Measurement and Diagnostics
Chapter 1: Psychometrics and the Importance of Psychological measurement
Psychological test - a systematic procedure comparing behaviour of two or more people
- tests involve behavioural samples of some kind
- the behavioural samples must be collected in some systematic way
- the purpose of the tests is to compare behaviours of two or more people or to measure the
behaviour of one individual at different points in time
Appealing features of a test:
1. Generality
- the idea of a test is sometimes limited to “paper and pen” tests but psychological tests can come in
many forms
2. Purpose
- the purpose of measurement in psychology is to identify and quantify inter/intra individual
differences
Types of tests
Variations in content Variations in responses Variations in purpose Variations in reaction
achievement tests open-ended criterion referenced speed tests
aptitude tests closed-ended norm references power tests
intelligence tests / / /
personality tests / / /
attitude surveys / / /
Criterion referenced test - most of them seen in settings in which a decision must be made about a
person’s skill level
- cut-off score is established as a criterion
- sorts people into either individuals with exceeding performance or with lower performance
- normed tests
Norm referenced test - used to understand how a person compares to other people
- comparison of the test score of the individual to the test scores of the references sample
- sample is representative of the target population
Speed test - time-limited test
- scored by counting the number of questions answered in a given time frame
Power test - difficulty test
- scored by counting the number of correct answers
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, - items must range in difficulty
Psychometrics - science concerned with evaluating the attributes of psychological tests
- three attributes are of interest:
1. The type of information generated by the test
2. The reliability of data from the test
3. The issues concerning validity of the data obtained from the test
Challenges to measurement in Psychology:
- we can never be sure that a measurement is perfect
- the act of measurement itself can influence the psychological state or process being measured
by the test
- people’s knowledge that they are being observed can cause them to react in ways that are not
100% organic
- some may try to figure out the aim of the test, some may become apprehensive, or change their
behaviour to convey a poor impression
- people collecting the data can bring biases and expectations to their task
Score sensitivity - the ability of a measure to discriminate adequately between meaningful amounts
or units of the dimension that is being measured
________________________________________________________________________________
Chapter 2: Scaling
Measurement - the assignment of numerals to objects or events according to rules
- the events of interest are generally samples of individual behaviours
- the rules are usually scales of measurement
Scaling - the way numerical values are assigned to psychological attributes
The property of identity:
- the most fundamental form of measurement is the ability to reflect “sameness vs differentness”
- individuals who display behavioural
Rules of sorting people:
problems should be similar to each other
1. Establish a category
- people within a category must satisfy the property of and should be different from individuals
identity
with no behavioural problems
2. Categories must be mutually exclusive
- if an individual is a member of one category, he/she - the idea is that objects and events can
cannot be a member of another category
be sorted into categories that are based
3. Categories must be exhaustive
- each person should fall into one category and only on similarity of features
one category - numerals serve simply as labels of
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, categories
- a classification of individual could also involve the presence or absence of problems
The property of order:
- when numerals have a proper of order, they indicate the rank order of people relative to each
other along a dimension
- it conveys more information than proper of identity but it is still limited
The property of quantity:
- when numerals have the property of quantity, they provide information about the magnitude of
differences between people
- at this level numerals are no longer labels but real numbers
- units of measurement must be clearly defined
Arbitrariness of units of measurement:
1. Unit size
2. Some units of measurements are not tied to one object
3. Used to measure different features of objects
________________________________________________________________________________
Chapter 3: Individual differences and correlations
The nature of variability - the assumption that differences exist among people and that a diagnostic
measure is capable of detecting those differences
1. Individual differences
- differences which exist between people
- all research in psychology depend on the ability to measure individual difference
2. Intraindividual differences
- differences that emerge in one person over time or under different circumstances
Variability - differences among the scores within a distribution
- variance is a way of qualifying variability or individual differences
- the variance and the standard deviation reflect the degree to which the scores in a distribution
deviate from the mean of the distribution
-the numerator of the variance is sometimes called the sum
of squared deviations about the mean
-variance in itself is a type of mean
-the average degree to which people differ from one another
Page 3
Chapter 1: Psychometrics and the Importance of Psychological measurement
Psychological test - a systematic procedure comparing behaviour of two or more people
- tests involve behavioural samples of some kind
- the behavioural samples must be collected in some systematic way
- the purpose of the tests is to compare behaviours of two or more people or to measure the
behaviour of one individual at different points in time
Appealing features of a test:
1. Generality
- the idea of a test is sometimes limited to “paper and pen” tests but psychological tests can come in
many forms
2. Purpose
- the purpose of measurement in psychology is to identify and quantify inter/intra individual
differences
Types of tests
Variations in content Variations in responses Variations in purpose Variations in reaction
achievement tests open-ended criterion referenced speed tests
aptitude tests closed-ended norm references power tests
intelligence tests / / /
personality tests / / /
attitude surveys / / /
Criterion referenced test - most of them seen in settings in which a decision must be made about a
person’s skill level
- cut-off score is established as a criterion
- sorts people into either individuals with exceeding performance or with lower performance
- normed tests
Norm referenced test - used to understand how a person compares to other people
- comparison of the test score of the individual to the test scores of the references sample
- sample is representative of the target population
Speed test - time-limited test
- scored by counting the number of questions answered in a given time frame
Power test - difficulty test
- scored by counting the number of correct answers
Page 1
, - items must range in difficulty
Psychometrics - science concerned with evaluating the attributes of psychological tests
- three attributes are of interest:
1. The type of information generated by the test
2. The reliability of data from the test
3. The issues concerning validity of the data obtained from the test
Challenges to measurement in Psychology:
- we can never be sure that a measurement is perfect
- the act of measurement itself can influence the psychological state or process being measured
by the test
- people’s knowledge that they are being observed can cause them to react in ways that are not
100% organic
- some may try to figure out the aim of the test, some may become apprehensive, or change their
behaviour to convey a poor impression
- people collecting the data can bring biases and expectations to their task
Score sensitivity - the ability of a measure to discriminate adequately between meaningful amounts
or units of the dimension that is being measured
________________________________________________________________________________
Chapter 2: Scaling
Measurement - the assignment of numerals to objects or events according to rules
- the events of interest are generally samples of individual behaviours
- the rules are usually scales of measurement
Scaling - the way numerical values are assigned to psychological attributes
The property of identity:
- the most fundamental form of measurement is the ability to reflect “sameness vs differentness”
- individuals who display behavioural
Rules of sorting people:
problems should be similar to each other
1. Establish a category
- people within a category must satisfy the property of and should be different from individuals
identity
with no behavioural problems
2. Categories must be mutually exclusive
- if an individual is a member of one category, he/she - the idea is that objects and events can
cannot be a member of another category
be sorted into categories that are based
3. Categories must be exhaustive
- each person should fall into one category and only on similarity of features
one category - numerals serve simply as labels of
Page 2
, categories
- a classification of individual could also involve the presence or absence of problems
The property of order:
- when numerals have a proper of order, they indicate the rank order of people relative to each
other along a dimension
- it conveys more information than proper of identity but it is still limited
The property of quantity:
- when numerals have the property of quantity, they provide information about the magnitude of
differences between people
- at this level numerals are no longer labels but real numbers
- units of measurement must be clearly defined
Arbitrariness of units of measurement:
1. Unit size
2. Some units of measurements are not tied to one object
3. Used to measure different features of objects
________________________________________________________________________________
Chapter 3: Individual differences and correlations
The nature of variability - the assumption that differences exist among people and that a diagnostic
measure is capable of detecting those differences
1. Individual differences
- differences which exist between people
- all research in psychology depend on the ability to measure individual difference
2. Intraindividual differences
- differences that emerge in one person over time or under different circumstances
Variability - differences among the scores within a distribution
- variance is a way of qualifying variability or individual differences
- the variance and the standard deviation reflect the degree to which the scores in a distribution
deviate from the mean of the distribution
-the numerator of the variance is sometimes called the sum
of squared deviations about the mean
-variance in itself is a type of mean
-the average degree to which people differ from one another
Page 3
