Measuring Personality: Trait Theory
How Do Psychologists Measure Personality?
Personality can be measured in two main ways: through personality scales, which show where someone sits on a continuous dimension, and personality types, which sort people into fixed categories. Trait theorists such as Gordon Allport and Raymond Cattell preferred scales, because they believed personality is built from traits — characteristics that vary in strength from person to person, rather than being simply present or absent.
Trait theory assumes personality is built from stable traits that everyone has to some degree, measured on a scale, rather than fixed types that a person either has or does not have.
Allport’s Trait Theory (1936)
Gordon Allport (1936) argued that each person’s personality is a unique combination of traits, organised into three levels of importance. A cardinal trait dominates a person’s whole life and is obvious to everyone who knows them, though Allport suggested very few people actually have one.
Most people instead have five to ten central traits. These are the traits you might use to describe a close friend in a reference letter — noticeable and fairly consistent across situations. Beneath these sit many secondary traits, which only show up occasionally, such as feeling nervous specifically before public speaking.
Allport’s theory is praised for recognising that personality is unique to each individual, rather than forcing everyone into the same small set of categories. However, it is hard to test scientifically. Cardinal, central and secondary traits are identified through case studies and personal judgement rather than standardised testing, so different psychologists might disagree about which level a trait belongs to, reducing the theory’s reliability.
Raymond Cattell (1946) reduced personality to sixteen trait dimensions using factor analysis, producing the 16PF questionnaire, which is still used in career and personality assessment today.
Cattell’s 16PF (1946)
Raymond Cattell took a more statistical approach. He used factor analysis to examine thousands of words used to describe personality and found they clustered into sixteen underlying trait dimensions, such as warmth, reasoning ability and emotional stability. Each dimension is a continuum — a person can score anywhere between, for example, reserved and outgoing.
This work produced the 16PF, a self-report questionnaire that gives each respondent a score on all sixteen dimensions, building a detailed personality profile. Because it produces numerical scores rather than a single label, employers and researchers can compare people precisely and track how personality relates to real-world outcomes such as job performance.
Trait theories give psychology a scientific, measurable way to study personality — scores from scales like the 16PF can be tested for reliability and compared across large samples. However, self-report questionnaires rely on people answering honestly, and social desirability bias means respondents may present themselves more favourably than is accurate. Trait theory has also been accused of being reductionist: reducing a complex personality to a fixed set of numbers ignores how much behaviour changes depending on the situation a person is in.
The Study: Van Houtte and Jarvis (1995)
Van Houtte and Jarvis (1995) investigated whether owning a pet was linked to healthy psychosocial development in preadolescent children. Their aim was to test whether pet ownership, compared with not owning a pet, predicted differences in self-esteem, self-concept and sense of autonomy. They also measured children's attachment to animals. They studied 130 children aged 8–13 using a matched-pairs design, pairing pet owners with similar non-pet-owners. The children completed questionnaires measuring autonomy, self-concept, self-esteem, and attachment to animals.
The results showed that pet ownership was linked to higher self-esteem, self-concept and autonomy, with the effect strongest for older children (around 10–11 years) just before adolescence. Attachment to animals was similar for pet owners and non-owners. Van Houtte and Jarvis concluded that owning a pet can support a child’s psychosocial development, particularly as they move towards adolescence.
Van Houtte and Jarvis (1995) found that pet ownership, rather than attachment to the animal, was linked to higher self-esteem, self-concept and autonomy, especially in older children approaching adolescence.
The study used standardised, quantitative questionnaires, making it straightforward to repeat and check for reliability. However, all the data came from self-report, so children may have over- or under-estimated their attachment or self-esteem, reducing validity. The sample was 130 white American children, so the findings may not generalise to children from other cultural or ethnic backgrounds.