The concept of personality type was first discussed and explored by Carl Jung and two American psychiatrists Catherine Briggs and her daughter Isabel Briggs Myers. With detailed research by Catherine Myers and her daughter, the personality type of all sixteen types (ESTP - ESFP - ISTP - ISFP - ESTJ - ESFJ - ISTJ - ISFJ - ENTJ - ENTP - INTJ - INTP - ENFP - ENFJ - INFP - INFJ) They categorized and provided the personal type test, now known as the Myers-Berger test. This is a detailed test that measures personality types. According to Catherine Myers's theory, all people fall into one of these sixteen types. This does not mean that humans are not unique.