Intelligence is often defined as a measure of general mental ability. Of the standardized intelligence tests, those developed by David Wechsler are among those most widely used. Wechsler defined intelligence as “the global capacity to act purposefully, to think rationally, and to deal effectively with the environment.” While psychologists generally agree with this definition, they don’t agree on the operational definition of intelligence (that is, a statement of the procedures to be used to precisely define the variable to be measured) or how to accomplish its measurement.
Test Construction- To be useful must use established criteria of standardization, reliability, and validity
Standardization – process of making uniform and objective both testing procedures and scoring procedures in order to obtain meaningful scores.
Reliability – refers to the consistency of results. Different types:
- test and retest reliability – comparison of original test scores with retest scores
- alternate form reliability – comparison of scores obtained on alternate forms of a test
- split-half reliability – comparison of scores obtained on two halves of tests
Validity – refers to the extent that a test measures what it is supposed to measure. Types include:
- content validity – the extent to which a test reflects a sample of the behavior to be measured
- predictive validity – the extent to which a test can predict a person’s behavior in another situation
- face validity – how appropriate a test ‘appears’ to be, just from the way the items read
- construct validity – how well a test assesses the construct for which it was designed
- concurrent validity – how well the results of a test agree with those of a new test or a different form of the test measuring for the same construct
Measures of Intelligence. Several individual tests have been used to test intelligence.
The Binet-Simon intelligence scale, Developed by Frenchmean Alfred Binet, was administered to children to evaluate their performance (mental age) at a given chronological age, this measure called a mental quotient, was used to evaluate a child’s learning potential.
Lewis Terman of Stanford University revised the Binet scale, called the Stanford-Binet intelligence scale, it introduced the concept of intelligence quotient David Wechsler developed the WAIS and the WISC, the revised forms of these tests are still widely used. They contain two subscales, verbal and performance.
Tests of aptitude and achievement. Group tests, like the SAT measure aptitude, or the capacity to learn and achievement, what has been learned.
Ranges of intelligence scores. The two extremes of levels of intellectual functioning are known as developmentally disabled and gifted.
Those identified as mentally retarded or developmentally disabled have IQ scores of 70 or below. Mild (50-70), moderate (35-50), severe (20-35), profound (below 20). Causes include Down syndrome, a genetic disorder; phenylketonuria, a metabolic disorder; and developmental disability due to anoxia (lack of oxygen) during gestation.
The gifted usually fall within the upper 2% to 3% of the IQ score distribution (between 130 and 145). Louis Terman’s study of the gifted found they possess high IQ but also superior potential in any of six areas; general intelligence, specific aptitudes, creativity, leadership, performing arts, and athletics.
Other concepts of intelligence-
Spearman’s two-factor theory. Charles Spearman believed intelligence was made up of two components; a g-factor (general intelligence) and s-factors (a collection of specific cognitive intellectual skills)
Thurstone’s primary mental abilities. L.L. Thurstone proposed seven categories of primary mental abilities: verbal comprehension, number, spatial relations, perceptual speed, word fluency, memory, inductive reasoning or general reasoning. Each ability could be measured separately and the sum composes intelligence.
Guilford’s three-dimensional model. Proposed three dimensions of mental ability:
- operations- the act of thinking
- contents – the terms used in thinking
- products of thinking – ideas
Each dimension is subdivided and the combinations can lead to over 100 separate factors.
Fluid and crystallized intelligence. Raymond Cattell and John Horn suggested that the g-factor should be divided into:
- Fluid intelligence- reasoning ability, memory capacity, and speed of information processing. Involves such skills as those requiring spatial and visual imagery and is generally believed to be much less affected by experience and education than crystallized intelligence.
- Crystallized intelligence – concerns the application of knowledge to problem solving. Includes abilities such as reasoning and verbal and numerical skills and is generally believed to be affected by experience and education.
Vernon’s hierarchical model. Suggests that intelligence consists of factors and skills arranged hierarchically. The cognitive factor, at the top, is composed of two skills, verbal/academic and practical/mechanical
Sternberg’s triarchic theory. Concerned with how intelligence is used, theory deals with:
- componential intelligence, includes components essential to acquisition of knowledge and use of problem-solving strategies
- experiential intelligence, reflected in creatively dealing with new situations and combining different experiences in insightful ways
- contextual intelligence, reflected in the management of day-to-day affairs
Gardner’s seven intelligences, Howard Gardner divided intelligence into seven abilities:
Anxiety Disorders – share the common symptom of anxiety
- generalized anxiety disorder, often referred to as GAD (previously called anxiety state)
- obsessive-compulsive disorder
- posttraumatic stress disorder- involves flashbacks or nightmares following a person’s involvement in or observation of an extremely troubling even
Somatoform Disorders- when a person manifests a psychological problem through a physiological symptom
Mood or Affective Disorders- involves extreme or inappropriate emotions
- Major depression also known as unipolar depression- the most common mood disorder. Key factor is the length of the depressive episode. Other symptoms- loss of appetite, fatigue, change in sleeping patterns, lack of interest in normally enjoyable activities, feelings of worthlessness
- Seasonal Affective Disorder (SAD) – experience depression only in certain parts of the year, winter, treated with light therapy
- Bipolar disorder, also know as manic depression- involves both depressed and manic episodes
Theories on causes
- Aaron Beck, cognitive theorist says comes from unreasonably negative ideas that people have about themselves, their world, and their futures- cognitive triad. Also attributional theory applies
- Has been found to correlate with feelings of learned helplessness
- Evidence suggests a biological component- low levels of serotonin
Schizophrenic Disorders – fundamental symptom is disordered, distorted thinking often demonstrated through delusions and/or hallucinations. There are four kinds
- Disorganized schizophrenia- evidence odd uses of language, make up their own words (neologisms), make clang associations, inappropriate affect or flat affect
- Paranoid schizophrenia- delusions of persecution
- Catatonic schizophrenia- engage in odd movements, stupor, move jerkily and quickly for no apparent reason, waxy flexibility. Increasingly rare
- Undifferentiated schizophrenia- exhibit disordered thinking but no symptoms of one of the other types of schizophrenia
Causes- most popular ideas is biological, dopamine hypothesis, people with schizophrenia have high dopamine levels. Also, enlarged ventricles and brain asymmetries, also seems to be genetic predisposition
Who has schizophrenia?
Schizophrenia is one of the most common mental illnesses. About 1 of every 100 people (1% of the population) is affected by schizophrenia. This disorder is found throughout the world and in all races and cultures. Schizophrenia affects men and women in equal numbers, although on average, men appear to develop schizophrenia earlier than women. Generally, men show the first signs of schizophrenia in their mid 20s and women show the first signs in their late 20s. Schizophrenia has a tremendous cost to society, estimated at $32.5 billion per year in the US (statistic from Brain Facts, Society for Neuroscience, 1997).
For more information on schizophrenia go to http://faculty.washington.edu/chudler/schis.html