Table 1 Definitions of the measurement properties and their quality criteria
Measurement property | Description a | Quality criteria for measurement properties b | ||
|---|---|---|---|---|
Validity | Content validity | To which degree the construct assesses whether the items are relevant for the construct to be measured | +: The target population considers all items in the instrument to be relevant AND to be complete | |
?: No target population involvement | ||||
-: The target population considers the items of the instrument irrelevant OR incomplete | ||||
Construct validity | Structural validity | To which degree the scores of an instrument are an adequate reflection of the dimensionality | +: Factors should explain at least 50% of the variance | |
?: Explained variance not mentioned | ||||
-: Factors explain < 50% of the variance | ||||
Hypothesizes testing | To which extent the scores of the instrument are consistent with the theoretically derived hypotheses | +: Correlation with an instrument measuring the same construct ≥ 0.50 or at least 75% of the results are in accordance with the hypotheses AND correlation with related constructs is higher than with unrelated constructs | ||
?: Solely correlations determined with unrelated constructs | ||||
-: Correlations with an instrument measuring the same construct <0.50 OR <75% of the results are in accordance with the hypotheses OR correlation with related constructs is lower than with unrelated constructs | ||||
Cross-cultural validity | To which extend the items are an adequate reflection of the original version after translation or culturally adaptation. | +: no important DIF between language versions | ||
?: DIF not assessed | ||||
-: Important DIF found between language versions | ||||
Criterion validity | To what degree the scores of the instrument are an adequate reflection of a ‘gold standard’. The gold standard should fit the purpose of the assessed instrument. | +: Convincing arguments that gold standard is ‘’gold” AND correlations with gold standard ≥0.70 | ||
?: No convincing argument that gold standard is ‘’gold” OR doubtful design or method | ||||
-: Despite adequate design and method, correlation is < 0.70 | ||||
Reliability | Reliability | The proportion of the total variance in the measurements which is because of ‘’true” differences among patients | +: ICC/weighted kappa ≥ 0.70 OR Pearson’s r ≥ 0.80 | |
?: Neither ICC/weighted kappa, nor Pearson’s r determined | ||||
-: ICC/weighted kappa <0.70 OR Pearson’s r < 0.80 | ||||
Internal consistency | The extent to which items in a sub(scale) are inter correlated, thus measuring the same construct | +: Cronbach’s α (s) ≥ 0.70 | ||
?: Cronbach’s α not determined | ||||
-: Cronbach’s α < 0.70 | ||||
Measurement error | The systematic and random error of a patient’s score that is not attributed to true changes in the construct to be measured | +:MIC <SDC OR MIC outside the LOA OR convincing arguments that agreement is acceptable | ||
?: Doubtful design or method OR MIC not defined AND no convincing arguments that agreement is acceptable | ||||
-: MIC≥ SDC OR MIC equals or inside LOA, despite adequate design and method | ||||
Responsiveness | The ability of the instrument to detect change over time | +: Correlation with an instrument measuring the same construct ≥ 0.50 OR at least 75% of the results are in accordance with the hypotheses OR AUC ≥ 0.70 AND correlation with related constructs is higher than with unrelated constructs | ||
?: Solely correlations determined with unrelated constructs | ||||
-: Correlation with an instrument measuring the same construct <0.50 OR <75% of the results are in accordance with the hypotheses or AUC <0.70 OR correlation with related constructs is lower than with unrelated constructs. | ||||