Psychometric Characteristics of Different Versions of Vocal Tract Discomfort (VTD) Scale: A Systematic Review.

BACKGROUND: This review compare different Vocal Tract Discomfort (VTD) versions. This comparison is based on their validity and reliability parameters in the translation and adaptation process. We aimed to prepare numerical evidence to prove the validity of this easy screening tool. VTD is able to perform an accurate diagnosis of voice discomforts, particularly in primary stages.
METHODS: Articles were selected from databases including Google Scholar, PubMed, Science Direct and Scopus. Our relevant papers were gathered by searching the phrase: VTD in titles, abstracts, and keys. Studies not followed an adaptive procedure were excluded. Based on the selection criteria, out of 23 collected articles, eight were studied in this review.
RESULTS: Standard psychometric protocol steps were followed in all selected articles and simultaneously high reliability and validity were reported in their translation procedure. Such analogous results may confirm the efficacy of this research tool.
CONCLUSION: This review affirms VTD, perceptual patient-based scale, as a valuable evaluation tool to investigate the occurrence of voice disorders. Based on its structure and performance, VTD can work as a quick and precise source for predicting vocal discomforts. Moreover, this capability can help professional therapists to plan more efficient treatment procedures. The other important advantage of VTD is its diagnostic and prognostic capacity to inform patients about their current and future conditions so that they would be motivated to follow treatment procedures more consistently.

Introduction

According to WHO declaration, there is not adequate information to assess before-after therapy outcomes and to demonstrate the grade of diseases (1, 2). Since 1990s, the world has widely taken questionnaires as standard tools to investigate the effects of different issues on an individual’s health (3–5). Moreover, questionnaire is considered as a common facilitative method to provide quick and informative data as a supplement to other data collection tools (3, 5–8). Questionnaires have also been applied to clarify main patient-related discomfort and consequently to direct treatment choices (3, 5, 9). In addition, self-evaluation questionnaires potentially lead to more successful multidimensional voice assessment around the world (2, 3, 5, 6). Regularly, questionnaires are adapted by expert translators to determine the exact need for clinical management and to make them appropriate research tools in other languages (5, 10).

Although numerous studies demonstrated that objective measurements are essential in voice problem diagnosis, they are not proved useful to measure the patient’s self-perception of his disorder’s degree (3, 5). Despite the existence of many objective assessments for speech manners in children and adults, the main role of patient-centered measurements to reveal the details of their disorders has not been proven (3, 5, 11). To demonstrate the importance of these instruments in identifying factors causing voice disorders, researches have recently applied self-assessment questionnaires to quantify the impact of a voice disorder on the subject’s self-evaluation (2, 3, 5, 9). Nevertheless, there are few questionnaires, which do this in the current condition (5). A well-structured tool for self-assessment of MTD in different voice disorders is the vocal tract discomfort (VTD) scale (12). However, some documents have proven the VTD application is not limited to MTD and can support other voice disorders (10). In other words, these self-evaluation scales provide the therapist a comprehensive view to manage the intervention program more efficiently (2–5).

Numerous middle-aged people (10%–40% of voice disorders) suffering from muscle tension dysphonia (MTD), extensively use their voice in stressful situations (10, 13–15). Furthermore, this pathological situation can motivate physical vocal tract discomfort (13, 15, 16). All of these changes influence mental health and disrupt individual’s functions in the social and occupational field (6, 8, 11, 14, 16). MTD is defined as excessive tension in the vocal and laryngeal muscles (8, 13, 14, 16). MTD has primary symptoms such as tickling, irritation, dry mouth, and throat obstruction feeling (called “lump”) (4, 8, 13). There are not enough clinical guidelines to provide a standard voice assessment protocol (2, 17, 18). Therefore, establishing clinically practical guidelines, which guarantee the responsiveness of treatments, is strongly recommended (4, 5, 17). This suggestion is based on the need to develop a conceptual framework to produce uniform evidence by a comprehensive set of methods (2, 5, 17). Such insufficiency of evidence to provide a clear diagnosis for voice disorders (such as MTD) leads us to apply more accurate evaluations such as self-assessments (2, 5, 6, 8, 9, 11, 15, 16, 18).

The VTD as a self-administered scale is capable of discriminating between healthy participants and patients with MTD (2, 16, 19). This reliable and valuable perceptual instrument measures the severity and frequency of difficulty that may be experienced in the vocal tract (19). This measurement addresses 8 qualitative descriptors included in the VTD questionnaire, namely burning, tickling, sore, dry, aching, irritable, tight, and lump in the throat (11). Each individual quantifies severity and frequency on a 7-point Likert-type scale, 0 to 6. Each frequency and severity subscale is related to a special state. In frequency, 0 means never, 1–3 means sometimes, 3–5 means often, and 6 means always. In severity, 0 means none while 1–3, 3–5 and 6 mean mild, moderate, and extreme, respectively. Each subscale’s total score ranges from 0 to 48 ((max score) 6× 8 (all items)) (10).

Furthermore, the declared correlation between the VTD scale and other conventional standardized assessment tools, such as the Voice Handicap Index (VHI) or max phonation time, conforms the clinical value of this self-assessment instrument (3, 5). Moreover, the VTD scale can be used as an optimal tool to monitor progression after voice therapy such as laryngeal manual therapy (3, 17, 19). These findings led to the development of voice self-assessment, which helps professionals to provide more precise assessments and effective treatments.

The importance of trans-cultural studies will be more obvious owing to the information gathered about the reliability, validity, and responsiveness of different language versions for VTD (3, 7). Currently, there are many versions of VTD translated and adapted into various languages including German, Arabic, Argentine, Polish, Flemish, Italian, Norsk, and Persian; yet only six studies have been purported to compare patient group with normal individuals (10, 20–25). Commonly validity and reliability are as psychometric factors used to evaluate the quality of questionnaires in research studies (5). Generally, researchers are providing a framework for examining these two concepts in qualitative research (17). Moreover, recent psychometric studies have raised responsiveness as another essential concept in the methodological study of scales (5, 7). Responsiveness indicates the scale’s capacity to determine changes in patient condition and reflect intervention efficacy and outcomes (5, 7, 19).

We come up with several reasons to review different versions of VTD. First, it is generally used in clinics for MTD patients (11, 12). Second is the high applicability of VTD as a scale to evaluate the frequency and severity of any discomfort in the vocal tract, which can end in better treatments (10, 26). Third is its adaptive procedure, which seems to be more important for future medical applications and is presently available in nine languages (10, 20, 23, 26).

Based on the high reliability and validity of VTD versions among several languages, the importance of conducting transcultural studies and the number of participants would be more highlighted (5). Thus, regarding the importance of VTD in the evaluation of voice disorders (especially MTD) and its prevalent application in other languages, this review was formed to provide a valid report to contribute to medical instrumental awareness (4). In other word, we intend to address the insufficiency of evidence for self-evaluation via comparing the reliability and validity of the VTD scale in various languages.

Thus, our research question enquired, “What are the reasons for this global tendency of experts in assessing voice disorders to use VTD? Moreover, is there any coherent statistical evidence in different versions of VTD that demonstrate the higher ability of this tool than the previous ones? We hoped to determine the supplementary position or replacement of VTD in the current world of evaluation and voice therapy in our clinics as an additional aim through answering these questions by reviewing VTD versions.

Methods

For the aim of this review, we collected relevant studies based on the eligibility criteria. These nine articles which are different versions of VTD were published between 1993 [date of original VTD that developed by Mathieson] and 2020.

Our inclusion criteria insisted that all papers needed to be original papers, written in English language on human studies, and contained translation, reliability, and validity reports. Qualitative and case report papers were excluded. Data Collection was carried out by electronic searching in multiple resources including; Web of Science, PubMed, Science Direct, and Scopus, Google Scholar, ProQuest (as gray literature). All these databases were searched by the phrase: “” (VTD) in titles, abstracts, and keywords (Table 1). We applied the only Title or Abstract limitation and did not run any filters. All 23 papers were checked for relevance to our research questions by titles and abstracts; next, 14 unrelated ones that did not follow cultural adaptation procedures were excluded. Because of non-English text, one article was also excluded. In Fig. 1, we illustrated the selection process of these 8 articles that we finally included in our review study based on PRISMA guidelines (27, 28).

Table 1:

Search strategy in different Databases

Databases	Search strategy
Scopus	TITLE-ABS-KEY(“vocal tract discomfort”)
Web of science	TI=”vocal tract discomfort “
Science direct	“vocal tract discomfort”(abs/title/key)
PubMed	“vocal tract discomfort”[Title/Abstract]
Scholar	In the title: “vocal tract discomfort “
ProQuest	TI(“vocal tract discomfort “)

Fig. 1:

Study selection chart for finding different versions of VTD (29)

Results

Based on the searches in the mentioned databases, and after filtering the output by title/abstract, mainly 8 articles were obtained. We omitted the North version of VTD because of its non-English text. Totally, 7 papers were confirmed to be reviewed. The results of these studies written in English but originally belonged to other languages are summarized in Tables 2–4. Some details are presented as follows.

Table 2:

Validity and Reliability parameters in translated versions of VTD across languages. Severity subscale

Language	Content validity	Face validity	Construct validity	Internal consistency (Cronbach’s alpha coefficient)	Test-retest reliability	Cut off point	Roc curve (R2)
Korean	-	-	-	+	+	-	-
Argentine	-	-	-	0.7–0.9	-	-	-
Arabic	-	-	Done	0.874	-	23	0.804
Italian	-	-	Done	0.94	ICC:0.91–0.97	-	-
German	Done	Done	0.674	0.919	-	25.75	-
Persian	Done	-	P<0.001	0.672-0.732	ICC: 0.91	-	-
Flemish	-	-	P<0.001	0.05	-	-	-
Polish	-	-	P<0.000	0.936	-	-	0.932

Table 4:

Evaluation of different psychometric features among VTD versions in different languages

Languages	Publish date	Patient number	Control group	Panel	Translates by voice expert	Back translation	Cultural equation	Validity	Reliability	Correlation with VHI (total score)
Korean	2020	159	+	−	+	−	+	+	+	+
Argentine	2018	107	+	−	−	−	−	+	+	−
Arabic	2017	97	+	−	−	−	−	+	+	+
Italian	2017	102	+	+	+	+	−	+	+	+
German	2016	107	+	+	+	+	+	+	+	+
Persian	2015	100	+	+	+	+	+	+	+	+
Flemish	2015	333	−	−	−	−	−	+	+	+
Polish	2012	218	+	−	−	−	−	+	+	+

Discussion

The purpose of this review was to scrutinize the differences among versions of the VTD scale as a recent easy-to-use diagnostic tool in various clinical settings (2, 3, 19). Although VHI was the most common tool in these communities, there was a great need to get access to a self-assessment tool that would give symptom-based insights and information to clinicians (3–5, 24). On the other hand, validity and reliability of scale are developed in the natural context and standard language of each culture. Hence, the current psychometric procedure tries to represent the national value of languages (2, 10).

The main source of our review study was different versions of VTD adapted to several linguistic and cultural contexts (12). Based on our revision, in all VTD versions which had the expert committee members and the professional translators in their research studies accepted the level of new cross-cultural translated VTD equivalence (conceptual, experimental, and idiomatic) (5, 26). Maybe the single-word structure of items in the English VTD scale was the reason for this acceptance (except “Lump in the throat”) (21, 26). The main validity and reliability parameters that considered in this review study are internal consistency, test-retest reliability, clinical validity, and responsiveness that were high in all VTD versions (5, 19).

We observed several differences among the VTD adapted versions specifically over their target groups. For example, the Italian version targeted dysphonic patients with various etiologies (neurologic, organic, and functional) (26). In German and Flemish studies, both organic and functional clients with dysphonia were recruited 10. Persian study focused merely on MTD patients (24). Whereas the Polish version concentrated on occupational dysphonia (22). The VTD was applied by unskilled persons; few articles have employed unprofessional translators in the voice field to simplify professional terminology (5). Besides, papers in Persian, Arabic, and Italian context used speech and language pathologists to translate VTD (only for forward translation) (20, 24, 26). The other considerable point in a few VTD versions such as Persian and German was its separate and independent administration by different translators (10, 24). This method promotes translation reliability (1). On the other hand, it can reduce the prejudice that may arise due to the translators’ opinions. Moreover, this technique can prevent the translators’ viewpoints to be affected by each other (1, 5).

Due to the complication of voice disorders, accurate diagnoses and comprehensive treatment are required via multiple approaches (2, 3, 6–8, 11, 16, 17). Hence, we need to confront the voice problems by multidisciplinary strategies through breadth services (8, 17). Both the VHI and VTD can add a subjective aspect to the multidimensional voice evaluation for various clinical decision-making procedures (5, 9, 10, 20–22, 24, 26). All VTD versions reported high values of correlation between its frequency and severity subscale and VHI total scores (3). Both tests are reliable instruments (5, 22). Their acceptable correlation allows them to be applied independently or in collaboration with clinicians as a part of their evaluation protocol and voice therapy prognosis (3, 9, 20, 29, 30). Consequently, the high P-value gained from the correlation between these two tools, VHI-30 and VTD, affirms the strong reliability of VTD in precise distinction and clinical self-rating (18, 20, 22, 26). However, some studies like Flemish reported a weak correlation (21). This can be attributed to considering various aspects of a vocal disorder with different question types by these two scales (5, 9, 10, 20, 21, 24, 26). The VHI indirectly evaluates symptoms, assesses the self-perception of vocal problems that could be formed as a vocal handicap’s perspective (1, 3–5, 10, 20, 24, 26). Whereas the VTD directly evaluates the degree of vocal tract discomfort sense (by its severity and frequency subscale) (10, 20, 24, 26). Moreover, VTD can be more precise in discovering additional vocal load by measuring physical sensations (19, 20). This ability is the result of VTD’s clear formulation, which addresses symptoms present in disease-related states, especially in a patient with a severe vocal load (4, 9, 13, 14, 26). Moreover, VTD can be used as an easy self-assessment tool to predict the vocal handicap’s outcome in 5 min or less (26). Furthermore, this potency to provide a quick independent and supplementary information in the head and neck region made VTD to be highly recommended as an introduction of the daily clinical session and as a part of standard voice evaluation protocols (2, 5, 8, 17, 19, 26). Symptom evaluation, commonly considered as the main goal of consultation, is a confident way to meet the patient’s needs (3, 21, 23). In addition, this assessment style enables us to apply an appropriate treatment for each patient based on their discomforts (3, 4, 10, 17). In addition to the robust role of VTD in the evaluation of musculoskeletal and chronic inflammation vocal discomfort, it is proven that VTD can monitor the efficacy of various interventions like voice therapy, surgery, etc. (1, 3, 6, 19, 22, 23, 26).

Seven studies reviewed report similar restrictions. All the articles emphasize that their study should be carried out in larger sample sizes, which may affect the obtained results (3, 5–7). In fact, each article enrolled more participants than the original VTD version developed by only 36 participants (12). Based upon the fact that the original population is in a mixture of various dysphonia (3), it is strongly suggested to apply VTD in different classified-types of voice disorders (20–22). VTD is applicable in determining the effectiveness of treatments (4, 7, 10, 24, 26). Thus, it is highly recommended to perform VTD in longitudinal studies before and after specific treatment to record the results by including subjects’ symptomatic specifications like length and degree of voice disorders (2–4, 6, 20, 22, 24, 26). Accordingly, VTD can present specific cut-off points for each type of therapy (6). However, in the VTD adaptation procedure, the appropriate classification among various patient groups has not yet been established (19, 20, 26). Moreover, future research studies should clearly differentiate between patient groups and healthy groups by the VTD cutoff point (5). Consequently, defined cutoff points make them to be employed as the best screening tools for large populations (3, 18).

This review validates that the VTD scale is a reliable and valuable perceptual indicator for sensory changes in the vocal tract tissues among voice disorders (7, 10, 19, 20, 22–24, 26). The VTD can clinically provide beneficial data that is not obtained by other patient-based scales (3, 10, 19–24, 26). Thus, in a time-limited situation, the VTD can work as a quick and low-cost source for predicting vocal discomfort according to the individual’s perception of handicap (3–5, 8). VTD’s immediate and accurate diagnosis gives a chance to voice therapies to present a cost-effective and on-time treatment (2, 3, 8, 9, 17, 20, 26). On the other hand, VTD’s outcome informs the patient about his/her voice disorder (4, 8, 13, 26). Furthermore, VTD can bring a strong motivation for patients to follow treatment procedures more insistently (2, 8).

Conclusion

Application of VTD, in combination with other objective clinical evaluation methods, leads us to clarify the complicated nature of voice disorders more than ever. Actually, this combination provides a comprehensive and precise method for assessment. Further, VTD can indicate many complex aspects of throat symptoms that are related to voice disorders while other voice assessment scales cannot demonstrate them. VTD’s measurement reveals some symptoms that are not among the main purpose of voice therapy but have been affected significantly after interval treatment. Consequently, this diagnostic tool can be an evidence for speech and language pathologist to signify treatment responsiveness by VTD. Moreover, VTD can help clinicians to perform voice therapy based on frequency and severity of some specific symptoms of disordered voice that are indicated by the patient.

Ethical considerations

Ethical issues (Including plagiarism, informed consent, misconduct, data fabrication and/or falsification, double publication and/or submission, redundancy, etc.) have been completely observed by the authors.

Table 3:

Validity and Reliability parameters in translated versions of VTD across languages Frequency subscale

Language	Content validity	Face validity	Construct validity	Internal consistency (Cronbach’s alpha coefficient)	Test-retest reliability	Cut off point	Roc curve (R2)
Korean	-	-	-	+	+	-	-
Argentine	-	-	-	0.7–0.9	-	-	-
Arabic	-	-	Done	0.884	-	23	0.824
Italian	-	-	Done	0.92	ICC:0.92	-	-
German	Done	Done	0.674	0.919	-	25.75	-
Persian	Done	-	P<0.001	0.721–0.769	ICC: 0.93	-	-
Flemish	-	-	P<0.001	0.05	-	-	-
Polish	-	-	P<0.000	0.930	-	-	0.932