How long does it take you to decide whether or not you like someone you’ve just met? Although we’re told not to make snap judgments about other people, we do just that all the time. And what’s more, many of those quick assessments are reasonably accurate.

Humans and other primates are highly social species, and over millions of years our ancestors evolved powerful intuitions for processing social information. These intuitions take in lots of data points, analyze them, and produce a feeling about the person we’ve just met: likeable or not, friendly or not, trustworthy or not, attractive or not. All of this information processing takes place outside of awareness, and we’re only conscious of the final product—a "gut" feeling about the other person.

It’s not clear what social cues our intuitions are using to make personality judgments, but they’re no doubt based on subtle readings of body postures, facial expressions, and vocal inflections, among other things.

In the lab, personality psychologists generate a number of attributes, such as laziness, self-assuredness, and friendliness. Individuals can then be rated on each of these attributes to create a personality profile. Psychologists use this process to gain insights into how personality perception works. Let’s ask Tim to assess his personality on a number of traits using a 10-point scale. For example, in response to the question “How friendly are you?” Tim can respond anywhere between 0 for “extremely unfriendly” to 9 for “extremely friendly,” with 5 being the midpoint. We can also ask people who know Tim to evaluate his personality.

This process allows us to answer several questions, such as:

Do people view themselves as others see them?
Do other people agree on a particular individual’s personality?
Are people aware of how others perceive them?
There are no straightforward answers to these questions. Rather, they guide us toward the larger issue of whether personality is stable or variable. That is, do we present ourselves as the same person to all people and in all situations? Or, do our personalities fundamentally change as we move from one social encounter to the next? This is an issue that personality psychologists have been grappling with for over a century.

Personality profiles can also be used to estimate how compatible two people are. Despite the common belief that opposites attract, plenty of social psychology research has shown that most successful relationships are based on similarity of personality traits. This is true both for friendships and for intimate relationships.

However, German psychologists Peter Borkenau and Daniel Leising argue in a recent article that using the “raw” data from personality assessments doesn’t lead to good predictions of compatibility. This is because we tend to be close to the average on most of our personality traits, and so we all tend to resemble each other.

But personality is all about individual differences—how I’m different from you and how we’re both different from Tim. Borkenau and Leising maintain that we don’t evaluate people in terms of absolute personality traits but rather in terms of how much we deviate from average.

For example, the average score for a positive attribute such as “friendliness” is higher than it is for a negative attribute such as “laziness.” Knowing that Tim is high on friendliness and low on laziness tells us little about his personality. Instead, we want to know whether he’s more friendly and less lazy than the average person. Borkenau and Lessing propose that these distinctive profiles—describing how we deviate from average—are far better predictors of compatibility than are raw profiles.

Still, getting an accurate personality profile can be difficult due to certain cognitive biases. (Here, by “accurate” we simply mean that all personality evaluations of a person, including that person’s self-report, tend to agree.)

People with high levels of self-esteem tend to describe their own personalities as being close to the average profile. At the same time, people also tend to describe the personalities of people they like as close to average. These findings suggest that we all have a mental model of the average personality profile that we hold as an ideal. Thus, we view people we like—whether ourselves or others—as being closer to this ideal than they actually are.

It probably comes as no surprise that those who’ve known you for a long time are better judges of your personality than are casual acquaintances. Yet those who know us well and like us a lot tend to put a halo around us—seeing our personalities as more like the idealized “normal” than they really are. Ironically, a person who knows you well but doesn’t especially like you may be a better judge of your character than are your family and friends.

https://www.psychologytoday.com/blog/talking-apes/201609/are-you-good-judge-character