Psychological Testing & Intelligence
“…the most important aspect of knowledge about genetic variability is that it gives us respect for people’s individual differences. We are not all balls of clay that can be cast in the same mold, or stamped from the same cookie cutter.” –Sandra Scarr.
Psychological Tests
-standardized measure of a sample of behavior History
Francis Galton (1860’s)
-developed measures of
• -sensitivity to high pitched sounds
• -colour perception
• -reaction time
-to assess “intelligence was hereditary”
-tests had no relation to academic/work success.
Alfred Binet (1904)
-created test to assess children
• Assessed abstract reasoning Binet-Simon scale
• They found that tests of practical knowledge, memory, reasoning, vocabulary, and problem solving worked better at predicting school success than the kind of simple sensory tests that Galton had used.
• Their scale expressed a child’s score in terms of ‘mental level’ or ‘mental age’.
• A child’s mental age indicated that he or she displayed the mental ability typical of a child of that chronological age
Lewis Terman and the Stanford Binet -Stanford-Binet Intelligence Scale
• Terman, revised the test by adapting some of Binet’s questions, adding questions appropriate for adults, and establishing new standards for average performance at each age.
• It incorporated a new scoring scheme based on the “intelligence quotient” suggested by William Stern.
Adopted an index of intelligence - “intelligence quotient” (IQ) IQ = Mental Age x 100
Chronological Age
IQ is a child’s mental age divided by chronological age, multiplied by 100.
– standardized tests used to assess mental ability & development, in an educational setting.
David Wechsler (1930’s -)
• Adult intelligence scale (WAIS)
• distinguished between verbal and non-verbal intelligence.
• iscarded the intelligence quotient in favor of a new system based on the normal distribution
• Most widely used
Psychological Testing
– mental ability, personality.
Personality scales – measure motives, interests, values, attitudes etc.
Tests of mental ability:
-intelligence (measure general potential), -aptitude (assess potential of specific abilities),
-achievement (assess mastery and knowledge of subjects).
Psychological test is a
“standardized measure of a sample of a person’s behavior”.
Standardization
Standardization refers to the uniform procedures used in the administration and scoring of a test.
i) A strict uniform procedure must be followed when the test is administered (same instructions, same questions, same time limits)
ii) A uniform procedure is followed when the test is scored Test Norms
To standardize scoring system:
• Develop “norms” based on a large sample of people selected to represent the general population.
• Determine where a score ranks in relation to other scores on the test.
• If could not do this then the test would be meaningless.
Percentile Score
• Test norms allow you to convert your ‘raw score’ on a test into a percentile.
• A percentile score indicates the percentage of people who score at or below the score one has obtained.
Standardization Group
The sample of people that the norms are based on is called a test’s standardization group.
• Test norms are based on a large sample of people
• Norms for most intelligence tests are based on samples of 2000-6000 people.
• Intelligence tests have been standardized
Normal distribution – symmetric bell shaped curve that represents the pattern in which many characteristics are dispersed in the population.
Reliability
• repeating test should yield reproducible and consistently similar results.
• No absolute guideline
- depends on nature and purpose of the test.
-low Reliability then one has “measurement error”.
Expressed as: X=T+E,
X represents the measured score T represents the true score E represents the error
How is reliability measured?
-correlate two sets of scores
Correlation coefficient = degree of relationship between two variables.
Range: –1 to +1
-the closer the value is to 1, the stronger the relationship.
“+” : high scores on variable X are associated with high scores on variable Y and vice versa
“-“ : high scores on variable X are associated with low scores on variable Y.
Measuring reliability:
a) test –retest reliability
-compare the subjects’ scores on two administrations of the test.
-source of error due to time-sampling -due to carry-over effects -due to practice effects b) alternate/parallel forms retest
-source of error due to item sampling
- some items may be more difficult then other items c) split half reliability
-divide the test in half and administer each half separately.
-source of error due to lack of internal consistency.
-possible that some items do not measure the same factor/attribute/ability consistently d) inter-rater reliability
-used when subjective judgements are part of the scoring procedure.
-correlate different judges responses.
-source of error due to observer differences.
- Most reliability estimates are above .70 and many exceed .90.
Validity
- the test measures what it was designed to measure.
Content validity
– degree to which the content of the test represents the domain its supposed to cover.
Criterion related / empirical validity
-test score is correlated with external criterion.
Construct Validity
-used when measuring a variable that is abstract and there are no available criterion to compare it to.
-hypothesize a construct from a theory - generate predictions from the theory.
-test results from several converging studies
- confirm the original predictions used to create the construct.
Intelligence Testing What is intelligence?
Spearman – all people possess in varying amounts a specific core mental ability.
-called it a General intellectual ability (g factor)
-people also have specialized intellectual ability (s factor).
Wechsler defined intelligence as “the global capacity of the individual to act purposefully, to think rationally and to deal effectively with his/her environment”.
Thurston – carved intelligence into seven distinct “primary mental abilities” (word fluency, verbal comprehension, spatial ability, perceptual speed, numerical ability, inductive reasoning, and memory).
Cattel divided the “g factor” into
• “fluid intelligence” determined by biological factors,
-involves reasoning ability, memory capacity, and speed of information processing.
• “crystallized intelligence” determined by education and experience -refers to acquired knowledge and skills in problem solving.
Sternberg’s triarchic theory of intelligence
- Sternberg’s model of intelligence consists of three parts a) Contextual
b) Experiential c) Componential
Gardner – many kinds of intelligence
-people who score high in one area do not necessarily score high in another area.
Eg idiot savants.
Two general categories of intelligence tests 1) Individual Tests.
-not given routinely -examiner plays a key role
-subjective judgement is used to evaluate and score the subjects’ responses.
-extensive training is required in order to administer the test.
• Binet – designed a test that predicted how well a child would do in school.
-he assumed that a poorly performing child was like a normal child but slowed/retarded in mental growth.
-therefore, from test results calculated a mental age (MA) and compared it to a chronological age (CA).
-his test was adapted and modified by psychologists at Stanford University
-the test measures reasoning ability in numerous areas -verbal domain
i) vocabulary (define “dollar”),
ii) comprehension (“where do people buy food) iii) absurdities (identify the funny aspect of a picture)
iv) verbal relations (name the similarities and differences for “scarf, tie, muffler, shirt”
-quantitative domain i) arithmetic (7+18=__)
ii) number series (what are next two numbers in the series 20, 16, 12, 8 __, __) iii) equation building (2 3 5 + =)
-abstract/visual domain
i) pattern analysis, (block design)
ii) copying (geometrical pattern) -memory
i) visual memory with beads ii) auditory memory for sentences iii) auditory memory for digits iv) visual memory for objects
• Wechsler –intelligence test for adults.
Wechsler Adult Intelligence Scale (WAIS) -discarded the measurement of an IQ
-instead the scoring system is based on the normal distribution with a mean of 100 and a standard deviation of 15.
-scores are expressed as deviation scores - assessed verbal as well as performance skills 2)Group Testing
Advantages
• cost efficient
-paper and pencil, no training, self administered, machine scored.
• objective
• broader application, i.e, used in schools, research, business, etc.
Disadvantages
a) no subjective interpretation
b) variability between tests for reliability, validity, standardization.
-therefore,
⇒ use results with caution,
-corroborate scores with other information
⇒ be suspicious of low scores.
-is subject motivated, well rested, and can read and understand the test.
⇒ consider wide discrepancies between performance on different tests a warning signal.
⇒ When in doubt, refer for individual testing.
Summary: intelligence tests sample some mental abilities that assess academic/verbal intelligence.
-but, only the abilities important to western cultures are assessed.
Test Bias and Discrimination
-constructed by white middle class Americans
- draw on experience and knowledge typical of their lifestyle.
-typical answers standardized from white middle class Americans.
Test biases may cause the differences observed on intelligence tests
i.e, on average “white” people tend to score 3-15 points higher then some minority groups in USA.
Does intelligence testing predict job performance or success?
i) correlation between IQ test performance and attainment of high status jobs.
-but motivation more important
• no correlation between IQ and success within a particular area.
Why? –statistics inappropriate
Eg., What we have: What we want:
-practical or social intelligence may become better predictors of job performance.
Therefore, court rulings/laws require tests used in employment selection measure specific abilities clearly related to job performance.
Intelligence and the nature (genetics)/nurture (environment) debate Genetics
-compare the intelligence of people who share different degrees of genetic relatedness -what happens when the environment is different/same?
Heritability Estimates
• A heritability ratio is an estimate of the proportion of trait variability in a population that is determined by variations in genetic inheritance
Limitations of Hereditability Estimates - Estimates is a group statistic
- Heritability of a specific trait may vary from one group to another - Heritability does not tell us about the source of mean group differences.
- Does not tell us about the effects of environmental changes on the mean level of a trait.
Environment
Environmental Deprivation and Enrichment
• Cumulative deprivation hypothesis – children who are raised in substandard circumstances should experience a gradual decline in their IQ as they grow older.
Degradation of an environment can reduce IQ.
– the longer people lived in isolated areas the more the IQ dropped.
Enriched environment can increase IQ.
– orphans
children adopted in to advantaged homes: IQ _10-12 points – The interaction between Nature and Nurture both combine to shape us.
The Flynn Effect
– Flynn Effect deals with how IQ scores of a population change over time The interaction between Nature and Nurture
-both combine to shape us.
How do genes and environment interact?
• Heredity and environment both influence intelligence to a significant degree
• Born with genetically predetermined limits
– “Reaction range” (approx. 20-25 points on the IQ scale)
– The quality of the environment determines where one falls within this “range”.
Culture Free Testing
- Minimize the language/verbal requirements - Typically visual spatial tests
