Reliability vs. ValidityReliability vs. Validity

Reliability vs. ValidityReliability vs. Validity

ReliabilityReliability the consistency of your the consistency of your

measurement, or the measurement, or the degree to which an degree to which an instrument measures the instrument measures the same way each time it is same way each time it is used under the same used under the same condition with the same condition with the same subjects. subjects.

Test-retestTest-retest Internal consistencyInternal consistency

ValidityValidity the strength of our the strength of our

conclusions, inferences conclusions, inferences or propositions. Does it or propositions. Does it measure what it is measure what it is intended to measure?intended to measure?

ContentContent CriterionCriterion ConstructConstruct

ValidityValidityType of Type of validityvalidity

DefinitionDefinition Example/ Non exampleExample/ Non example

ContentContent The extent to which The extent to which the content of the test the content of the test matches the matches the instructional instructional objectives.objectives.

A semester or quarter exam that only A semester or quarter exam that only includes content covered during the last includes content covered during the last six weeks is not a valid measure of the six weeks is not a valid measure of the course's overall objectives -- it has very course's overall objectives -- it has very low content validity.low content validity.

CriterionCriterion The extent to which The extent to which scores on the test are scores on the test are in agreement with in agreement with (concurrent validity) or (concurrent validity) or predict (predictive predict (predictive validity) an external validity) an external criterion.criterion.

If the end-of-year math tests in 4th grade If the end-of-year math tests in 4th grade correlate highly with the statewide math correlate highly with the statewide math tests, they would have high concurrent tests, they would have high concurrent validity.validity.

ConstructConstruct The extent to which The extent to which an assessment an assessment corresponds to other corresponds to other variables, as variables, as predicted by some predicted by some rationale or theory.rationale or theory.

If you can correctly hypothesize that ESL If you can correctly hypothesize that ESL students will perform differently on a students will perform differently on a reading test than English-speaking reading test than English-speaking students (because of theory), the students (because of theory), the assessment may have construct validity. assessment may have construct validity.