Item Hierarchy of Vocal Fatigue Index (VFI) in School Teachers-A Study from South India

The study aimed to identify the item hierarchy of the Vocal Fatigue Index (VFI) in school teachers using Mokken Scaling Analysis (MSA).

A total of 362 school teachers from five zones in Chennai city, southern part of India, participated in the study. All subjects completed a subject-information form that had details such as age, sex, duration of vocal demand per day, number of classes taken, grades taught, and years of experience and VFI. Based on the VFI factor-I scores, teachers were segregated into three groups, viz, No Fatigue (<11), Low Fatigue (11-24), and High Fatigue (>24). Percentage analysis, Mann-Whitney U, and Pearson's chi square was done for finding the association of variables (listed above) with vocal fatigue and MSA.

Two-hundred and seventy-five teachers (75.5%) identified themselves with vocal fatigue, and 87 (24%) others reported no vocal fatigue. The highest percentage of fatigue (63.18%) was documented in factor II, followed by factor III (48.90%) and factor I (40.38%). Mann-Whitney U test revealed a significant difference in vocal fatigue experience between males and females (P = 0.01). Pearson chi square showed a positive association between factor I and years of experience in teachers (P = 0.02). No significant correlation was observed between other variables and factors of VFI. MSA divided the VFI scale into two, scale 1 (factors I and II) and scale 2 (factor III). On segregation, several reliable scales were obtained, however, all the scales had a low Loevinger's coefficient.

VFI, though a reliable tool, did not capture the underlying trait of vocal fatigue completely in school teachers as a population. This study ascertains the need to develop a tool that is specific to occupation/profession, geographic, sociocultural, and ethnic group. Mere adaptations and translations of tools may not necessarily suffice for clinical utility and application.