Big 5 - The Origins

The big 5 was initially developed via the lexical hypothesis. All the words which described human personality in the English language were compiled. Words which had a purely value oriented meaning (e.g. angel, jackass, scoundrel, hero) were excluded. This resulted in a long list of about 1,000 descriptive words. Factor analysis was then carried out to try and reduce the number of traits that were being measured.

What is factor analysis? Let's take the word "orderly". Words like neat, tidy and orderly are essentially synonyms. If we are trying to identify underlying personality traits and a substantial number of the words that we are relying on are just synonyms of each other then we can quickly reduce the pool of words (and possible traits) by grouping these synonyms together. Words like efficient, systematic and businesslike are not exactly synonyms of orderly but they do tend to go together. We would often expect orderliness to lead to efficiency and we would also expect someone who is concerned with orderliness to also be concerned with efficiency. So although these words are not synonyms they do seem to co-occur. It appears that a lot of descriptive words seem, intuitively, to group together. 

This method of reducing words to their underlying groups was continued until the resulting number of categories was in single digits, with 5 being the most widely agreed upon number of categories.

Early personality models which were very similar to the modern big 5 (but which utilised different names for the traits) were generated in this manner.