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Erasmus University Rotterdam Psychology Psychometrics 2.5 Summary
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2.5 PsychometricsChapter 1 Psychometrics and the Importance of Psychological Testing
Psychological tests are used very frequently, and the scores obtained from them can
give us important clues about a person and their wellbeing (iq, depression)
Misinterpretation or misusage of these tests can lead to unbeneficial, wrong results.
If something is not measured well, it cannot be studied with any scientific validity.
Observable behavior and unobservable psychological attributes
Observable attributes: behaviors. Behaviors are measured for 2 purposes.
1. A researcher is interested in a behavior in its own right. (E.g., examining the way
facial expressions affect emotion perception)
2. Observing behavior as a way of accessing unobservable psychological attributes such
as intelligence, depression or extroversion.
o We made an inference from an observable behavior to an unobservable
psychological attribute.
o Validity: if the scores from a measure seem to be actually measuring the
mental state or mental processes.
o Measures in psychology involves some type of theory linking.
o Measurement involves hypothetical constructs (latent variables.)
o Hypothetical construct: theoretical psychological characteristics or attributes
that cannot be directly observed. These are measured with operational
definitions.
All sciences rely on unobservable constructs to some degree and they all measure
those constructs by measuring some observable events or behaviors.
Psychological tests
Psychological test: a systematic procedure for comparing the behavior of two or
more people.
1. Tests involve behavioral samples of some kind.
2. Behavioral samples must be collected in some systematic way.
3. Purpose of the tests is to compare the behaviors of two or more people.
Tests either compare the behavior of different people (interindividual differences) or
the behavior of the same individuals at different points in time (intraindividual
differences).
Purpose of measurement: identify and if possible, quantify inter and intraindividual
differences.
Types of tests
Battery: used to define bundled tests.
Bundled tests: instruments intended to be administered together but are not
necessarily designed to measure a single psychological attribute.
Open ended tests, aptitude tests, intelligence tests, personality tests, attitude surveys.
Tests varying in the answer type required: open ended tests, closed-ended tests,
choosing among alternatives.
Methods used in tests: individually administered tests, group administrations.
, Intended purpose of test scores: criterion referenced tests and norm referenced tests.
Participants are defined into 2 groups (whose performance exceeds the performance
criterion and whose performance does not exceed the performance criterion.)
1. Criterion referenced test scores: seen in settings in which a decision must be made
about a person’s skill level.
2. Norm referenced test scores: used to compare a person’s test score with scores from
a reference sample or a normative sample.
Speeded and power tests.
o Speeded tests: they are time limited. Scored by counting the number of questions
answered in an allocated time period. Accuracy is NOT important.
o Power tests: not time limited. Test items must range in difficulty if scores on
these tests are to be used to discriminate among people.
Performance or behavior based.
o Performance based: performance on an exam. The number of correct questions.
o Behavior based: according your behavior. Smiling.
Psychometrics
Attributes of tests.
1. Type of information generated by the use of psychological tests.
2. The reliability of the data from psychological tests.
3. Issues concerning the validity of data obtained from psychological tests.
Psychometrics: evaluating the attributes of psychological tests.
Galton and psychometrics
Normal distribution
Correlation coefficient
Use of sampling for the purpose of identifying and treating measurement errors.
Focused on variability of human characteristics. (Individual differences)
Differential psychology.
Challenges to measurement in psychology
Complexity of the psychological phenomena: self-esteem, anxiety, depression have
many different aspects to them. Identifying and capturing all relative aspects of them
are hard.
Participant reactivity: the act of measurement can itself influence the psychological
state or process being measured. Knowing that someone is observing you, can
subconsciously affect your answers. Some participants might try to guess the
hypothesis and act accordingly (demand characteristics & social desirability). Some
other participants might change their behavior to convey a poor impression to the
measurer (malingering).
Experimenter bias and expectancy: experimenter bias can influence the task
observations, scoring a test.
Psychologist tend to rely on composite scores when measuring psychological
attributes. (E.g.,10 different questions to measure introversion.) Physical sciences
usually only rely on a single value obtained from a single observation (weight of a
rock.)
, Score sensitivity: the ability of a measure to discriminate adequately between
meaningful amounts or units of the dimension that is being measured.
Lack of awareness of important psychometric information.
Importance of individual differences
Validation process: the process in which a psychologist accumulates evidence that
the scores on a test actually relates to the skill measured. (E.g., A visual attention test
should show the “true” levels of visual attention of the participant.)
Chapter 2 Scaling
Each psychological attribute exists in some quantity.
The measurement process succeeds if the numbers assigned to an attribute reflect the
actual amount of that attribute.
Fundamental issues with numbers
Numerals: used to represent an individual’s level of a psychological attribute.
The property of identity
Sorting people into categories.
Sameness vs differentness.
Individuals within a category should be the same as each other in terms of sharing
psychological feature, but they should be different from the individuals in another
category.
Categories should be mutually exclusive. If a person is classified as having a
behavioral problem, then he/she cannot be classified as not having a behavioral
problem.
Categories must be exhaustive, the person should fall into one and only category.
The property of order
Convey information about the relative amount of an attribute that people possess.
The child who shows the most interest in learning = 1 or A
We do not know how much difference there is between person 1 and person 2
It is an imprecise way of representing psychological differences.
The property of quantity
Numerals reflect real numbers.
They are standardized quantities. The size of a unit will be determined by some
convention.
Real numbers are continuous. They are also often referred as scalar or metric.
The number of 0
1. Absolute zero: Reflects a state in which an attribute of an object has no existence. (0.0
cm long)
2. Arbitrary zero: 0 is an arbitrary point on a scale used to measure that feature. (e.g.,
calendars, clocks. 0 degrees = melting point of ice)
, Generally, 0 does not exist in psychology (0 social skills = not really common. 0
social skills could describe a person who has a relatively low social skills test score)
Mean of z-scores is always 0.
Absolute or relative 0. (Think of a 6th grader who failed to spell all 20 of the words
given. This kid obtained a score of 0 out of 20. But can we say that he has 0 spelling
ability?)
Unit of measurement
Arbitrariness: distinguishes between different kinds of measurement units.
There are three ways in which a measurement unit can be arbitrary.
1. The specific size of something can be arbitrary.
2. Some units of measurements are not tied to any one type of object.
3. When something takes a physical form, some units of measurement can be used to
measure different features of objects.
Standard measures: units of measurements that are based on arbitrary units of
measurement in all three ways when they take a physical form. (pounds, liters)
Most psychological units of measurement are arbitrary in size, but they are typically
tied to specific objects or dimensions.
Arbitrariness of measurement units
Arbitrariness in unit size: feet was used to measure things. (your feet can be shorter
than the average)
Arbitrariness of type of object to be measured. A criterion of one psychological
issue can also be a criterion for something else. (Lack of sleep can be criteria of both
depression and excitement)
Arbitrariness in feature that is measured: you can only measure height with cm
and m, not with kg.
It’s hard to measure psychological problems because they are invisible.
Additivity and counting
Additivity: requires unit size to remain constant; a unit increase at one point in the
measurement process must be the same as a unit increase at any other point.
o If your units were not constant in magnitude, the entire measurement system
would be flawed.
o The size of a measurement unit should not change as the conditions of
measurement change.
o Additive count is not a good measure, since it fails to properly show the level of
measured thing. (2 correct answers to 2 separate questions = 2 level of
knowledge, however the second question was harder therefore the total of
knowledge should have been 4.)
Counts: simply counting something does not qualify as a measurement. Counting is
measuring only when someone counts to reflect the amount of some feature or
attribute of an object.
Reliability
If I do a test over and over again, will I get the same results every single time?
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