Where they trying to prove or disprove the theories?
Who did they test?
When was the test done?
Were any enticements offered to get people to do the tests?
Freud would tell you that his work was validated, others would point out that he and his patients skewed the results.
Which are you looking at?
'Why' is the most important question not 'what'
Besides in all your reading of the enneagram does it not seem more competent than say palmistry? I bet if you had your palm read it would give you some insight if only from setting your mind off down a new or rarely travelled path. What more can you ask of a system of analysis?