Final answer:
Trait theorists assume that personality traits are universal, stable, and measurable characteristics that vary in degree among individuals, influencing their behavior across various situations. They also believe these traits exist along a continuum, rather than being simply present or absent.
Step-by-step explanation:
Trait theorists hold a basic assumption that personality can be understood by identifying and measuring individual traits, which are characteristic ways of behaving. According to these theorists, traits are universal and can be found to varying degrees within every individual. A fundamental aspect of trait theory is the belief that these traits are consistent and stable over time, influencing a person's actions and reactions across different situations and contexts. Early trait theorists, like Gordon Allport, classified thousands of different descriptive words for people's behavior into categories such as cardinal, central, and secondary traits, which capture varying levels of influence in a person's life and behavior.
Later, Raymond Cattell utilized a statistical technique known as factor analysis to condense these numerous traits into a smaller, more manageable set of 16 personality factors. These factors, which he assessed with his 16 Personality Factor Questionnaire (16PF), demonstrated that traits exist along continua rather than as binary present/absent characteristics and that each person exhibits these traits to different extents.