Raymond Cattell, another trait theorist who used Psychometric testing to reduce clusters of correlating items in a questionnaire. Cattell used three different types of data in his model.  L data, Q data and T data.

L data:  Life record data. Ratings by observers which Cattell regarded as the best source but which he also recognised are notoriously difficult to make; great skill and time are needed to make accurate ratings.  His research began by identifying all the words in the English language that describe behaviour (trait elements), including more technical terms from Psychology and Psychiatry, and after removing the synonyms (repeated terms) a sample of students was studied for sixth months by trained observers who rated each participant on all of the trait elements.  Data found were ëfactor analysed and 15 first order or source traits were found.

Q data:  Scores from Personality questionnaires.  Based on the original 15 source traits, a large number of questionnaire items were compiled and given to a large number of participants.  When their scores were factor analysed, 16 source traits emerged (12 of the original 15 plus four new ones).  These were used to construct the 16PF (personality factors) questionnaire.  Cattellís questionnaires were not entirely based upon yes no answers, some questions allowed for yes, no and maybe. 

T data:  Objective tests.  These are tests designed specifically to measure personality.  The test involves the completion of a questionnaire and observation.  The purpose of these tests is not revealed to the participants and a number of factors are measured such as reaction time, body sway and body language.  Research into this type of data produced 21 factors altogether, some of which correspond with those produced using Q data.