Page 122 - Bladder Dysfunction in the Context of the Bladder-Brain Connection - Ilse Groenendijk.pdf

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Chapter 6
Measurement properties
Content validity
The content validity was assessed during the linguistic validation by patient and research- ers (IG, BB and JS). Researchers subjectively evaluated the correspondence between the clinical symptoms of OAB and the questions. Patients reported on the formulation of the questions and clarity of the questions during the face-to-face evaluation.
Internal consistency
By assessing the correlation between different items within the questionnaire, the internal consistency is examined, demonstrating whether the items measure the same underlying construct. The Cronbach’s alpha was calculated for the two subscales of the OAB-q SF. A Cronbach’s alpha between 0.70 and 0.95 was considered to reflect adequate internal consistency.15
Reproducibility
The reproducibility is the degree to which repeated measurements in the test-retest pe- riod provide similar answers. When testing the reproducibility, a distinction between the reliability and agreement is made.15,16 Reliability is determined by the degree to which patients can be differentiated from each other, despite the measurement error. This was expressed by the intraclass correlation coefficient (ICC) for agreement, scores over 0.70 are acceptable. Furthermore, the agreement indicates the measurement error which is the similarity in scores rated on separate occasions. The limits of agreement (LOA) were expressed as the mean change in scores of repeated measurements ±1.96 X standard deviation of the changes.16,17
Criterion validity
The criterion validity, i.e. the extent to which the OAB-q SF questionnaire scores relate to a gold standard, is determined with the Pearson’s correlation coefficient (range -1 to 1) in case of a linear association and when a linear association is not seen, the Spearman correlation coefficient. For OAB, a gold standard does not exist, and instead the UDI-6 and the ICIQ-OAB (Q and BS) served as such.
Construct validity
Predefined hypotheses about the relation of the OAB-q SF to other instruments were tested. The construct validity is considered adequate when at least 75% of the results of predefined hypotheses are in accordance.15 The following hypotheses were formulated: 1. The reference group will have lower OAB-q SF symptom bother scores and higher
OAB-q SF HRQOL scores than the patient group.