Psychologists seek to measure personality through a number of methods. The most common of these methods include objective tests and projective measures.

Objective Tests

An objective test is a psychological test that measures an individual's characteristics in a way that isn't influenced by the examiner's own beliefs; in this way, they are said to be independent of rater bias. They usually involve the administration of a bank of questions that are marked and compared against standardized scoring mechanisms, in much the same way that school exams are administered. Objective tests tend to have more validity than projective tests (described below); however, they are still subject to the willingness and ability of the examinee to be open, honest, and self-reflective enough to accurately represent and report their true personality. 

The most common form of objective test in personality psychology is the self-report measure. Self-report measures rely on information provided directly by participants about themselves or their beliefs through a question-and-answer format. There are a number of test formats, but each one requires respondents to provide information about their own personality. They typically use multiple-choice items or numbered scales, which represent a range from 1 (strongly disagree) to 5 (strongly agree).

Self-report measure

Self-report measures typically use multiple-choice items or numbered scales, which represent a range from 1 (strongly disagree) to 5 (strongly agree).

Self-report measures are used with both clinical and nonclinical populations and for a variety of reasons, from diagnostic purposes to helping with career guidance. Some of the more widely used personality self-report measures are the Myers-Briggs Type Indicator, Neo Pi-R, MMPI/MMPI-2, 16 PF, and Eysenck Personality Questionnaire.

Myers-Briggs Type Indicator

The Myers-Briggs Type Indicator (MBTI) is based on Carl Jung's theory of personality. The MBTI is one of the most popular personality inventories used with nonclinical populations; it has been criticized, however, for its lack of statistical validity and low reliability. The MBTI measures individuals across four bi-polar dimensions: 

• Attitudes: Extraversion-Introversion. This measures whether someone is "outward-turning" and action-oriented or "inward turning" and thought-oriented.
• The perceiving function: Sensing-Intuition. This measures whether someone understands and interprets new information using their five senses (sensing) or intuition.
• The judging function: Thinking-Feeling. This measures whether one tends to make decisions based on rational thought or empathic feeling.
• Lifestyle preferences: Judging-Perceiving. This measures whether a person relates to the outside world primarily using their judging function (which is either thinking or feeling) or their perceiving function (which is either sensing or intuition). 

Neo Pi-R

The Revised Neo Pi (personality inventory) is designed to measure personality traits using the five factor model. According to the five factor model, the five dimensions of personality lies along a continuum of opposing poles and include Openness to Experience, Conscientiousness, Extroversion, Agreeableness, and Neuroticism.

Minnesota Multiphasic Personality Inventory (MMPI)

The Minnesota Multiphasic Personality Inventory (MMPI) is the most widely used personality inventory for both clinical and nonclinical populations, and is commonly used to help with the diagnosis of personality disorders. It was first published in 1943, with 504 true/false questions; an updated version including 567 questions was released in 1989, and is known as the MMPI-2. The original MMPI was based on a small, limited sample composed mostly of Minnesota farmers and psychiatric patients; the revised inventory was based on a more representative, national sample to allow for better standardization. 

The MMPI-2 takes 1–2 hours to complete. Responses are scored to produce a clinical profile composed of 10 scales: hypochondriasis, depression, hysteria, psychopathic deviance (social deviance), masculinity versus femininity, paranoia, psychasthenia (obsessive/compulsive qualities), schizophrenia, hypomania, and social introversion. There is also a scale for ascertaining risk factors for alcohol abuse. In 2008, the test was revised once more using more advanced methods; this is the MMPI-2-RF. This version takes about one-half the time to complete and has only 338 questions. Despite the new test’s advantages, the MMPI-2 is more established and is still more widely used. Although the MMPI was originally developed to assist in the clinical diagnosis of psychological disorders, it is now also used for occupational screening for careers like law enforcement, and in college, career, and marital counseling (Ben-Porath & Tellegen, 2008).

16 PF

The 16 PF (personality factor) inventory measures personality according Cattell's 16 factor theory of personality. The 16PF can also used be used by psychologists and other mental health professionals as a clinical instrument to help diagnose psychiatric disorders and help with prognosis and therapy planning. It provides clinicians with a normal-range measurement of anxiety, adjustment, emotional stability, and behavioral problems. It can also be used within other areas of psychology, such as career and occupational selection.

Eysenck Personality Questionnaire

The Eysench Personality Questionnaire is based on Eysenck's model of personality, and was developed from a large body of research and laboratory experiments. Eysenck's inventory focuses on three dimensions: psychoticism, extraversion, and neuroticism.

Projective Measures

Projective measures, unlike objective tests, are sensitive to the rater's or examiner's beliefs. Projective tests are based on Freudian psychology (psychoanalysis) and seek to expose people's unconscious perceptions by using ambiguous stimuli to reveal the inner aspects of an individual's personality. Two of the most popular projective measures are the Thematic Apperception Measure and the Rorschach test.

The advantage of projective measures is that they purportedly expose certain aspects of personality that are impossible to measure by means of an objective test; for instance, they are more reliable at uncovering unconscious personality traits or features. However, they are criticized for having poor reliability and validity, lacking scientific evidence, and relying too much on the subjective judgment of a clinician. 

Rorschach Test

The Rorchach test consists of ten inkblots, which were created by Herman Rorschach dribbling ink on paper and then folding over the paper to create a symmetrical design. During the test, participants are shown the inkblots and asked what each one looks like. The test administrator then asks questions about the responses, such as which part of the inkblot was linked to each response. This test can be used to examine a person's personality charactersitics and emotional functioning, and is thought to measure unconscious attitudes and motivations. 

Simulated inkblot

This simulated inkblot is similar to those that make up the Rorschach test; a Rorschach inkblot would be filled in rather than a dotted pattern. 

Thematic Apperception Test

The Thematic Apperception Test (TAT) consists of 30 cards (including one blank card) depicting ambiguous drawings. Test-takers are asked to tell a story about each picture, including the background that led up to the story and the thoughts and feelings of the characters. Like the Rorschach test, the results are thought to indicate a person's personality characteristics and emotional functioning.