General intelligence (g) explains a person’s performance on intellectual tests according to Spearman. However, the idea that there is only one factor explaining intelligence is contested. Crystallized intelligence refers to the knowledge of facts. Fluid intelligence refers to the ability to solve new problems and reason.

Fluid intelligence is not stable over time and is disrupted by several factors (e.g. brain damage, age). Crystallized intelligence is relatively stable over time.

The general intelligence test is a method of assessing someone’s intelligence and consists of several sub-tests which assess specific intellectual skills. IQ reflects a person’s overall performance on all subtests in comparison with a group of peers.

There are several forms of the Raven’s Progressive Matrices, including the Standard Progressive Matrices (1), the Coloured Progressive Matrices (2) and the Advanced Standard Progressive Matrices (3).

A lot of consequences (e.g. special education or not) depend on the results of IQ test scores and these consequences treat IQ test scores as absolute numbers. One problem with a classification system is that intelligence tests often do not properly differentiate between participants on the extreme scale of the measure. The Flynn effect also needs to be taken into account when interpreting intelligence tests.

Intellectual tests can provide powerful diagnostic information. However, intelligence tests are not useful for a localized disorder or localized brain damage. There are three levels in intelligence tests in neuropsychological questions:

1. Level of test performance
   This involves the level of performance on the intelligence test. This is related to a person’s background and at this level, the intelligence test can be used for its original purpose.
2. Inventory of disorders
   This level involves employing the intelligence test as a neuropsychological test battery to make an inventory of potential disorders.
3. Statement about abnormal performances on IQ tests
   This level involves abnormal performance on parts of the IQ tests with the goal of distinguishing localized brain damage.

The test administrator needs to communicate clearly (1), be sensitive to the client’s feelings and perceptions (2) and make sure the logistics are in order (3) at the day of the test.

Norm data provides support for making good quality decisions (e.g. generating the cut-off scores for personnel selection). It is imperative to select norm groups with which to compare the client’s raw scores. The accuracy of conclusions depends on the reliability of the test. It is necessary to standardize scores to compare scores of two different constructs (e.g. verbal intelligence and motor skills).

People with lower intelligence have a higher risk of complaints. However, mental health care is aimed at people with average intelligence. It is useful to conduct an intelligence test on everyone but this is expensive so it is more useful to use an intelligence screening. The Screener for Intelligence and Learning Disabilities (SCIL) consists of 14 items aimed at screening intelligence.

The cut-off score for IQ (e.g. <70 IQ is special education) is arbitrary. The cut-off score for an intelligence screener should identify people who are at risk for low IQ. The efficacy of a cut-off score of a screener is used by administering a traditional intelligence test and a screener and check the correlation between the scores.

It is useful to estimate intelligence to predict professional success (1), assess accountability (2), assess school choice (3), determine treatment environment (4), diagnose learning disorders (5), diagnose behavioural problems (6) and diagnose cognitive problems (7).

Intelligence tests are usually administered individually because this provides opportunities for observation (1) and the test leader can positively influence administration and judge reliability (2). The test administration is standardized. This is done to determine the level of intelligence as objectively as possible.

The intelligence test is usually the first test in a battery because the client is still fit (1), it provides structured interaction (2) and it provides the opportunity to adjust instruments (3). However, it might be useful to start with a lighter test because the intelligence test requires a lot of concentration. The intelligence test is also different for different age groups.

The raw score of a test is translated to a norm score for each subtest. The sum of the norm scores is related to IQ and provides confidence intervals. The norm scores are age-dependent standards. The score is uncertain because the test can be unreliable. The unreliability of intelligence tests is larger at extreme scores (1), is recognized by the DSM-5 (2), can be because of disturbing factors (e.g. noise) (3) and because the interpretation of IQ scores requires clinical judgement (4).

The scores of intelligence tests are standardized every few years by administering it to a large group of representative subjects to know the average of different groups of people and set it to 100. This is also done to account for the Flynn effect. The validity of IQ scores is limited in time.

IQ score is influenced by motor behaviour (1), cultural knowledge (2), language (3), intelligence (4), personality (5), motivation (6) and psychological problems (7).

Conscientiousness and openness to experience are possibly related to intelligence. Practice increases scores on intelligence tests. Psychological problems can also contribute to intelligence as assessment is usually done when the problems are severe and this can lead to more stress (1), feeling more insecure (2), low motivation (3), fear of failure (4) and possible interruptions of schooling (5). Substance use is also common during psychopathology.

There are several recommendations for intelligence research for the admitted client:

1. Use the intelligence test for treatment indication.
2. Repeat the intelligence test when conditions have improved.
3. Minimize feelings of insecurity.
4. Minimize the impact of fear of failure.
5. State developmental history and circumstances.
6. State medication that is used.

Medication can have both positive and negative effects on IQ scores. There are several things to consider when deciding on medication use during test-taking:

1. Decide whether ecologically valid or objective measures are more important.
2. Consult the medical doctor.
3. Determine the length of medication use.
4. Wait until the dose of medication is stable.
5. Wait until the withdrawal symptoms after stopping have ceased.