The Myers–Briggs Type Indicator (MBTI) assessment is a psychometric questionnaire designed to measure psychological preferences in how people perceive the world and make decisions. The questionnaire was created by Katharine Cook Briggs and Isabel Briggs Myers based on an extrapolation from the typological theories proposed by Carl Gustav Jung's 1921 book Psychological Types (English edition, 1923). Jung had theorized that there are four principal psychological functions by which humans experience the world - sensation, intuition, feeling, and thinking - and that one of these four functions is dominant most of the time.