CONVERGENT CONSTRUCT VALIDITY AND TEST-RETEST RELIABILITY OF THE GERMAN NPQ-R

C. Schuster-Amft^1,2,3, S. Chételat⁴, M. Stark⁴, S. Schädler⁵, E.-Y. Gerber^6,1, F. Behrendt^1,2, L. Bonati^1,7,8

¹Reha Rheinfelden, Research Department, Rheinfelden, Switzerland, ²Bern University of Applied Sciences, Department of Engineering and Information Technology, Burgdorf, Switzerland, ³University of Basel, Department for Sport, Exercise and Health, Basel, Switzerland, ⁴Zurich University of Applied Sciences, Institute for Physiotherapy, Winterthur, Switzerland, ⁵Private Practice, Sumiswald, Switzerland, ⁶University of Basel, Department of Psychology, Basel, Switzerland, ⁷University of Basel, Department of Neurology, Basel, Switzerland, ⁸University of Basel, Department of Clinical Research, Basel, Switzerland

Background: Persistent Postural-Perceptual Dizziness (PPPD) is considered the second most common form of vertigo, after benign paroxysmal positional vertigo. The Japanese Niigata PPPD Questionnaire was translated into German and revised to include the perspective of patients and experts and therefore improve content validity.

Purpose: The aim was to examine convergent construct validity and test-retest reliability of the NPQ-R.

Methods: Patients with a diagnosis of PPPD filled in patient-related outcome measures for dizziness and potentially related constructs: NPQ-R, Dizziness Handicap Inventory, Vertigo Symptom Scale, Hospital Anxiety and Depression Scale, Activities-specific Balance Confidence Scale, SF-36). A cross-sectional design was used to assess internal consistency (Cronbach’s α) and convergent validity (Spearman’s rank correlation coefficient r) and a longitudinal design was used to examine test-retest reliability (two-way mixed effect model, Intraclass Correlation Coefficent, ICC).

Results: 68 patients (age 55.4±17.9 years; 38 females; duration of dizziness: 51.3±69.3 months) were analysed. Descriptive-statistical item analysis revealed the retention of all newly added items of the NPQ-R. Acceptable internal consistency was found for each subscales: upright posture (α=0.76), movement (α=0.75), visual (α=0.86), associated symptoms (α=0.71), symptom behavior (α=0.72). Test-retest reliability was satisfactory with ICC=0.85 (CI 0.78-0.89) and the smallest detectable change was 21 points. Correlations between the NPQ-R and disease-specific measurement instruments was high (r=0.66-0.77), between the NPQ-R and anxiety-specific conditions moderate to high (r=0.48-0.55). A correlation from 0.22 to 0.65 was shown between the NPQ-R and self-report measures of general quality of life.

Conclusions: The NPQ-R demonstrated preliminary satisfactory convergent construct validity and test-retest reliability for the German version including 19 items and 5 subscales.

Implications: The scale development must be further investigated regarding parsimony and dimensionality using both structure-seeking and structure-checking procedures, respectively with factor analytic methods (EFA and CFA).

Funding acknowledgements: This study was not funded.

Keywords:
Persistent postural-perceptual dizziness (PPPD)
Patient-reported outcome measure
Test-retest reliability, construct validity

Topics:
Neurology
Disability & rehabilitation
Mental health

Did this work require ethics approval? Yes

Institution: Reha Rheinfelden

Committee: Ethics Committee of Northwest- and Central Switzerland (EKNZ)

Ethics number: Req-2021-00974