Psychological testing
Psychological testing is a field characterized by the use of samples of behavior in order to infer generalizations about a given individual. The technical term for the science behind psychological testing is psychometrics. By samples of behavior, one means observations over time of an individual performing tasks that have usually been prescribed beforehand. These responses are often compiled into statistical tables that allow the evaluator to compare the behavior of the individual being tested to the responses of a norm group.
Psychological testing is not the same as psychological assessment. Psychological assessment is a process that involves the integration of information from multiple sources, such as psychological tests, and other information such as personal and medical history, description of current symptoms and problems by either self or others, and collateral information (interviews with other persons about the person being assessed).  A psychological test is one of the sources of data used within the process of assessment; usually more than one test is used.  All psychologists do some level of assessment when providing services to clients or patients, and may use for example, simple checklists to assess some traits or symptoms, but psychological assessment is a more complex, detailed, in-depth process.  Typical types of focus for psychological assessment are to provided a diagnosis, assess level of function or disability, help direct treatment, and assess treatment outcome.  
A useful psychological measure must be both valid (i.e., actually measures what it claims to measure) and reliable (i.e., internally consistent or give consistent results over time).

# Types of Psychological Tests
There are several broad categories of psychological tests:

## Norm-referenced
Norm-referencing tests regard a specific or non-specific topic, often pertaining to the test taker's education, or career. These tests are commonly used in high schools and colleges. The results often correlate to a Bell curve -- with a few participants doing badly, most doing average, and a few doing extremely well. A common norm-referencing test in the United States is the Graduate Record Examination (GRE), which measures the general area of critical thinking, verbal reasoning and quantitative reasoning skills.  In addition, specific GRE subject tests however cover eight broad fields, mainly in the sciences, but also in mathematics and English.

## IQ/achievement tests
IQ (or cognitive) tests and achievement tests are the most common norm-referenced tests. In either of these types of tests, a series of tasks is presented to the person being evaluated, and the person's responses are graded according to carefully prescribed guidelines. After the test is completed, the results can be compiled and compared to the responses of a norm group, usually comprised of people at the same age or grade level as the person being evaluated.
IQ tests (e.g., WAIS-III, WISC-IV, Cattell Culture Fair III, K-BIT (Kaufman & Kaufman, 1990), Universal Nonverbal Intelligence Test) and academic achievement tests (e.g., WIAT, WRAT) are designed to be administered to either an individual (by a trained evaluator) or to a group of people (paper and pencil tests). The individually-administered tests tend to be more comprehensive, more reliable, more valid and generally to have better psychometric characteristics than group-administered tests. However, individually-administered tests are more expensive to administer because of the need for a trained administrator (psychologist, school psychologist, or psychometrician) and because of the limitation of working with just one client at a time.

## Neuropsychological tests
These tests consist of specifically designed tasks used to measure a psychological function known to be linked to a particular brain structure or pathway.  They are typically used to assess impairment after an injury or illness known to affect neurocognitive functioning, or when used in research, to contrast neuropsychological abilities across experimental groups.

## Personality tests
Psychological measures of personality are often described as either objective tests or projective tests.
Objective tests have a restricted response format, such as allowing for true or false answers or rating using an ordinal scale.  Prominent examples of objective personality tests include the Minnesota Multiphasic Personality Inventory, Millon Clinical Multiaxial Inventory-III (Millon, 1994), Child Behavior Checklist (Achenbach & Rescorla, 2001), and the Beck Depression Inventory (Beck & Steer, 1996). Objective personality tests can be designed for use in business for potential employees, such as the NEO-PI, the 16PF, and the Occupational Personality questionnaire, all of which are based on the Big Five taxonomy. The Big Five, or Five Factor Model of normal personality has gained acceptance since the early 1990s when some influential meta-analyses (e.g., Barrick & Mount 1991) found consistent relationships between the Big Five factors.
Projective tests allow for a much freer type of response.  An example of this would be the Rorschach test, in which a person states what each of ten ink blots might be.  The terms "objective test" and "projective test" have recently come under criticism in the Journal of Personality Assessment. The more descriptive "rating scale or self-report measures" and "free response measures" are suggested, rather than the terms "objective tests" and "projective tests," respectively. There remains some controversy regarding the utility and validity of projective testing which is based on Freud's concept of projecting one's own personality attributes onto a neutral stimulus. However, many practitioners continue to rely on projective testing, and some testing experts (e.g., Cohen, Anastasi) suggest that these measures can be useful in developing therapeutic rapport. The most widely used scoring system for the Rorschach is the Exner system of scoring (Exner & Erdberg, 2005). Another common projective test is the Thematic Apperception Test (TAT; Murray, 1943), which is often scored with Drew Westen's (1991) Social Cognition and Object Relations Scales and Phebe Cramer's Defense Mechanisms Manual (1991, 2002).  Both "rating scale" and "free response" measures are used in contemporary clinical practice.
Other projective tests include the House-Tree-Person Test, Robert's Apperception Test, and the Attachment Projective.

## Direct observation tests
Although most psychological tests are "rating scale" or "free response" measures, psychological assessment may also involve the observation of people as they complete activities.  This type of assessment is usually conducted with families in a laboratory, home or with children in a classroom.  The purpose may be clinical, such as to establish a pre-intervention baseline of a child's hyperactive or aggressive classroom behaviors or to observe the nature of a parent-child interaction in order to understand a relational disorder.  Direct observation procedures are also used in research, for example to study the relationship between intrapsychic variables and specific target behaviors, or to explore sequences of behavioral interaction.
The Parent-Child Interaction Assessment-II (PCIA; Holigrocki, Kaminski & Frieswyk, 1999) is an example of a direct observation procedure that is used with school-age children and parents. The parents and children are video recorded playing at a make-believe zoo. The Parent-Child Early Relational Assessment (Clark, 1999) is used to study parents and young children and involves a feeding and a puzzle task. The MacArthur Story Stem Battery (MSSB; Bretherton et al., 1990) is used to elicit narratives from children.  The Dyadic Parent-Child Interaction Coding System-II (Eyberg, 1981) tracks the extent to which children follow the commands of parents and vice versa and is well suited to the study of children with Oppositional Defiant Disorders and their parents.

## Psychological evaluations using data mining
An examiner may use data mining methods to draw inferences from existing records, texts, and datasets about the person. One such technique is the Abika Test. This test involves gathering data on the individual such as public records, behavior history records, consumer activities, shopping histories, memberships in various organizations, court records, demographic data, property deeds, media, public and private databases, newsgroups, opinions expressed in chat rooms, forums, message boards including other methods such as statistical comparisons with peer groups, polling and information submitted by friends, co-workers, relatives. Thus, this technique compiles personality and psychological profiles that are based on inferences developed from existing records.