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Lecture 7

HRS 610 Lecture 7: Lecture 7
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9 Pages
35 Views
Fall 2016

Department
HRS - HRS-Human Rehab Services
Course Code
HRS 610
Professor
Bezyak
Lecture
7

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1. Reliability
Reliability
oThe degree to which tests scores are consistent over repeated
applications of a measurement procedure and hence are
inferred to be dependable and repeatable.
oFrom the perspective of classical test theory, an examinee's
obtained test score (X) is composed of two components: a true
score component (T) and an error component (E):
X=T+E
oThe true score component reflects the examinee's status with
regard to the attribute that is measured by the test if tested
under perfect conditions.
oThe error component represents measurement error because
life is not perfect.
oMeasurement error is random error. It is due to factors that are
irrelevant to what is being measured by the test and have an
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unpredictable (unsystematic) effect on an examinee's test score.
Measurement error is assumed to be randomly distributed.
oThe score you obtain on a test is likely due to the knowledge you
have about the topics addressed by exam items (T) and the
effects of random factors (E). Random factors include the way
test items are written and any alterations in anxiety, attention,
or motivation you experience while taking the test.
oWhenever we administer a test to examinees, we would like to
know how much of the scores reflects "truth" and how much
reflects error.
oIt is a measure of reliability that provides an estimate of the
proportion of true score that is present in the person’s actual
score.
oWhen a test is reliable it provides dependable, consistent
results, and for this reason the term consistency is often given as
a synonym for reliability
Reliability Coefficient
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oMost methods for estimating reliability produce a reliability
coefficient, which is a correlation coefficient that ranges in value
from 0.0 to + 1.0.
oWhen a test's reliability coefficient is 0.0, all variability in
obtained test scores is due to measurement error.
oConversely, when a test's reliability coefficient is + 1.0, all
variability in scores reflects true score variability.
oThe reliability coefficient is symbolized with the letter r.
oRegardless of the method used to calculate a reliability
coefficient, the coefficient is interpreted directly as the
proportion of variability in obtained test scores that reflects true
score variability.
For example, a reliability coefficient of .84 indicates that
84% of variability in scores is due to true score differences
among examinees, while the remaining 16% (1.00 - .84) is
due to measurement error.
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Description
1. Reliability  Reliability o The degree to which tests scores are consistent over repeated applications of a measurement procedure and hence are inferred to be dependable and repeatable. o From the perspective of classical test theory, an examinee's obtained test score (X) is composed of two components: a true score component (T) and an error component (E):  X=T+E o The true score component reflects the examinee's status with regard to the attribute that is measured by the test if tested under perfect conditions. o The error component represents measurement error because life is not perfect. o Measurement error is random error. It is due to factors that are irrelevant to what is being measured by the test and have an unpredictable (unsystematic) effect on an examinee's test score. Measurement error is assumed to be randomly distributed. o The score you obtain on a test is likely due to the knowledge you have about the topics addressed by exam items (T) and the effects of random factors (E). Random factors include the way test items are written and any alterations in anxiety, attention, or motivation you experience while taking the test. o Whenever we administer a test to examinees, we would like to know how much of the scores reflects "truth" and how much reflects error. o It is a measure of reliability that provides an estimate of the proportion of true score that is present in the person’s actual score. o When a test is reliable it provides dependable, consistent results, and for this reason the term consistency is often given as a synonym for reliability  Reliability Coefficient o Most methods for estimating reliability produce a reliability coefficient, which is a correlation coefficient that ranges in value from 0.0 to + 1.0. o When a test's reliability coefficient is 0.0, all variability in obtained test scores is due to measurement error. o Conversely, when a test's reliability coefficient is + 1.0, all variability in scores reflects true score variability. o The reliability coefficient is symbolized with the letter r. o Regardless of the method used to calculate a reliability coefficient, the coefficient is interpreted directly as the proportion of variability in obtained test scores that reflects true score variability.  For example, a reliability coefficient of .84 indicates that 84% of variability in scores is due to true score differences among examinees, while the remaining 16% (1.00 - .84) is due to measurement error. o Remember a reliability coefficient does not provide any information about what is actually being measured by a test. o A reliability coefficient only indicates whether the attribute measured by the test is being assessed in a consistent, precise way. o Whether the test is actually assessing what it was designed to measure is addressed by an analysis of the test's validity.  Types of Reliability o The selection of a method for estimating reliability depends on the nature of the test. o Each method not only entails different procedures, but it is also affected by different sources of error. For many tests, more than one method should be used. o Test-Retest Reliability  Test-retest method for estimating reliability involves administering the same test to the same group of examinees on two different occasions and correlating the two sets of scores.  When using this method the reliability coeffici
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