Course Syllabi . Related societies Personality research conferences Special advice for students Departments of Psychology with Personality Programs Advice for undergraduates . All scientific theories require measurement of the constructs underlying the field.
Personality theories are no different.
Whether we are developing theories of species typical behavior, of individual differences in behavior, or unique patterns of thoughts and feelings, we need to be able to measure the responses in question. The fields of psychometrics and personality assessment are devoted to the study of the measurement of pscyhological constructs associated with personality. Words are seen as random replicates of each other and thus individual differences in total vocabulary size are estimated from observed differences on these smaller samples. As the number of words sampled increases, the correlation of the individual differences within each sample and with those in the total domain increases accordingly. Although CTT and IRT estimates are highly correlated, CTT statistics are based on decomposing the sources of variance within and between individuals while IRT statistics focus on the precision of an individual estimate without requiring differences between individuals.