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Summary Course 2.5 Psychometrics
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Psychology Course 2.5 Psychometrics (2016-2017)PSYCHOLOGY YEAR 2
PSYCHOMETRICS
This course will feature the following topics:
× Know, understand and explain the importance of psychological measurement
× Know, understand and apply principles of scaling
× Understand, apply and analyze individual differences and correlations
× Understand and analyze test dimensionality and factor analysis
× Know and understand the conceptual basis of reliability
× Know, understand, apply and analyze empirical estimates of reliability
× Understand and apply the importance of reliability
× Know, understand the conceptual basis of validity
× Analyze and evaluate empirical estimates of validity
× Know, understand, analyze and evaluate threats to psychometric quality
Exam components during the course:
× Attendance requirement (100% attendance)
× Course exam on the 16th of March (40 multiple-choice questions)
× Practical assignments
Page 1 of 40
,Psychology Course 2.4 Perception (2016-2017)
FURR & BACHARCH CHAPTER 1
Almost every member of an industrialized society is affected by psychological measurement at some point in his or her life; both directly
and indirectly. The outcome of psychological measurements can be long-lasting and important to the people who concerns this. That is
why it should be conducted with the strongest possible tools and procedures. The principles that are discussed in this course are important
for creating tests that are psychologically meaningful and trustworthy. These principles are called psychometrics.
When something is not measured well, it cannot be studied with scientific validity. People use many kinds of instruments to
measure the observable properties of the physical and non-physical world (e.g. measuring how tall a table is with a tape measure vs.
measuring the passing of time with a clock). Physical events in psychology usually includes kinds of behavior. This can either be done
with the goal to study the behavior itself or the deeper, underlying non-physical events like IQ, depression or extroversion. In order to do
this, we have to make interferences about an overt behavior. We assume that what we can observe has a relation with the non-physical
behavior. This relates back to validity (1; you measure what you want to measure and not something different). Then, the interpretation
of the test we use should have a link to the thing we want to measure (2; e.g. trying to measure working memory by letting people run
100 meter is not very effective). Last, we often find theoretical concepts (3; e.g. IQ or working memory) and try to explain those based
on real life observations. These are also called hypothetical constructs or latent variables. The procedure that is used to measure
hypothetical constructs are called operational definitions.
Cronbach (1960) said that a psychological test is a systematic procedure for comparing the behavior of two or more people.
This involves three important components: the data includes behavioral samples of some kind (1), this is collected in a systematic way
(2) and the purpose is to compare behavior of two or more people (3). This is a very general definition that could apply to any kind of test
(e.g. paper-and-pencil vs. running) with any kind of outcome (e.g. categorical vs. data). The purpose of most psychological tests is to
compare behavior of different people (inter-individual difference) or the behavior of the same individuals at different point in time or
under different circumstances (intra-individual differences).
Tests can vary in content (e.g. personality test vs. IQ test), type of response that is required (e.g. open-ended tests vs. close
ended tests), and methods that are used to administer them (e.g. to individuals or to groups). What is often different as well is the purpose
of the test scores. Criterion-referenced tests are most often seen in settings in which a decision must be made about a person’s skill
level which is compared to a fixed standard. Norm-reference tests are usually used to compare a person’s skill level to a reference
sample. This shows you how well a person performs in comparison to other people. In practice, the line between those two tests are a
bit blurry. Other kinds of tests are speeded tests which are time-limited and power tests which are not time-limited. In a speeded test it
is a challenge to answer as much questions as possible. In a power test it is a challenge to answer all the questions and answer them
correctly.
Psychometrics is the science that is concerned with evaluating the attributes of a psychological tests. The attributes will include:
the type of information that is generated by the test (1), the reliability of data from psychological tests (2), and issues concerning validity
of data obtained by the tests (3). Psychological tests are often conceptualized based on hypothetical constructs and theoretical concepts
(e.g. validity or reliability). Psychometrics is about the procedures used to estimate and evaluate the attributes of tests.
Francis Galton was obsessed with measurement. He referred to the measurement of mental features as psychometry which
he defined as the art of imposing measurement and number upon operations of the mind. He is considered the founding father of modern
psychometrics. He started with the normal distribution, correlation coefficient and sampling for the purpose of identifying and treating
measurement error. Galton was interested in the ways people differ from each other.
When you are measuring, you should be able to trust your tools. Another challenge is participant reactivity. People usually
know that they are being tested. Therefore, their response can be influenced by the way they want to be seen (social desirability e.g.
not racist). Some participants will try to figure out the purpose and change their response based on this (demand characteristics). This
influences the validity. Another challenge is that people who observe the behavior can bring biases and expectations to their tasks.
Expectation and biases are difficult to detect because they can even happen unconsciously. Score sensitivity refers to the ability of a
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,Psychology Course 2.4 Perception (2016-2017)
measure to discriminate adequately between meaningful amounts of units of the dimension that is being measured (e.g. feeling good or
bad).
The theme is related to the fact that our ability to identify and characterize psychological differences is at the heart of all
psychological measurement and is the foundation of all methods used to evaluate tests. The purpose of measurement in psychology is
to identify and quantify the psychological differences that exist between people, over time or across conditions. Useful psychometric
information about the samples can be obtained only if people differ with respect to the behavior that we arc sampling. If a behavioral
sampling procedure produces individual differences, then the psychometric properties or the scores obtained from the sampling
procedure can be assessed along a wide variety of dimensions.
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, Psychology Course 2.4 Perception (2016-2017)
FURR & BACHARCH CHAPTER 2
The standard definition of measurement is the assignment of numerals to objects or events according to rules. Events in psychology are
usually subjects and the rules refer to scales of measurement. Scaling is a fundamental issue in measurement, and a full appreciation of
scaling and its implications depends on a variety of abstract issues. We emphasize psychological tests that arc intended to measure
unobservable psychological characteristics, such as attitudes, personality traits, and intelligence. Such characteristics present special
problems for measurement.
In psychological measurement, numerals arc used to represent an individual's level of a psychological attribute. Psychological
measurement is heavily oriented toward numbers and quantification. We must understand three important numerical properties, and we
must understand the meaning of zero. In essence, the numerical properties of identity, order, and quantity reflect the ways in which
numerals represent potential differences in psychological attributes. Furthermore, zero is an interestingly complex number, and this
complexity has implications for the meaning of different kinds of test scores. A test score or 0 Gill have extremely different meanings in
different measurement contexts.
The most fundamental form of measurement is the ability to reflect "sameness versus differentness." For instance, people with
a certain condition are likely similar to each in terms of this psychological feature other and different from people who are not classified
to have this problem. Of course they can differ from the people with the same condition in other features. In psychology we must be able
to sort people into at least two categories (e.g. introverted vs. extraverted).
The property of identity ~ There are certain rules that must be followed when sorting people into categories. The first and most
straightforward rule is that, to establish a category, the people within a category must satisfy the property of identity. That is, all people
within a particular category must be "identical" with respect to the feature reflected by the category (1). Second, the categories must be
mutually exclusive. If a person is classified as having a behavioral problem, then he or she cannot simultaneously be classified as not
having a behavioral problem (2). Third, the categories must be exhaustive. This means that all subjects should fall under at least one
category (3). The categories could be labeled with letters, names, or numerals (e.g. behavior problems =1; no behavior problems = 2).
The numbers in this case do not have a quantitative significance but are code for the categories.
The property of order ~ When numerals have only the property of identity, they convey information about whether two
individuals are similar or different, but nothing more. In contrast, when numerals have the property of order, they convey information
about the relative amount of an attribute that people possess. When numerals have the property of order, they indicate the rank order of
people relative to each other along some dimension. When numerals are used to indicate order, the numerals again serve essentially as
labels. Although the property of order conveys more information than the property of identity, it is still quite limited. While it tells us the
relative amount of differences between people, it does not tell us about the actual degree of differences in that attribute.
Property of quantity ~ When numerals have the property of quantity, they provide information about the magnitude of
differences between people. At this level, numerals reflect real numbers. The number 1 is used to define the size of the basic unit on
any particular scale. All other values on the scale are multiples of I or fractions of 1. Units of measurement are standardized quantities;
the size of a unit will be determined by some convention. For example, 1 degree Celsius (1 "C) is defined in terms of 1/100 th of the
difference between the temperature at which ice melts and the temperature at which water boils. Real numbers arc also said to be
continuous. In principle, any real number can be divided into infinitely small parts. In the context of measurement, real numbers are often
referred to as scalar, metric, or cardinal, or sometimes simply as quantitative values.
The number 0 is a strange number, with a variety of meanings. In one possible meaning, zero reflects a state in which an
attribute of an object or event has no existence. If you said that a subjects has a reaction time of 0, there is no reaction time. Zero in this
context is referred to as absolute zero. The second possible meaning of zero is to view it as an arbitrary quantity of an attribute. A zero
of this type is called a relative or arbitrary zero (e.g. temperature – 0o does not mean no temperature). This often occurs in psychology
because people don’t have zero IQ, self-esteem, introversion or social skills. Despite the fact that most psychological attributes do not
have an absolute 0 point, psychological tests of such attributes could produce a score of 0. In such cases, the zero would be considered
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