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Table of content (Inhoudsopgave)
- Hoofdstuk 1 - Wat omvat de psychometrie allemaal?
- Hoofdstuk 2 - Wat is belangrijk bij het toekennen van cijfers aan psychologische eigenschappen?
- Hoofdstuk 3 - Wat betekenen variabiliteit en covariabiliteit?
- Hoofdstuk 4 - Wat is test dimensionaliteit en wat is factor analyse?
- Hoofdstuk 5 - Wat houdt het basisbegrip betrouwbaarheid in?
- Hoofdstuk 6 - Hoe kunnen empirische schattingen van de betrouwbaarheid worden gedaan?
- Hoofdstuk 7 - Wat is het belang van betrouwbaarheid?
- Hoofdstuk 8 - Wat is validiteit?
- Hoofdstuk 9 - Hoe kun je bewijs voor convergente en discriminante validiteit evalueren?
- Hoofdstuk 10 - Welke soorten reactiebias zijn er?
- Hoofdstuk 11 - Welke soorten test bias zijn er?
- Hoofdstuk 12 - Hoe ziet een confirmatieve factor analyse eruit?
- Hoofdstuk 13 - Wat stelt de generalizability theory (G theorie)?
- Hoofdstuk 14 - Wat stelt de Item Response Theorie (IRT) en welke modellen zijn er?
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What is psychometrics? - Chapter 1
Psychometrics play an important role in daily life. Whether you are a student, teacher, parent, psychologist, mathematician, or physicist; everyone has to deal with psychological tests. Psychological tests can have influenced your educational career, career, health, prosperity and so on. Psychometrics can even influence questions about life and death. For example in some countries, people with a severe cognitive impairment (significantly below average) can not receive the death penalty. But what is significantly below average? And how can we determine if the intelligence of an individual is below this limit? These kind of difficult questions can be answered through psychological tests. All in all, we can therefore say that psychometrics extends beyond psychological research. Psychometrics play a role in daily life, everyone has to deal with it.
How are psychological characteristics measured?
Psychologists use instruments to measure observable situations in the physical world. Sometimes psychologists measure a certain type of behavior solely because they are interested in that specific behavior in itself. But it is mainly behavioral scientists that measure human behavior to measure unobservable psychological attributes. We then identify a certain observable behavior and assume that this represents a certain unobservable psychological process, attribute or attitude. You must ensure that what you are measuring is also what you are aiming to measure. In social science, theoretical concepts such as short-term memory are often used to explain differences in human behavior. Psychologists call these theoretical concepts hypothetical constructs or latent variables. They are theoretical psychological properties, attributes, processes or states that cannot be observed directly. The procedures or actions with which they measure these hypothetical constructs are called operational definitions.
What is a psychological test?
According to Cronbach, a psychological test is a systematic procedure for comparing the behavior of two or more people. This test must meet three conditions:
- the test must have behavioral samples;
- the behavioral samples must be collected in a systematic manner and;
- the purpose of the test must be to measure the behavior of two or more people (inter-individual differences).
It is also possible that we measure the behavior of an individual at different times, in which case we speak of intra-individual differences.
Different types of testing
You can distinguish between different tests in the field of content. Which type of answer is used (open or closed) and which methods are used in the measurement.
A distinction is also made between the different objectives of testing: the criterion referenced and norm referenced. Criterion referenced tests (also called domain referenced tests) are most common in situations where a statement must be made about a certain skill of a person. One pre-determined cutoff score is used to divide people into two groups: people whose score is higher than the cutoff score and people whose score is lower than the cutoff score.
Norm-referenced tests are mainly used to compare the scores of a person with scores from the norm group. Nowadays, it is difficult to make a distinction between the benchmark tests and the benchmark tests.
Another well-known distinction between tests is the distinction between the so-called speed tests (speed) and power tests. Speed tests are time-bound tests. It often happens that not all questions can be answered in a questionnaire. We look at how many questions you can answer correctly in the given time. Power tests are not time-bound tests. Here it is highly likely that one can answer all questions in a questionnaire. These questions often become more difficult and it is checked here how many questions people have answered correctly.
Finally, the difference between reflective or effect indicators and formative or causal indicators is briefly discussed. An example of reflective / effect indicators are scores on intelligence or personality tests. These scores are usually considered as a reflection, or consequence, of a person's intelligence level. There are formative / causal indicators against this. Socio-economic status (SES) can, for example, be quantified by combining different indicators such as income, education level, and occupation. In this case, the indicators are not caused by SES. In contrast, the indicators are, in part, what SES defines. In this book the focus is on test scores, derived from reflective / effect indicators, which is typical of most tests and measurements in psychology.
What is psychometrics?
With psychometrics, the focus is on the attributes of testing. Just as psychological tests are designed to measure psychological attributes of people, psychometry is the science where people are concerned with the attributes of psychological tests. There are three attributes that are important: the type of data (mainly scores), the reliability and validity of the psychological tests. Psychometrics is about the procedures with which test attributes are estimated and evaluated.
Psychometrics is based on two important foundations. The first foundation is the practice of psychological testing and measurement. The use of formal tests to measure skills of an individual (of any kind) goes back 2,000 years, or maybe even 4,000 years. Especially in the last 100 years there has been a huge increase in the number, type, and application of psychological tests. The second foundation is the development of static concepts and procedures. From the beginning of the nineteenth century, scientists became increasingly aware of the importance of static concepts and procedures. This led to an increase in knowledge about how quantitative data resulting from psychometric tests can be understood and analyzed. Pioneers in this field are Charles Spearman, Karl Pearson, and Francis Galton .
Francis Galton was obsessed with measurements, mainly the so-called 'anthropometry'. Anthropometry contains measurements of human characteristics such as the size of the head, the length of an arm and the physical strength of the body. These properties have, according to Galton, psychological characteristics. He called these measurements of mental traits 'psychometrics'. Galton was primarily interested in the ways in which people differ. Galton's point of view was known as differential psychology , or the study of individual differences.
Psychometrics is the collection of procedures that are used to measure variability in human behavior and subsequently combine these measurements into psychological phenomena. Psychometrics is a relatively young, but rapidly developing, scientific discipline.
What are the challenges in psychometrics?
Many sciences are very similar but behavioral science has its challenges.
One of those challenges is to try to identify and capture the important aspects of different types of human psychological attributes in a single number.
A second challenge is participant reactivity. When participants know that they are being tested and they know why, this in itself influences the responses of the participant. For example, if a participant knows that it is being tested whether he or she is a racist but does not want this to appear in the test, this influences his or her reactions. Examples of participant reactivity are demand characteristics (influenced by what the participant thinks is the goal of the researcher), social desirability (responding to the wishes of the outside world), and malingering (wanting to leave a bad impression).
A third challenge is that psychologists rely on so-called composite scores. This means that scores that have something in common are combined. For example, in a questionnaire with ten questions about extraversion, the scores on these questions are combined.
A fourth challenge in psychological measurement is the problem of score sensitivity. Sensitivity refers to the possibility of a measurement to distinguish meaningful dimensions. For example, a psychologist wants to know if a patient's mood has changed. But if the psychologist uses an instrument that is not sensitive enough to measure small changes, the psychologist may miss important changes.
The final challenge is the lack of attention to important information in psychometrics. Knowledge about psychometrics increases the chance of developments in testing. And test takers should at least use psychometrically good instruments.
These challenges should make us aware of the data collected through psychological measurements. For example, we must be aware of the fact that participant reactivity can influence the reactions of the participants in a test.
What is the purpose of measuring in psychology?
The theme that links the chapters of this book is related to the fact that the ability to identify and characterize psychological differences is the basis of all methods used to evaluate tests.
The purpose of measuring in psychology is to identify and quantify psychological differences that exist between people, over time or in different situations.
What is important when assigning numbers to psychological constructs? - Chapter 2
In psychological tests, grades are assigned to traits to show the difference between the traits of the different test subjects. Measuring is the assignment of a figure to objects or to characteristics of individual behavior according to a certain scale. Scaling is the way numbers are assigned to psychological traits.
What are variability and covariability? - Chapter 3
Variability (also called variance) is the difference within a set of test scores or between the values of a psychological trait. Inter-individual differences are differences that occur between people. Intra-individual differences are differences within one person at different times. Individual differences are very important in psychological tests. Reliability and validity of tests depend on the ability of a test to quantify differences between people. All research in psychology and all scientific applications of psychology depend on the ability of a test to measure individual differences. It is important to know that every area of scientific psychology depends on the existence and quantification of individual differences.
You can quantitatively display scores of a group of people or scores of one person at different times in a so-called distribution of scores. A distribution of scores is quantitative, because the differences between scores are expressed in figures. The difference between scores within a distribution is called the variability.
What is dimensionality and what is factor analysis? - Chapter 4
When we measure a physical or psychological trait of an object or person, we only measure one trait of object or person. However, you can investigate multiple questions/items that ultimately lead to a certain dimension/trait. These are called composite scores.
In this chapter, the concept of dimensionality wil be discussed. This is done on the basis of three fundamental questions, and associated relevant information from an exploratory (explanatory) factor analysis (EFA):
- How many dimensions does a test have?
- One-dimensional
- Two (+) dimensional
- Relevant information from EFA: eigenvalues, scree plot, factor loads etc.
- Are the dimensions correlated?
- Yes: type of scale = multidimensional with beaded dimensions
- No: type of scale = multidimensional with uncorrelated dimensions
- Relevant information from EFA: rotation method, interfactor correlations
- What is the psychological service of the dimensions?
- Factor analysis
- Relevant information from EFA: factor loadings.
What is reliability? - Chapter 5
Chapter 5 is about the reliability of a test. Reliability is the extent to which differences in the observed scores of the respondent concerned correspond with differences in his or her true scores. The smaller the difference, the more reliable.
How to empirically estimate the reliability? - Chapter 6
Test scores can be used to estimate reliability scores and to estimate the measurement error. In this chapter three methods are discussed for estimating reliability: (1) alternate forms of reliability (also known as a parallel test); (2) test-retest reliability; (3) internal consistency. This chapter also looks at the reliability of the difference scores used for other cognitive growth, symptom reduction, personality change, etc.
What is the importance of reliability? - Chapter 7
This chapter explains how reliability and measurement errors affect the results of behavioral research. Awareness of these effects is crucial for behavioral research.
What is validity? - Chapter 8
For more than 60 years, the following basic definition of validity was assumed: Validity is the extent to which a test measures what it is intended to measure. Although this definition has been used very much and still is, the concept of validity is presented a little too simply through this definition. A better definition would be that validity is the extent to which the interpretation of test scores for a specific purpose is supported by evidence and theory.
How to evaluate evidence for convergent and divergent validity? - Chapter 9
In the previous chapter we discussed the conceptual framework of validity, where we could identify five types of proof of validity. One of the types of evidence was convergent and divergent validity: the extent to which test scores have the "right" pattern of associations with other variables. This is discussed further in this chapter.
What types of response bias are there? - Chapter 10
Chapters 10 and 11 deal with threats to psychometric quality. Two types of threats are central here: reaction bias and test bias. Chapter 10 is about response bias. Test bias is discussed in chapter 11.
What types of test bias are there? - Chapter 11
In the previous chapter we discussed response bias, a common threat to the psychometric quality of tests. In this chapter we discuss the second major threat: test bias. Test bias arises when the true scores and the observed scores differ between two groups. Think of men and women as two groups. The emphasis of test bias is therefore on systematic differences between groups of respondents. Please note that the identification of differences between groups does not necessarily mean that there is also (test) bias; it may be that these differences are actually present in reality that way.
What is a confirmatory factor analysis? - Chapter 12
In chapters 4 and 8 we discussed the internal structure (i.e., dimensionality) of a psychological test. As we briefly introduced there, the internal structure of a test has to do with the number and nature of the psychological constructs that we measure with the items. One way to identify those constructs is through factor analysis. In this chapter, we will discuss factor analysis, and in particular confirmatory factor analysis (CFA).
What is the generalizability theory? - Chapter 13
The Generalizability Theory (G theory) helps us to distinguish the effects of multiple facets and then to use different measurement strategies. It is an ideal framework for complex measurement strategies in which several facets influence the measurement quality. This is a fundamental difference compared to the classical test theory (CTT), where different facets are not assumed.
What is the Item Response Theory (IRT) and which models are there? - Chapter 14
The Item Response Theory (IRT) is an alternative to the classical test theory (CTT). The IRT identifies and analyzes the measurements in behavioral sciences. The reaction of the individual to a certain test item is influenced by characteristics of the individual ( trait level ) and properties of the item (difficulty level).
- For a difficult item / question, someone needs a high ' trait level' to be able to give a correct answer.
- Conversely, with an easy item / question, someone with a low ' trait level' is enough to give a good answer.