Measurement Reliability of Phonation Quotient Derived From Three Aerodynamic Instruments.

OBJECTIVE: The purpose of this study was to examine parallel forms reliability between two hand-held spirometers and a pneumotachograph-based system for vital capacity and derived phonation quotient measurements.

STUDY DESIGN: This is a prospective, repeated measures design.

METHODS: A total of 20 adult males were tested using three aerodynamic instruments-Baseline windmill-type spirometer, Contec SP10 digital spirometer and the Pentax Medical Phonatory Aerodynamic System (PAS), Model 6600 for measures of vital capacity. Phonation quotient was calculated using vital capacity from each instrument along with maximum phonation time. Repeated measures analyses of covariance (ANCOVAs) were performed to test for main effects of the instruments on vital capacity and phonation quotient, with age as a covariate. Pearson Product Moment correlation was performed to assess measurement reliability between the instruments.

RESULTS: Statistically significant differences on ANCOVA were seen in vital capacity measures for the digital spirometer compared with the windmill spirometer and PAS. No differences were found between any of the instruments for phonation quotient. Large and positive correlations were present between all three instruments for both vital capacity and phonation quotient measurements.

CONCLUSIONS: Strong parallel forms reliability in measures of vital capacity and derived phonation quotient was seen among the three instrument systems, although measurement precision was different when comparing the digital spirometer to two other instrument types.