Personality

A personality trait is "a relatively consistent tendency to think, feel, or behave in a characteristic way across a range of situations"; a personality inventory is a lengthy assessment of personality, in which participants indicate how well certain descriptors apply to them; a personality dimension is a collection of personality traits that tend to pattern together. A personality dimension is also called a superfactor, and includes descriptors such as "conscientiousness" and "neuroticism." Generally, personality inventories assess individuals' self-rankings on a variety of personality traits, and report an average score along any of a number of personality dimensions.

Temperament is "an inclination to engage in a certain style of thinking, feeling, or behaving" which initially arises from the effects of genes and is moderated by the environment. Unlike personality traits, which can be variable across situations (e.g., "I am a talkative person," may be true of you when you are with close friends, but untrue when you are among strangers), temperaments are consistent across situations. Examples of temperaments include sociability and impulsivity.

Personality (temperament and personality traits) are believed to be in part genetically determined due to their consistency across the lifespan, as well as through twin studies and other measures of heritability. (*Recall that studies of heritability measure how much of the variance of a particular feature (e.g., temperament or intelligence) in a population can be related to genetics vs. environmental factors. Heritability does not indicate the probability / proportion of a trait inherited from parents.)

Two well-documented examples of environmental effects on personality are birth order and culture. Birth order is known to affect personality such that oldest and only children tend to be more ambitious, status-seeking, and assertive; whereas youngest children tend to be more agreeable and fun-loving. Culture is known to affect personality through the differences in personality dimensions attested across cultures. Some cultures tend to be more individualistic vs. collectivist (interested in the needs of the group). We also self-assess our personality through the lens of those around us. People who are surrounded by extremely conscientious peers may rate themselves lower on conscientiousness-related traits in personality inventories.