Measuring Individual Differences

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Methods of Measurement
Insight: single/multiple case observations, biological measures of differences, questionnaires, cog. testing, interviews, diaries
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What are psychometrics?
the science of measuring mental capacities and processes
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Adolphe Quetelet (1796-1874)
- systematic application of statistical methods to humans - "social mechanics" or "social physics" - the average man - BMI (Quetelet index) - interest in defining characteristics of normal man (normal distribution)
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Francis Galton (1822-1911)
- influenced by Quetelet - interests centred on differences and deviation from the norm - SD - eugenics
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Latent Traits or Variables
- often unable to measure things we are interested in directly - need to develop ways of measuring underlying (latent) variables: multiple items, reliability and validity, social desirability biases
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Charles Spearman
- theory of intelligence centred on notion of latent variables - early work: correlations between tests of mental ability - proposed existence of underlying common variable - 'G' - theory emerged from stats techniques (factor analysis)
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Factor Analysis
- explores the patterns of correlation between items on a particular measure - form of data reduction: difficult to deal with lot of items on a measure, identifies similarities and patterns, identifies 'latent' variables
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Factor Analysis Cont'd
- aid theory development - used in questionnaire creation to identify how items inter-correlate, eliminates items - previously done by hand (now SPSS)
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General Factor of Intelligence
- Spearman asked ppts. to engage in tests for memory spatial abilities, math abilities, vocab etc. - examine relationship between all scores - identified positive correlation between each of them
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What is 'G'
- general intelligence - central factor influencing cognitive ability
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Two Factor Theory of Intelligence
- 'G' and 'S' (specific intellectual abilities)
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Influence on measurement
- change in attitudes and approaches - move towards rigorous standardised testing to allow for comparison - larger sample, designed to be all inclusive approaches to measuring intelligence
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3 Wechsler Tests
- Wechsler-Bellevue Scale (1939) - Wechsler Adult Intelligence Scale (1955) adults 16-75 - Wechsler Scale for Children (1955) children 5-16
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Raven's Progressive Matrices (1938)
- based on concept of 'g' - aim to develop a test free of cultural influences - overall score based on deviation from standardised norms
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Beyond 'g'
- Perceptual speed - associative memory - spatial visualisations - number - reasoning - word fluency - verbal comprehension
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Multi-Factor Theorists : Raymond B. Cattell (1905-98)
- factor analysis proponent; authored over 30 psychometric tests - 'fluid' intelligence (Gf) vs. crystallised intelligence (Gc) - heritability vs. effects of environment
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Hierarchal Approaches
- final domain of psychometric approaches to intelligence: what becomes between 'g' and 's'? - specific abilities fall into distinct groups or factors e.g. Vernon (1950) and Carroll (1993)
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Combined Models: Cattell-Horn-Carroll
- 16 'broad' intelligences; each of which divides into subcategories - developed in response to a need to practically apply theories of intelligence in a useful way - researchers: aim to define a true model of intelligence
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Combined Models Cont'd
- testers: measure wide range of abilities -> a product of use in wide number of domains - move away from intelligence theorists to more convoluted and diverse measures
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Psychometric vs. Cognitive
- Cog psychologists take a different approach - focus on determining the biological basis of intelligence - intelligence linked to biological and physiological factors
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Brain Volume and Intelligence
- Tiedemann (1836): link with 'mental energy' - 'Crude and Pseudoscientifi' (Gould, 1996) - Imaging techniques (MRI) has allowed for further exploration (McDaniel, 2005 - pos. correlation of .33) - heritability of brain size
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Reaction Time Tests
- Elementary cog. tasks - Reaction time is key - Intelligence determined by speed and accuracy of response - Moderate correlation observed between IQ and reaction time tests (e.g. Deary, Der & Ford; 2001)
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Example: Arthur Jensen (1923-2012)
- supported notion of general intelligence - ECT's do not require any previous knowledge - speed of processing is an underlying marker of intelligence
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What is Inspection Time
the smallest duration for which a stimulus can be presented, and the participant can still accurately report it.
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Uses of Psychometric Testing
1. Selection (school, uni, recruiting) 2. Diagnosis (psychological and physical conditions) 3. Knowledge Development (research) 4 Audit and evaluation (NHS, govt., market research)
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Features of a good psychometric test
1. reliability 2. validity 3. length of test 4. standardisation of administration and ease of scoring 5. comparison e.g. norms 6. potential value of findings for participants
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Are we over-reliant on Psychometrics?
- emphasis on cross-sectional approach - stability of traits/beliefs/behaviours over time - predictive validity - who is conducting test/what happens to info/how, when might it impact - are we over-tested - are outcomes useful and reliable
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What is reliability
Consistency of a measure over time or across different circumstances
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Internal reliability
- the items correlate with each other well - suggests they are measuring the same construct or 'latent' variable
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Test-retest reliability
extent to which the responses on a measure remain stable over time
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Intelligence Tests: Internal Reliability
- Extensive development and revision - items that show low levels of reliability have been omitted
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Intelligence Tests: Test-Retest Reliability
- assumption that intelligence is a stable trait - evidence suggesting that scores on IQ tests fluctuate on re-test (Benson, 2003)
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Jones and Bayley (1941) - Berkeley Growth Study
- cohort of children tested annually - IQ at 18 positively correlated with IQ at 6 and 12 years (r = .77 & r = .89)
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Deary et al (2004) - Scottish Mental Survey
- Correlation of .73 between age 11 and age 77 - intelligence scores age 11 also predictive of survival aged 76; and levels of physical fitness and independence
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What is validity
does a psychometric test measure what we intended it to? does it measure the underlying variable? - Can be established in a number of ways: comparison with similar measures or diagnostic tests
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Do intelligence tests measure what they originally set out to?
- extensive development and refinement according to theory - high levels of concurrent validity with other intelligence tests - some evidence for predictive validity - performance on Raven's found to be best predictor of students GPA
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Are intelligence tests actually measuring intelligence?
- production of an overall score - despite lack of consensus 'g' - IQ tests may only provide narrow insight into our intellectual abilties
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What is the Flynn Effect
Refers to the substantial and sustained increase in intelligence scores over time
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James Flynn (1987, 1994)
- on average, non-verbal tests showed increases of 15 IQ points per generation - verbal tests show more moderate increases
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Explaining the Flynn Effect: Environmental Factors
- length of schooling - test-taking sophistication - parenting styles - nutrition - environmental change (visual stimulation_
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Cultural Issues with measurement
- attempts to ensure tests are 'culture free' - testing for group differences has stimulated social change e.g. absence of differences in intelligence across gender, class and ethnic groups, motivations for and results of psychometric tests not pos
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Intelligence Use of Intelligence Tests: Benson (2003)
move towards more dynamic use of intelligence tests e.g. identify areas of weakness and develop those areas - high stakes - extensive revision of tests
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What are psychometrics?

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the science of measuring mental capacities and processes

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Adolphe Quetelet (1796-1874)

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Francis Galton (1822-1911)

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Latent Traits or Variables

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