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2.5 Psychometrics

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English notes for course 2.5 Psychometrics, it includes summary of relevant literature sources.

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  • 1. september 2020
  • 52
  • 2019/2020
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CHAPTER 1: PSYCHOMETRICS & IMPORTANCE OF PSYCHOLOGICAL MEASUREMENT
 Psychometrics: the principles and concepts for creating tests that are psychologically meaningful and
trustworthy
o Science concerned with evaluating attributes of psychological tests
 Type of information (e.g. scores) generated
 Reliability of data
 Issues concerning validity of data obtained
o It is about the procedures used to estimate and evaluate the attributes of tests
o Differences between people over time and across conditions contribute to test score variability
and are basis of all psychometric information
 Psychometric movements
o General laws for everyone (experimental psychology): Fechner and Wundt
o Individual differences: Quetelet, Darwin, Galton (as founding father of psychometrics -
differential psychology), Cattell were pioneers that studied variability of human characteristics

OBSERVABLE BEHAVIOR & UNOBSERVABLE PSYCHOLOGICAL ATTRIBUTES
 Use instruments to measure observable and unobservable properties e.g. tape measure for length of
tree and clock for time
o Psychological tests as instruments to measure (observable) behavior
 Measure behavior because interested in that specific behavior or as way of assessing unobservable
psychological attributes (e.g. intelligence, depression, extroversion)
 Identify observable behavior that might represent unobservable psychological attribute, state or
process; then measure behavior and try to interpret those measurement in terms of unobservable
psychological characteristics
 E.g. task involving observable behavior (repeat digits) to measure working memory
o Make inference from observable behavior to unobservable psychological attribute = assume
behavior observed is in fact a measure of working memory if inference is reasonable,
interpretation of the behavior has a degree of validity
o Measurement involves some theory linking psychological characteristics, processes or states to
observable behavior thought to reflect differences in the psychological attribute recall task
had to be theoretically linked to working memory
o Working memory itself is a theoretical concept (hypothetical construct or latent variable) but
when measuring assume is more than figment of imagination; procedures used to measure
hypothetical constructs are operational definitions

PSYCHOLOGICAL TESTS
 Psychological test by Cronbach: systematic procedure for comparing behavior of two or more people
allows for generality of tests and type of information produced by tests
o Tests involve behavioral samples of some kind
o Behavioral samples must be collected in some systematic way (standardized conditions)
o Purpose of tests is to compare behaviors (inter and intra-individual differences)

VARIATIONS IN TESTS
 Content = performance (aptitude, intelligence), behavior (personality test)
 Response required = open-ended, closed-ended test
 Methods used to administer them = individually administered, administered to groups of people
 Intended purpose of test scores = criterion-referenced (decision must be made about person’s skill
level, with predetermined fixed score, e.g. 5.5 to pass exam), norm-referenced tests (to compare

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, person’s test score with scores from reference sample thought to be representative of some population,
percentile score, e.g. SAT)
o Scores on norm-referenced test are of little value if: reference sample is not representative of
population, relevant population is not well defined, there is doubt person being tested is
member of relevant population
 Time/accuracy = speeded tests (time-limited, people not expected to complete all questions, questions
have comparable difficulty and scored by counting number questions answered -accuracy not
important), power tests (not time-limited, expected to answer all questions, items range in difficulty
and scored by counting number of correct answers -accuracy is important)

TYPES OF MEASUREMENTS
 Observational measurements
o Direct observation of behavior e.g. reaction time
o Indirect observation e.g. sound recording
 Self-report
o Via questionnaires
o Interview
 Physiological measurements
o Heartbeat
o EEG, fMRI

CHALLENGES TO MEASUREMENT IN PSYCHOLOGY
 Complexity of psychological phenomena: difficult to identify and capture important aspects of
psychological attributes in a single number
 Participant reactivity: act of measuring can influence the psychological state or process begin measured,
people’s knowledge that are being observed can influence the behavior = validity of measure is
compromised
o Try to figure out researcher’s purpose for a study
o Demand characteristics: change behavior to accommodate the researcher
o Become apprehensive
o Social desirability: change behavior to try impress the person doing the measurement
o Malingering: change behavior to convey poor impression to the person doing the measurement
 Biases and expectations to task: people collecting the data can bring biases and expectations to the task
 Composite scores: total score that represents final measure of the relevant construct
 Score sensitivity: ability of a measure to discriminate adequately between meaningful amounts or units
of the dimension that is being measured e.g. measure emotions good/bad vs scale from extremely good
to extremely bad
 Lack of awareness of important psychometric information

CHAPTER 2: SCALING
 Scaling: the way numerical values are assigned to psychological attributes
o Stevens: measurement is the assignment of numerals to objects or events according to rules
 Measured individuals are allocated to a position on a scale (translation of test behavior to test scores)
 Rules for scaling depend on the used statistical model
o Thorndike: if something exists, it must exist in some amount = each psychological attribute
exists in some quantity

FUNDAMENTAL ISSUES WITH NUMBERS

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,  Numerals are used to represent an individual’s level of psychological attribute e.g. IQ score to represent
level of intelligence
 Numerical properties: identity, order and quantity represent differences in psychological attributes

PROPERTY OF IDENTITY
 Most fundamental form of measurement is the ability to reflect “sameness versus differentness”
 Individuals within category should be the same as each other (sharing psychological feature), but should
be different from individuals in another category
 Rules when sorting people into categories
o People within a category must satisfy the property of identity
o Categories must be mutually exclusive
o Categories must be exhaustive
 Numerals serve simply as labels of categories with no mathematical value
 Categories represent differences in kind or quality rather than differences in amount

PROPERTY OF ORDER
 Numerals convey information about the relative amount of an attribute that person has
 They indicate rank order of people relative to each other along some dimension
 Does not tell about the actual degree of differences in the attribute

PROPERTY OF QUANTITY
 Numerals provide information about the magnitude of difference between people, reflect real numbers
(continuous, can be divided into infinite parts)
 Number 1 used to define the size of the basic unit on any particular scale
 Units of measurement are standardized quantities and the size of unit will be determined by some
convention/rule
 Psychological test often assume test scores have the property of quantity

NUMBER 0
 Absolute zero: reflects a state in which an attribute of an object or event has no existence e.g. reaction
time, length, quantity
 Arbitrary or relative zero: arbitrary quantity of an attribute, does not represent the absence of anything
e.g. temperature
 Most psychological test scores can be expressed as a type of z-score
o Mean of distributions will always be zero (arbitrary)

UNITS OF MEASUREMENT
 Property of quantity requires that units of measurement are clearly defined
 In physical measurement units are apparent (cm to measure length) but in psychological measurement
units are less obvious (how measure shyness?)
 Arbitrariness: distinguishes between different kinds of measurement units
 Ways measurement unit might be arbitrary
o Specific unit size is arbitrary = no true value trying to obtain e.g. choice of weight representing a
pound
o Units of measurement are not tied to any one type of object = no restriction to which objects
can be applied e.g. pound to measure weight of apple or elephant
o Some units can be used to measure different features of objects



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