Definitions
Reliability: The degree to which a measure of
the same object would produce the same value on repeated measurements.
Validity: The degree to which a measure
accurately reflects the underlying concept.
(The degree to which a measure actually measures what it is supposed
to.)
Relationship among
Concepts, Measurement, Reliability, and Validity
Measured
value = True value of Concept + Systematic error + Random error
Threat to Validity Threat to Reliability
Bull’s Eye Depiction of Reliability and Validity