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Theories of Intelligence

Psychological Measurements

Lecture, Chapters 9 & 10


Assessment of Intelligence

            In order to measure intelligence, we must first be able to define it.  Unfortunately, of all the major concepts in the field of testing, intelligence is among the most elusive.


            In order to make an assessment of intelligence, we must create some form of  observable translation of an abstract construct



Sir Francis Galton – first cousin of Charles Darwin

Applied Darwin’s concepts of survival of the fittest and individual differences to humans.

Postulated the existence of a “General Mental Ability”

Based upon speed and refinement of sensory responses

Includes measures of sensory discrimination, perceptual speed, and motor coordination

Later discovered that these scores were not highly correlated with each other or with measures of common sense or other intuitively reasonable measures of intelligence



Began theory development in the 1920s.

Cognitive stages of development:

            Sensorimotor (0-2) – reflexes and sensorimotor skills

            Preoperational (2-7) – pretending and the use of symbols

            Concrete operational (7-11) – logical, problem-solving operations

            Formal operational (12+) – applying logic to abstract ideas, forming hypothetical thinking



Began theory development in the 1930s.

Stages of psychosocial development

            Infancy (0-2) – trust vs. mistrust

            Early childhood (2-3) – autonomy vs. shame/doubt

            Play age (3-5) – initiative vs. guilt

            School age (6-12) – industry vs. inferiority

            Adolescence (13-18) – identity vs. identity confusion

            Young adulthood (19-30) – intimacy vs. isolation

            Adulthood (31-60) – generativity vs. stagnation

            Old age (61+) – integrity vs. despair



Binet’s definition of Intelligence

According to Binet, intelligence is the capacity to…

Find and maintain a definite direction or purpose

Make necessary adaptations to achieve a purpose

Engage in self-criticism so that necessary adjustments in strategy can be made.


Binet’s Principles of Test Construction

Age Differentiation – the fact that with increasing age, children develop their abilities; older children thus have greater abilities than do younger children.

General Mental Ability – initially developed by Spearman, the idea that a single general factor (g) underlies all intelligence

            Fluid (gf) intelligence is the ability to reason, think, and acquire new knowledge.

            Crystallized (gc) intelligence is intelligence which has already been acquired.


Binet’s Units of Measure

Mental age is the unit of measure based on a participant’s performance compared with the average performance in a specified age group.

Intelligence quotient (IQ) is the ratio of a participant’s mental age to chronological age, multiplied by 100 (ratio level of measurement).

Deviation IQ – is the standardization of IQ scores among various age groups, with all groups having a mean of 100 and a standard deviation of 15.


2003 edition of the Binet Scale

Age range spans 2 to 85+.

Norms were based on a sample of 4800, stratified by gender, ethnicity, region, and education according to the 2001 census data.

3000 additional individuals were included, encompassing gifted, mentally retarded, ADHD, and those with speech, language, and hearing problems.

Reliability coefficients for overall IQ are .97 or .98 for all 23 age ranges.

Reliability coefficients for nonverbal IQ subscale is .95 and for verbal is .96.


Wechsler Intelligence Scales: WAIS-III, WISC-IV, and WPPSI-III

Motivated by the effort to construct a more appropriate intelligence scale that that of the 1937 Binet scale.

Used a point scale, in which a specific number of credits or points is assigned to each item.

Incorporated performance scales, which measure nonverbal intelligence, requiring participant to do something other than merely answer questions.


Content – 7 Verbal Subtests

            vocabulary – level

            similarities – abstract thinking

            arithmetic – concentration

            digit span – immediate memory, anxiety

            information – range of knowledge

            comprehension – judgment

            letter- number sequencing – freedom from distractibility


Content – 7 Performance Subtests

Picture completion – alertness to details

Digit symbol-coding – visual-motor skills

Block design – nonverbal reasoning

Matrix reasoning – inductive reasoning

Picture arrangement – planning ability

Object assembly – analysis of part-whole relationships

Symbol search – information-processing speed


Scoring of the WAIS-III

The WAIS-III provides a verbal IQ, performance IQ, and full-scale IQ.

Verbal and Performance IQ’s:

            Convert raw scores of each subtest to a scaled score (age-corrected standard score of 10 with             standard deviation of 15)

            Adding the subtest scores within that group

            Converting to IQ’s using a table (mean=100; std=15)

Full-Scale IQ:

            Add scaled scores for both groups.

            Convert to IQ using table of norms


Measurements of Error


WAIS-III has excellent reliability for verbal, performance, and full-scale IQ’s but varies with individual subtests.


WAIS-III has high correlation with prior test, WAIS-R, providing evidence for validity.



WISC-IV is a revised form of the WAIS-III for the purpose of measuring children’s intelligence.


WPPSI-III is a revised form of the WISC-IV for the purpose of measuring youngest children’s intelligence (ages 2.5 years to 7 years, 3 months).