In 1964, Dr. David W. Merrill, an industrial psychologist and university professor, and psychologist Roger Reid created a personality model that could predict the success in selling and management careers. This model is simple to understand and allows one to find personality styles fast and easily.
Merrill and Reid established four personality categories based on the conclusions of two traits. First, is the personality mostly extroverted (assertive) or mostly introverted (nonassertive)? Second, is the personality mostly empathy-oriented (relationship-oriented) or mostly non-empathetic (not relationship-oriented)? The answers yield four personality types: The Director, The Analytical, The Socializer and The Amiable.