study made in 1915 that estimates of traits in the same person were very highly and evenly correlated. In "Constant Error", Thorndike set out to replicate the study in hopes of pinning down the bias that he thought was present in these ratings.
In "A Constant Error in Psychological Ratings", Thorndike asked two commanding officers to evaluate their soldiers in terms of physical qualities (neatness, voice, physique, bearing, and energy), intellect, leadership skills, and personal qualities (including dependability, loyalty, responsibility, selflessness, and cooperation). His goal was to see how the ratings of one characteristic affected other characteristics.
Thorndike's experiment showed how there was too great a correlation in the commanding officers' responses. In his review he stated: "The correlations are too high and too even. For example, for the three raters next studied[,] the average correlation for physique with intelligence is .31; for physique with leadership, .39; and for physique with character, .28". The ratings of one of the special qualities of an officer often started a trend in the rating results. If an officer had a particular "negative" attribute given off to the commanding officer, it would correlate in the rest of that soldier's results.
A person's attractiveness has also been found to produce a halo effect. Attractiveness provides a valuable aspect of the halo effect to consider because of its multifaceted nature; attractiveness may be influenced by several specific traits. These perceptions of attractiveness may affect judgments tied to personality traits. Physical attributes contribute to perceptions of attractiveness (e.g. weight, hair, eye color). For example, someone who is perceived as attractive, due in part to physical traits, may be more likely to be perceived as kind or intelligent. The role of attractiveness in producing the halo effect has been illustrated through a number of studies. Recent research, for example, has revealed that attractiveness may affect perceptions tied to life success and personality. In this study, attractiveness was correlated with weight, indicating that attractiveness itself may be influenced by various specific traits. Included in the personality variables were trustworthiness and friendliness. People perceived as being more attractive were more likely to be perceived as trustworthy and friendly. What this suggests is that perceptions of attractiveness may influence a variety of other traits, which supports the concept of the halo effect.
Dion, Berscheid & Walster (1972) conducted a study on the relationship between attractiveness and the halo effect. Sixty students from University of Minnesota took part in the experiment, half being male and half being female. Each subject was given three different photos to examine: one of an attractive individual, one of an individual of average attractiveness, and one of an unattractive individual.
The participants judged the photos' subjects along 27 different personality traits (including altruism, conventionality, self-assertiveness, stability, emotionality, trustworthiness, extraversion, kindness, and sexual promiscuity). Participants were then asked to predict the overall happiness the photos' subjects would feel for the rest of their lives, including marital happiness (least likely to get divorced), parental happiness (most likely to be a good parent), social and professional happiness (most likely to experience life fulfillment), and overall happiness. Finally, participants were asked if the subjects would hold a job of high status, medium status, or low status.
Results showed that participants overwhelmingly believed more attractive subjects have more socially desirable personality traits than either averagely attractive or unattractive subjects. Participants also believed that attractive individuals would lead happier lives in general, have happier marriages, and have more career success than the others. Also, results showed that attractive people were believed to be more likely to hold secure, prestigious jobs compared to unattractive individuals. Participants however believed that attractive individuals would be worse parents than both average attractive and unattractive individuals.
A study by Landy & Sigall (1974) demonstrated the halo effect on judgments of intelligence and competence on academic tasks. Sixty male undergraduate students rated the quality of essays which included both well and poorly written samples. One third were presented with a photo of an attractive female as author, another third with that of an unattractive female as author, and the last third were shown neither.
Participants gave significantly better writing evaluations for the more attractive author. On a scale of 1 to 9, the well-written essay by the attractive author received an average of 6.7 while the unattractive author received a 5.9 (with a 6.6 as a control). The gap was larger on the poor essay: the attractive author received an average of 5.2, the control a 4.7, and the unattractive a 2.7, suggesting readers are generally more willing to give physically attractive people the benefit of the doubt when performance is below standard than others.
In a study conducted by Moore, Filippou & Perrett (2011), researchers sought to determine if residual cues to intelligence and personality existed in male and female faces by attempting to control for the attractiveness halo effect. They manipulated the perceived intelligence of photographs of individuals, finding that faces manipulated to look high in perceived intelligences were also rated as more attractive. It was also found that the faces high in perceived intelligence were also rated highly on perceived friendliness and sense of humor.
A study by Verhulst, Lodge & Lavine (2010) found that attractiveness and familiarity are strong predictors of decisions regarding who is put in a position of leadership. Judgments made following one-second exposures to side-by-side photos of two US congressional candidates were reasonably predictive of election outcomes. Attractiveness and familiarity were correlated with competence in this study. Candidates who appeared more attractive and familiar were also seen as more competent and were found more likely to be elected. Similar studies (Palmer & Peterson 2012) found that even when taking factual knowledge into account, candidates who were rated as more attractive were still perceived as more knowledgeable. These results suggest that the halo effect greatly impacts how individuals perceive political knowledge and it demonstrates the powerful influence of the halo effect in politics.
This section needs expansion. You can help by adding to it. (April 2014)
Study results showing the influence of the halo effect in the judicial context exist:
A study by Kaplan (1978) yielded much of the same results as are seen in other studies focusing on the halo effect--attractive individuals were rated more highly in qualities such as creativity, intelligence, and sensitivity than unattractive individuals. However, in addition to these results Kaplan found that some women were influenced by the halo effect on attractiveness only when presented with members of the opposite sex. When presented with an attractive member of the same sex, the effect was attenuated for some women. Dermer & Thiel (1975) continue this line of research, going on to demonstrate that jealousy of an attractive individual has slight effect in evaluation of that person. Their work shows this to be more prevalent among females than males, with some females being less influenced by the halo effect.
Kanazawa & Kovarb (2004) have reasoned that if the following four assumptions were true, beautiful people are indeed likely to be more intelligent and provided empirical evidence for these assumptions.
The reverse halo effect occurs when positive evaluations of an individual cause negative consequences. Dermer and Thiel (1975) had female undergraduates rate pictures of highly attractive, moderately attractive, and unattractive females and evaluate them on a number of dimensions. Their hypothesis that jealousy would moderate attractiveness ratings was partially supported. Unattractive raters did not rate attractive females as highly, and thought that they would be less competent parents and more likely to cheat. A follow up study with both men and women participants supported this, as well as showing that attractive women were expected to be conceited and have a higher socioeconomic status. Eagly et al. (1991) also commented on this phenomenon, showing that more attractive individuals of all sexes were expected to be higher in vanity and possibly egotistic. Applied instances of this "Reverse Halo Effect" include negative evaluations of criminals who use their attractiveness to their advantage (Sigall & Ostrove, 1975) and rating a philosophical essay lower when written by a young female than an old male.
The devil effect, also known as the horns effect, is when people allow an undesirable trait to influence their evaluation of other traits.The Guardian wrote of the devil effect in relation to Hugo Chavez: "Some leaders can become so demonised that it's impossible to assess their achievements and failures in a balanced way."
The relation of a crime to attractiveness is also subject to the halo effect. A study presented two hypothetical crimes: a burglary and a swindle. The burglary involved a woman illegally obtaining a key and stealing $2,200; the swindle involved a woman manipulating a man to invest $2,200 in a nonexistent corporation. The results showed that when the offense was not related to attractiveness (as in the burglary) the unattractive defendant was punished more severely than the attractive one. However, when the offense was related to attractiveness (the swindle), the attractive defendant was punished more severely than the unattractive one. The study imputes that the usual leniency given to the attractive woman (as a result of the halo effect) was negated or reversed when the nature of the crime involved her looks.
Abikoff et al. (1993) found the halo effect is also present in the classroom. In this study, both regular and special education elementary school teachers watched videotapes of what they believed to be children in regular 4th-grade classrooms. In reality, the children were actors, depicting behaviors present in attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), or standard behavior. The teachers were asked to rate the frequency of hyperactive behaviors observed in the children. Teachers rated hyperactive behaviors accurately for children with ADHD; however, the ratings of hyperactivity were much higher for the children with ODD-like behaviors, showing a halo effect for children with ODD.
Foster & Ysseldyke (1976) also found the halo effect present in teachers' evaluations of children. Regular and special education elementary school teachers watched videos of a normal child whom they were told was either emotionally disturbed, possessing a learning disorder, mentally retarded, or "normal". The teachers then completed referral forms based on the child's behavior. The results showed that teachers held negative expectancies toward emotionally disturbed children, maintaining these expectancies even when presented with normal behavior. In addition, the mentally retarded label showed a greater degree of negative bias than the emotionally disturbed or learning disabled.
"In the classroom, teachers are subject to the halo effect rating error when evaluating their students. For example, a teacher who sees a well-behaved student might tend to assume this student is also bright, diligent, and engaged before that teacher has objectively evaluated the student's capacity in these areas. When these types of halo effects occur, they can affect students' approval ratings in certain areas of functioning and can even affect students' grades." (Rasmussen, Encyclopedia of Educational Psychology, Volume 1, 2008)
"In the work setting, the halo effect is most likely to show up in a supervisor's appraisal of a subordinate's job performance. In fact, the halo effect is probably the most common bias in performance appraisal. Think about what happens when a supervisor evaluates the performance of a subordinate. The supervisor may give prominence to a single characteristic of the employee, such as enthusiasm, and allow the entire evaluation to be colored by how he or she judges the employee on that one characteristic. Even though the employee may lack the requisite knowledge or ability to perform the job successfully, if the employee's work shows enthusiasm, the supervisor may very well give him or her a higher performance rating than is justified by knowledge or ability." (Schneider, F.W., Gruman, J. A., & Coutts, L. M., Applied Social Psychology, 2012)
The halo effect is also present in the field of brand marketing. One common halo effect is when the perceived positive features of a particular item extend to a broader brand. A notable example is the manner in which the popularity of Apple's iPod generated enthusiasm for the corporation's other products. Another example is Subway's brand image as a "healthy" variety of fast food. The perception of a restaurant as "healthy" causes consumers to underestimate the caloric content of its dishes. Marketers take advantage of the halo effect to sell products and services. When a celebrity spokesperson endorses a particular item, targeted people's positive evaluation of that individual can influence their perception of the product itself. Job applicants are also likely to feel the impact of the halo effect. If a prospective employer views the applicant as attractive or likeable, they are more likely to also rate the individual as intelligent, competent, and qualified.
The term health halo has been used regarding labeling and marketing of food items. A 2007 study showed that people perceived a Subway meal described as "healthy" as having up to 35 percent fewer calories than a McDonald's meal with identical caloric content.
The term "halo effect" has also been applied to human rights organizations that have used their status to move away from their stated goals. Political scientist Gerald Steinberg has claimed that non-governmental organizations (NGOs) take advantage of the "halo effect" and are "given the status of impartial moral watchdogs" by governments and the news media.
The Ronald McDonald House, a widely known NGO, openly celebrates the positive outcomes it receives from the halo effect. The web page for the Ronald McDonald House in Durham, North Carolina, states that 95% of survey participants were aware of Ronald McDonald House Charities. This awareness is attributed to the halo effect, as employees, customers, and stakeholders are more likely to be involved in a charity that they recognize and trust, with a name and logo that are familiar.
A brand's halo effect can protect its reputation in the event of a crisis. An event that is detrimental to a brand that is viewed favorably would not be as threatening or damaging to a brand that consumers view unfavorably.
Non-psychology/business use of the term "halo effect" can refer to the monetary value of expenditures either in subsequent time periods 
A published 2012 study included this additional usage as "Lastly, there are halo effects; for instance, spend on TV was found to be influencing response in other channels."
Murphy, Jako & Anhalt (1993) argue: "Since 1980, there have been a large number of studies dealing directly or indirectly with halo error in rating. Taken together, these studies suggest that all seven of the characteristics that have defined halo error for much of its history are problematic and that the assumptions that underlie some of them are demonstrably wrong." Their work claims that the assumption that the halo effect is always detrimental is incorrect, with some halo effects resulting in an increase in the accuracy of the rating, in their opinion. Additionally, they discuss the idea of "true halo"--the actual correlation between, for example, attractiveness and performance as an instructor--and "illusory halo" that refers to cognitive distortions, errors in observation and judgement, and the rating tendencies of the individual rater. They claim that any true differentiation between true and illusory halos is impossible in a real-world setting, because the different ratings are strongly influenced by the specific behaviors of the person observed by the raters.
A study by Forgas (2011) states that one's mood can affect the degree of the halo effect's influence. When someone is in a favorable mood, the halo effect is more likely to be influential--this was demonstrated by study participants choosing between pictures of an elderly man with a beard and a young woman, and deciding which subject possessed more philosophical attributes. Additionally, when asked to list the happy times in their life, the halo effect was more evident in the perceptions of the participants. Forgas's study suggests that when one is gauging the extent of the halo effect in a situation, one must consider the emotional state of the person making the judgment.