Mapping out personalities is useful for choosing a career (1), personnel selection (2) and clinical diagnostics (3). There are three psychometric issues with personality tests:

1. Reliability
   This can be checked by looking at the test-retest reliability (1), the correlations between items (2), inter-rater reliability (3) and the Cronbach’s alpha (4).
2. Validity
   Construct validity can be checked by investigating differences between groups (1), links with other tests (i.e. convergent validity) (2) and the internal structure of the test (3). The link between the measure and tests that measure other constructs is called discriminant validity. Criterion validity (i.e. predictive validity) is also important for the validity of a measure.
3. Standardization
   The scores often require standardization and comparison to an absolute norm (e.g. passing grade) or a relative norm (e.g. other people).

Cronbach’s alpha is the lower-limit for reliability.

Personality traits are relatively stable. The criterion refers to what one wants to predict. Postdictive validity refers to criterion validity with a criterion that lies in the past. Concurrent validity refers to criterion validity with a criterion that is measured at the same time as the predictor. Predictive validity refers to criterion validity with a criterion that lies in the future.

A good reliability is needed for good validity although good validity is not needed for good reliability. Tests are often assessed based on principles of test construction (1), quality of the test material (2), quality of the manual (3), norms (4), reliability (5), construct validity (6), criterion validity (7).

In projective tasks, the subject is presented with a fairly unstructured task and the idea is that everyone will tackle these tasks in their own way, revealing something about their personality traits and preferences. There are several projective techniques:

1. Association methods
   In this method, the subject has to state the first thing that comes to mind after having been presented with a stimulus.
2. Constructive methods
   In this method, the subject has to construct something based on the things that are offered to the subject (e.g. story).
3. Completion methods
   In this method, the subject is given an incomplete task to complete.
4. Choice or ordering methods
   In this method, the subject is required to classify a number of stimuli based on a number of alternatives.
5. Expressive methods
   In this method, the subject is required to draw something (e.g. a tree).

Projective tests usually have a low validity but makes faking good behaviour more difficult.

Observation is used as a method of determining personality traits when it is difficult to obtain this information directly from the subject (e.g. young children). One problem of observation is demand characteristics. Observation can also occur in relatively controlled environments (e.g. giving people clear tasks).

Personality tests have several characteristics:

1. They consist of statements about the person.
2. They consist of several scales (i.e. a collection of items to measure a certain trait).
3. The scales consist of several items.

There are several often-used personality tests:

1. Myers-Briggs Type Indicator (MBTI)
   This questionnaire is mainly used in the context of training, team building and coaching. It measures four traits (i.e. extroverted vs. introverted, sensing vs. intuitive, thinking vs. feeling, judging vs. perceiving) and people score high or low on each trait. It assesses 16 types of personality. However, there is little scientific evidence for the theory it is based on (1), there is a low reliability for the types (2) and there is a poor validity (3).
2. Minnesota Multiphasic Personality Inventory 2 (MMPI-2)
   This questionnaire is used to measure personality and psychopathology. Problems are that it contains a relatively large number of poorly formulated questions (1) and there is a lot of overlap between the scales (2).
3. NEO-PI-R
   This questionnaire is used to measure personality according to the Big Five. It contains five scales and each scale has six sub-scales. Problems are that there is poor criterion validity for the five scales (1) and the formulation of the questions is often complex (2).
4. Five-Factor Personality Inventory II (FFPI-II)
   This questionnaire is used to measure personality according to the Big Five with one scale adjusted to the Dutch population. One disadvantage of this test is that the scores have to be calculated using a computer.
5. Dutch Personality Questionnaire (NPV)
   This questionnaire is used to measure a wide array of personality constructs that are relevant to different practice areas. There are clear similarities between this test and the Big Five. It is a very good test.

Personality is the best predictor of future work performance, after intelligence. There are several problems with personality assessment:

1. Acquiescence
   This is the tendency to agree with questions. This can be prevented by having reversed questions.
2. Careless responding
   This is the tendency to answer questions randomly. This can be detected by including an infrequency scale in the questionnaire.
3. Extremity
   This is the tendency to give extreme answers to questions.
4. Fence-sitting
   This is the tendency to choose the middle option.
5. Social desirability
   This is the tendency to answer questions in a way that will make one look as socially desirable. It is difficult to measure this although there are scales that could be included in a questionnaire for this. Another way to prevent it is to make sure the questions are not too closely related to social desirability or using forced choice.
6. Faking good behaviour
   This is the tendency to deliberately distort the answers to provide people with a positive image of oneself.
7. Faking bad behaviour
   This is the tendency to deliberately distort the answers to provide people with a negative image of oneself. This occurs in clinical situations where people want their disorder to be recognized. This can potentially be detected using an interview.