What Is Test Reliability/Precision?

Chapter 5

What Is Reliability/Precision?

Measurement error: variations in measurement using a reliable instrument.

Reliable test: is one we can trust to measure each person in approximately the same way every time it is used.

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Classical Test Theory

True score (T): is a measure of the amount of the attribute that the test is designed to measure.

Random error: The second part of an observed test score consists of random errors that occur anytime a person takes a test (E).

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Classical Test Theory

True Score

Random Error

Systematic Error

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Classical Test Theory

The Formal Relationship Between Reliability/Precision and Random Measurement Error

Parallel

Reliability coefficient: the correlation between the two sets of test scores

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Three Categories of Reliability Coefficients

Test–retest method: a test developer gives the same test to the same group of test takers on two different occasions.

Correlation: the scores from the first and second administrations are then compared.

Practice effects: occur when test takers benefit from taking the test the first time (practice), which enables them to solve problems more quickly and correctly the second time.

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Three Categories of Reliability Coefficients

Alternate-Forms Method

Alternate forms: the test developer creates two different forms of the test.

Order effects: changes in test scores resulting from the order in which the tests were taken.

Parallel forms: describes different forms of the same test.

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Three Categories of Reliability Coefficients

Internal consistency method: is a measure of how related the items (or groups of items) on the test are to one another.

Split-half method: is to divide the test into halves and then compare the set of individual test scores on the first half with the set of individual test scores on the second half.

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Three Categories of Reliability Coefficients

Homogeneous tests: measuring only one trait or characteristic.

Heterogeneous tests: measuring more than one trait or characteristic.

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Three Categories of Reliability Coefficients

Scorer Reliability

Scorer reliability or interscorer agreement: the amount of consistency among scorers’ judgments

Intrascorer reliability: whether each clinician was consistent in the way he or she assigned scores from test to test.

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The Reliability Coefficient

Adjusting Split-Half Reliability Estimates

Other Methods of Calculating Internal Consistency

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The Reliability Coefficient

Calculating Scorer Reliability/Precision and Agreement

Interrater agreement: an index of how consistently the scorers rate or make decisions.

Intrarater agreement: when one scorer makes judgments, the researcher also wants assurance that the scorer makes consistent judgments across all tests.

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Interpreting Reliability Coefficients

Calculating the Standard Error of Measurement

Standard error of measurement (SEM): is an estimate of how much the individual’s observed test score (X) might differ from the individual’s true test score (T).

Interpreting the Standard Error of Measurement

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Interpreting Reliability Coefficients

Confidence Intervals

Confidence interval–a range of scores that we feel confident will include the test taker’s true score.

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Factors That Influence Reliability

Test Length

Homogeneity

Test–Retest Interval

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Factors That Influence Reliability

Test Administration

Scoring

Cooperation of Test Takers

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Generalizability Theory

Generalizability theory: an approach to estimating reliability/precision.

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