IHE Report - Institute of Health Economics

Reliability: A measure is reliable when it yields the same score after repeatedmeasurements in stable patients. Reliability can be assessed in differentways: intra-rater (test-retest), inter-rater and internal consistency. Test-retestis assessed when under the identical conditions the same rater repeats themeasure. Inter-rater reliability refers to the measurement that is made at thesame point in time by two or more raters and yields the same score. Internalconsistency among the items in a questionnaire refers to the relationshipamong the items administered at the same point in time, and is oftenmeasured by Cronbach’s alpha.Validity: A HRQL instrument is valid when it measures what it is supposed tomeasure. There are four types of validity: face, content, construct and criterionvalidity. Face validity is the extent to which the users and respondents findthe items included in the measure to be relevant. Content validity refers to therelevance of the items and domains included in the measure. Construct validityrefers to the extent to which a particular measure relates to other measuresin a way that is consistent with the theoretically derived hypotheses relatedto concepts that are being measured. Another approach is to compare scoresfor known groups either cross-sectionally or longitudinally. The assessmentof construct validity involves the specification of a priori hypotheses and thetesting of those hypotheses. Finally, criterion validity involves the assessmentof the relationship between the test measure and the criterion or gold standard.In general, in the field of HRQL, there is no gold standard and thus criterionvalidity is of limited use except for the evaluation of predictive validity.Responsiveness: A measure is responsive when it is able to capture changein a patient’s condition over time when it occurs. Some investigators use theterm longitudinal construct validity instead.Usefulness: Usefulness refers to the ability of the measure to influence decisionmaking including the management of individual patients, formulation of clinicalpolicy, and resource allocation. Does the use of the measure matter?Interpretability: Interpretability refers to the ability to assign meaning tothe scores yielded by the measure (quantitative or qualitative). Effectiveinterpretation of the results involves the accumulation of experience andevidence. Interpretation involves an idea of the magnitude of differencesor changes that are clinically important.What is the clinically important difference?“Is the smallest difference which patients perceive as beneficial and whichwould mandate, in the absence of troublesome side effects and excessive cost,a change in the patient’s management” (Jaeschke et al. 1989). At all levels, oneneeds to understand and explain HRQL differences in ways that are relevantto the health care decision at hand and to people involved in that decision.(Osoba D. 1999).5The Importance of Measuring Health-related Quality of Life