Questions and Answers
What is a reliability coefficient in psychometrics?
An index of reliability, a proportion that indicates the ratio between the true score variance on a test and the total variance.
What does the term reliability refer to?
Test-retest reliability is used to estimate the stability of a test over time.
True
Test-retest reliability is an estimate of reliability obtained by correlating pairs of scores from the same people on two different __________ of the same test.
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What is one of the advantages of developing alternate or parallel forms of tests?
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What method of estimating reliability refers to the degree of correlation among all the items on a scale?
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What is the purpose of the reliability coefficient?
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The _________ formula allows a test developer to estimate internal consistency reliability from a correlation of two halves of a test.
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Coefficient alpha is only suitable for tests with dichotomous items.
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Which characteristics influence the nature of a test? Select all that apply.
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What is the standard error of measurement (SEM) used for?
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What is the best estimate available of the individual's true score on a test?
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What is the standard error of measurement used for?
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What is a confidence interval in the context of test scores?
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What does the standard error of the difference between two scores help determine?
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What must be considered when comparing scores achieved on different tests?
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Study Notes
Reliability
- Reliability refers to consistency in measurement, and is a crucial aspect of psychological assessment.
Concept of Reliability
- In the language of psychometrics, reliability is an index of reliability, which is a proportion that indicates the ratio between the true score variance on a test and the total variance.
- A score on an ability test is presumed to reflect not only the test-taker's true score on the ability being measured but also error.
Sources of Error Variance
- Test construction: item sampling or content sampling can be a source of error variance.
- Test administration: factors such as room temperature, lighting, and ventilation can influence the test-taker's attention or motivation.
- Examiner-related variables: the examiner's physical appearance, demeanor, and nonverbal gestures can be sources of error variance.
- Test scoring and interpretation: scorer differences can be a source of error variance, especially in subjective scoring.
Reliability Estimates
- Test-Retest Reliability Estimates: a way of estimating the reliability of a measuring instrument is by using the same instrument to measure the same thing at two points in time.
- Parallel-Forms and Alternate-Forms Reliability Estimates: the degree of the relationship between various forms of a test can be evaluated by means of an alternate-forms or parallel-forms coefficient of reliability.
Key Concepts
- True score variance refers to the proportion of the total variance attributed to true variance.
- Error variance refers to the proportion of the total variance attributed to irrelevant, random sources.
- Systematic source of error does not affect score consistency.
- Variance from true differences is true variance, and variance from irrelevant, random sources is error variance.### Reliability Coefficients
- Item sampling is an additional source of error variance in computing alternate- or parallel-forms reliability coefficient.
- Developing alternate forms of tests can be time-consuming and expensive, but it minimizes the effect of memory for the content of a previously administered form of the test.
Internal Consistency Estimates of Reliability
- Internal consistency estimate of reliability is an evaluation of the internal consistency of the test items.
- Methods of obtaining internal consistency estimates of reliability include split-half estimates and Kuder-Richardson formulas.
Split-Half Reliability Estimates
- Split-half reliability entails dividing the test into equivalent halves, correlating scores on the two halves, and adjusting using the Spearman-Brown formula.
- Ways to split a test include randomly assigning items to one or the other half, assigning odd-numbered items to one half and even-numbered items to the other half, or dividing the test by content.
The Spearman-Brown Formula
- The Spearman-Brown formula allows a test developer to estimate internal consistency reliability from a correlation of two halves of a test.
- The formula is used to estimate the reliability of a whole test from the reliability of one half of a test.
Other Methods of Estimating Internal Consistency
- Inter-item consistency refers to the degree of correlation among all the items on a scale.
- Tests are said to be homogeneous if they contain items that measure a single trait, and heterogeneous if they measure more than one trait.
The Kuder-Richardson Formulas
- The Kuder-Richardson formulas were developed by G. Frederic Kuder and M.W. Richardson to estimate reliability.
- KR-20 is widely used for estimating inter-item consistency of dichotomous items, and KR-21 is an approximation of KR-20.
Coefficient Alpha
- Coefficient alpha is the mean of all possible split-half correlations, corrected by the Spearman-Brown formula.
- It is appropriate for use on tests containing nondichotomous items and is widely used as a measure of reliability.
- Coefficient alpha is the preferred statistic for obtaining an estimate of internal consistency reliability.
Measures of Inter-Scorer Reliability
- Inter-scorer reliability is the degree of agreement or consistency between two or more scorers with regard to a particular measure.
- Measures of inter-scorer reliability include calculating a coefficient of correlation, referred to as a coefficient of inter-scorer reliability.
Using and Interpreting a Coefficient of Reliability
- There are three approaches to the estimation of reliability: test-retest, alternate or parallel forms, and internal consistency estimates.
- A reliability index published in a test manual may not be applicable to a new group of testtakers, and measures of reliability are subject to error.### Purpose of Reliability Coefficient
- The reliability coefficient is a measure of how high a test score should be, depending on the purpose and importance of the decisions made based on the scores.
- A test designed for multiple administrations over time should demonstrate reliability across time, and an estimate of test-retest reliability is desirable.
Nature of the Test
- The nature of the test influences the choice of reliability coefficient.
- Considerations include:
- Homogeneity or heterogeneity of test items
- Dynamic or static characteristics being measured
- Restricted or inflated range of test scores
- Speed or power test
- Criterion-referenced test
Homogeneity vs. Heterogeneity
- Homogeneous test items: functionally uniform throughout, measuring one factor or ability, expected to have high internal consistency.
- Heterogeneous test items: not uniformly measuring one factor or ability, internal consistency may be low.
Dynamic vs. Static Characteristics
- Dynamic characteristics: ever-changing traits, states, or abilities, best measured by internal consistency.
- Static characteristics: relatively unchanging traits, states, or abilities, best measured by test-retest or alternate-forms reliability.
Restriction or Inflation of Range
- Restricted range of test scores: correlation coefficient tends to be lower.
- Inflated range of test scores: correlation coefficient tends to be higher.
Speed vs. Power Tests
- Speed tests: uniformly low difficulty, time limits allow test-takers to complete all items, reliability estimated using test-retest, alternate-forms, or split-half reliability.
- Power tests: high difficulty, time limits allow test-takers to attempt all items, reliability estimated using test-retest, alternate-forms, or split-half reliability.
Criterion-Referenced Tests
- Designed to measure mastery of specific skills or knowledge.
- Scores interpreted in pass-fail terms, used for diagnostic and remedial purposes.
Alternatives to True Score Model
- Domain sampling theory: estimates the extent to which specific sources of variation contribute to the test score.
- Generalizability theory: examines how generalizable scores are across different testing situations.
- Item response theory: models the probability of a person's performance based on their ability.
Reliability and Individual Scores
- Standard error of measurement (SEM): estimates the precision of an observed test score, inverse relationship with reliability.
- SEM used to estimate the true score and establish a confidence interval.
Standard Error of the Difference between Two Scores
- Used to compare scores between tests, individuals, or both.
- Essential to convert scores to the same scale when comparing across tests.
- Formula for standard error of the difference between two scores: √(SEM1^2 + SEM2^2).
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Description
This quiz covers the concept of reliability in the context of psychology. It assesses students' understanding of reliability in psychology research and its applications.
