Psychology Module 5: Reliability

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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?

  • Consistency in measurement (correct)
  • Variability in measurement
  • Validity of measurement
  • Random errors in measurement

Test-retest reliability is used to estimate the stability of a test over time.

True (A)

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.

<p>administrations</p> Signup and view all the answers

What is one of the advantages of developing alternate or parallel forms of tests?

<p>Minimizes the effect of memory for the content of a previously administered form of the test (A)</p> Signup and view all the answers

What method of estimating reliability refers to the degree of correlation among all the items on a scale?

<p>Inter-item consistency</p> Signup and view all the answers

What is the purpose of the reliability coefficient?

<p>To measure the consistency and dependability of a test's results over time.</p> Signup and view all the answers

The _________ formula allows a test developer to estimate internal consistency reliability from a correlation of two halves of a test.

<p>Spearman-Brown</p> Signup and view all the answers

Coefficient alpha is only suitable for tests with dichotomous items.

<p>False (B)</p> Signup and view all the answers

Which characteristics influence the nature of a test? Select all that apply.

<p>Homogeneity of test items (A), Dynamic versus static characteristics (B), Speed tests versus power tests (C), Criterion-referenced tests (D), Range of test scores (E)</p> Signup and view all the answers

What is the standard error of measurement (SEM) used for?

<p>To estimate the amount of error inherent in an observed test score.</p> Signup and view all the answers

What is the best estimate available of the individual's true score on a test?

<p>Test score already obtained</p> Signup and view all the answers

What is the standard error of measurement used for?

<p>Interpretation of individual test scores</p> Signup and view all the answers

What is a confidence interval in the context of test scores?

<p>A range or band of test scores likely to contain the true score</p> Signup and view all the answers

What does the standard error of the difference between two scores help determine?

<p>How large a difference should be before it is considered statistically significant</p> Signup and view all the answers

What must be considered when comparing scores achieved on different tests?

<p>Converting the scores to the same scale</p> Signup and view all the answers

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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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