Stability or consistency of measurement. Reliability studies in PDD often examine the rate of decision agreement among examiners on polygraph test charts. Interrater (between rater) reliability denotes agreement among examiners, whereas intrarater (within rater) agreement (test-retest reliability) pertains to an examiner agreement with his or her own decisions when evaluating the charts on different occasions. Reliability is not the same as validity, which means accuracy. A technique cannot be more valid than it is reliable since reliability constrains validity.