Variability of electroglottographic glottal closed quotients: necessity of standardization to obtain normative values.

Objective: To demonstrate the variability of electroglottographic measurements of the glottal closed quotient (GCQ) in normal subjects by the calculation method used, fundamental frequency, and intensity.
Design: Prospective study.
Setting: Tertiary university-based referral center.
Subjects: Twenty healthy male volunteers without laryngeal disorder. Three successive sustained productions of the vowel /a/ were performed by each subject. Electroglottographic recordings of GCQ were obtained using the criterion level method, which defines an approximate duration of glottal closure and opening. Glottal closed quotient values were calculated based on criterion levels ranging from 10% to 40%.
Main Outcome Measures: The extent of correlation between GCQ variation and the mean fundamental frequency and intensity.
Results: As the criterion level increased, a decrease in the mean GCQ was recorded, which was significant with a 10% criterion level increase, up to a critical level of 25%. A significant positive correlation was found between GCQ and the variables of fundamental frequency and intensity.
Conclusions: This study demonstrated significant effects of the criterion level used, fundamental frequency, and intensity in the determination of normative values of GCQ. Normative values can only be assessed through the standardization of one criterion level reached by consensus.