validity & realibility

8/3/2019 Validity & Realibility

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ReliabilityThe consistency of scores obtained from oneinstrument to another or from the sameinstrument over different groups.

Test retestEquivalency

Inter rater

Internal consistency

Split half


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Test retest reliability Method for testing the same subject at

a later date, ensuring that there is acorrelation between the results.

An educational test taken after amonth should yield the same resultsas the original.


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Equivalency reliability method which two items measure

identical concepts at an identical levelof difficulty.

is determined by relating two sets oftest scores to one another to highlightthe degree of relationship.


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Inter-rater reliability Method use two or more independentjudges score the test.

The scores are then compared to

determine the consistency of the raterestimates.

One way to test inter rater reliability is

to have each rater assign each testitem a score.


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Internal consistencyreliability Method used to judges the consistency of

result across items on the same test.

Compare test items that measure the same

construct to determine the tests internalconsistency.

Example, when a question is very similar toanother test question, it may indicate that

the two questions are being used togauge(measure) reliability.


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Split-half reliability A measure of consistency where a test

is split into two and the scores foreach half of the test is compared with

one another. If the test is consistent, it leads the

experimental to believe that it is most

likely measuring the same thing.


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Factors affecting

reliability Test length - the longer a test is, the more

reliable Speed - when a test is a speed test, reliability

can be problematic. Group homogeneity - the more heterogeneous

the group of students who take the test, the morereliable the measure will be.

Item difficulty - reliability will be low if a test is soeasy or difficult.

Objectivity - objectively scored tests show a

higher reliability than subjectively scored tests. Test-retest interval -the shorter the time interval

between two administrations of a test, the higherthe reliability will be.

Variation with the testing situation. Errors in the

testing situation can cause test scores to vary.


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Relationship between

validity and reliability Reliability is an essential component

of validity but on its own, is notsufficient measured of validity.

A test can be reliable but not valid,whereas a test cannot be valid yetunreliable.


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Validity Validityrefers to the accuracy of an assessment --

whether or not it measures what it is supposed tomeasure. Even if a test is reliable, it may not provide avalid measure. Lets imagine a bathroom scale thatconsistently tells you that you weigh 130 pounds.

The reliability (consistency) of this scale is very good,but it is not accurate (valid) because you actually weigh145 pounds (perhaps you re-set the scale in a weakmoment)

Since teachers, parents, and school districts makedecisions about students based on assessments (suchas grades, promotions, and graduation), the validityinferred from the assessments is essential -- even morecrucial than the reliability.


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Example 1 :


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Example 2:


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Type of Validity Definition Example

Content The extent to which the

content of the test matches

the instructional objectives.

A semester or quarter exam

that only includes content

covered during the last six

weeks is not a valid measureof the course's overall

objectives -- it has very low

content validity.

Criterion The extent to which scores on

the test are in agreement with(concurrent validity) or predict

(predictive validity) an external

criterion.

If the end-of-year math tests

in 4th grade correlate highlywith the statewide math tests,

they would have high

concurrent validity.

Construct The extent to which an

assessment corresponds toother variables, as predicted

by some rationale or theory.

If you can correctly

hypothesize that the studentswill perform differently on a

reading test than English-

speaking students (because

of theory), the assessment

may have construct validity.


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Factors thatinfluences

validityassessment

Nature ofthe group

Moderatorvariables

Criterion-predictor

relationship

Consistency of the validitycoefficient for subgroups whichdiffer in any characteristic (e. g.age, gender, educational level,

etc, )

There must be a linearrelationship between predictor

and criterion.

Variables like age, gender,personality characteristics mayhelp to predict performance forparticular variables only

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