Psychometric properties of the Vertigo symptom scale - Short form.
BACKGROUND
The aim of the study was to examine the psychometric properties of the Vertigo symptom scale - short form (VSS-SF), a condition-specific measure of dizziness, following translation of the scale into Norwegian.


METHODS
A cross-sectional survey design was used to examine the factor structure, internal consistency and discriminative ability (sample I, n = 503). A cross-sectional pre-intervention design was used to examine the construct validity (sample II, n = 36) of the measure and a test-retest design was used to examine reliability (sub-sample of sample II, n = 28).


RESULTS
The scree plot indicated a two factor structure accounting respectively for 41% and 12% of the variance prior to rotation. The factors were related to vertigo-balance (VSS-V) and autonomic-anxiety (VSS-A). Twelve of the items loaded clearly on either of the two dimensions, while three items cross-loaded. Internal consistency of the VSS-SF was high (alpha = 0.90). Construct validity was indicated by correlation between path length registered by platform posturography and the VSS-V (r = 0.52), but not with the VSS-A. The ability to discriminate between dizzy and not dizzy patients was excellent for the VSS-SF and sub-dimension VSS-V (area under the curve 0.87 and 0.91, respectively), and acceptable for the sub-dimension VSS-A (area under the curve 0.77). High test-retest reliability was demonstrated (ICC VSS-SF: 0.88, VSS-V: 0.90, VSS-A: 0.90) and no systematic change was observed in the scores from test to retest after 2 days.


CONCLUSIONS
Using a Norwegian translated version of the VSS-SF, this is the first study to provide evidence of the construct validity of this instrument demonstrating a stable two factor structure of the scale, and the identified sub-dimensions of dizziness were related to vertigo-balance and autonomic-anxiety, respectively. Evidence regarding a physical construct underlying the vertigo-balance sub-scale was provided. Satisfactory internal consistency was indicated, and the discriminative ability of the instruments was demonstrated. The instrument showed satisfactory test-retest reliability.
Wilhelmsen
Kjersti
K
Department of Public Health and Primary Health Care, Section for Physiotherapy Science, University of Bergen, Norway.|National Centre for Vestibular Disorders, Department of Otorhinolaryngology/Head and Neck Surgery, Haukeland University Hospital, Bergen, Norway.
Strand
Liv Inger
LI
Department of Public Health and Primary Health Care, Section for Physiotherapy Science, University of Bergen, Norway.|Department of Physical Therapy, Haukeland University Hospital, Bergen, Norway.
Nordahl
Stein Helge G
SHG
National Centre for Vestibular Disorders, Department of Otorhinolaryngology/Head and Neck Surgery, Haukeland University Hospital, Bergen, Norway.
Eide
Geir Egil
GE
Centre for Clinical Research, Haukeland University Hospital, and Department of Public Health and Primary Health Care, University of Bergen, Norway.
Ljunggren
Anne Elisabeth
AE
Department of Public Health and Primary Health Care, Section for Physiotherapy Science, University of Bergen, Norway.