Notes de cours
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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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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