The reliability of the Vestibular Autorotation Test (VAT) in patients with dizziness.

Objective: To establish intrarater and interrater reliability of the Vestibular Autorotation Test (VAT) (Western Systems Research Inc., Pasadena, CA) in a clinical sample of individuals reporting dizziness.

Study Design: Ninety-eight patients with reports of dizziness referred for vestibular function testing performed repeated trials of horizontal VAT. A subsample of 49 individuals repeated the test for a second rater.

Results: Approximately 66% of subjects were unable to meet the performance criterion of six consecutive trials where data was displayed at frequencies > or =3.9 Hz with coherence values held constant trial to trial. There was a good level of intrarater reliability for gain independent of the effects of practice (intraclass correlation coefficient [ICC] = 0.78 [95% confidence interval [CI]: 0.69-0.87] to 0.95 [(95% CI: 0.93-0.97]). A significant difference in intrarater reliability was found when the first three trials were compared to the last three trials for phase (ICC ranged from 0.04 [95% CI: 0.00-0.31] to 0.96 [95% CI: 0.93-0.97]) and asymmetry (ICC ranged from 0.39 [95% CI: 0.17-0.56] to 0.73 [95% CI: 0.32-0.81]) particularly at frequencies > or =4.3 Hz. Interrater reliability was good to excellent across all variables at frequencies < or =3.9 Hz.

Conclusions: Many patients had difficulty performing the VAT. The reliability estimates for phase and asymmetry, but not gain, were significantly affected by practice. Careful attention to patient preparation, instruction, and test monitoring including sufficient patient practice before data collection are likely to be critical factors to ensure quality data.