Evaluation of the Psychometric Properties of a Newly Developed Chinese Screening Tool for Speech Disorders in Patients With Parkinson’s Disease

Abstract

The study aimed to analyze the psychometric properties of a newly developed Chinese screening tool, the Chinese Version of the Speech Disorders in Parkinson’s Disease Questionnaire (SDPD-C). The SDPD-C contains a 24-item questionnaire with four assessment domains. Overall, 93 patients with idiopathic Parkinson’s disease (PD) (age 70.1 ± 8.9 years) and 76 healthy older adults (age 67.2 ± 8.1 years) participated in the psychometric analysis study. The internal consistency of the SDPD-C was .91 (four dimensions: .69–.85), and test-retest reliability was .91 (four dimensions: .85–.88). The SDPD-C was highly correlated with the Voice Handicap Index-10 and Movement Disorder Society-Unified Parkinson’s Disease Rating Scale II 2.1 (r = .83 and .78, respectively). The SDPD-C scores also differed significantly between stages 1 and 4 of the Hoehn and Yahr Scale (p < .05). The area under the receiver operating characteristic curve was .955 (95% confidence interval, .927–.983; asymptotic significance p < .001), and the optimal cut-off score of this study was 36, with a sensitivity of .849 and specificity of .947. The results indicate that SDPD-C showed good reliability, validity, accuracy, and discrimination. It can be used as a screening tool for speech disorders in patients with PD.

Keywords

speech disorders parkinson’s disease screening psychometric analysis dysarthria

Introduction

Hypokinetic dysarthria, a speech disorder, is characteristic among patients with Parkinson’s disease (PD). The symptoms of hypokinetic dysarthria include unintelligible and/or unnatural speech involving disorders related to phonation, respiration, resonance, articulation, and prosody (Duffy, 2013). These symptoms gradually affect communication in patients with PD, which is a progressive neurological disease (Skodda et al., 2013). An Australian study showed that most patients with PD had concurrent speech disorder, and only 59% of them received speech and language services (Swales et al., 2021).

Problems in language communication can affect the quality of life of patients with PD (Chu & Tan, 2019). Identifying patients’ perceptions of their speech intelligibility and life satisfaction could help clinicians better understand their patients’ needs when providing speech therapy services (Chu & Tan, 2019). Thus, early diagnosis and treatment are essential for patients with PD to maintain their communication skills and quality of life.

Perceptual speech and tool-based assessments are used to evaluate speech disorders in patients with PD. Speech therapists conduct speech assessments to determine the degree of speech impairment based on neurolinguistic testing and their clinical expertise. Prompt actions are advantageous for perceptual speech assessment. However, the reliability and validity of the evaluation can be affected by the subjective judgement of the evaluators.

Tool-based acoustic speech analysis is a relatively objective evaluation method compared with perceptual speech assessment. It can help identify significant laryngeal abnormalities, such as abnormal movement of vocal folds, vocal fold atrophy, or asymmetry (Yücetürk et al., 2002).

Linguistic communication is a real-life behaviour. If the language problems of patients with PD can be measured using a scale that reflects their language deficits and related feelings, individually tailored treatments could be provided. Therefore, self-assessment of speech disorders is clinically significant. At present, commonly used self-assessment tools for speech disorders in patients with PD include the Voice Handicap Index-10 (VHI-10) (Jacobson et al., 1997) and the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) (Goetz et al., 2008). The VHI-10 is a self-assessment scale for assessing functional voice disorders. It is not designed to address the characteristics of voice impairment in patients with PD. As speech impairment in patients with PD is multifaceted, the assessment of speech communication in these patients should consider the unique features of the speech mechanism, including respiratory muscles and muscle control.

The MDS-UPDRS is a comprehensive tool for evaluating disability in patients with PD, where only questions 2.1 “Speech” and 2.2 “Saliva and Drooling” (non-speech-related oral movements) are used for the self-evaluation of speech disorders. Therefore, MDS-UPDRS cannot cover all speech disorder problems in patients with PD.

Recently, a newly developed Chinese screening tool, the Chinese Version of the Speech Disorders in Parkinson’s Disease Questionnaire (SDPD-C), has been developed (Chen et al., 2019). It aims to identify markers of speech disorders in patients with PD. The SDPD-C is a textual description of the speech impairment status of patients with PD. Patients with PD can read the SDPD-C and rate their performance according to their speech impairment. A family member or health care provider can assist patients who cannot read because of their educational level and with completing the form. The content validity of the SDPD-C has been determined through experts’ validity reviews (Chen et al., 2019). This study aimed to analyse the reliability, validity, diagnostic accuracy, sensitivity, and specificity of the SDPD-C.

Methods

Participants

This study included 102 patients with PD who were initially referred by a physician from the Department of Neurology of a medical centre in southern Taiwan and then received a confirmed diagnosis of primary PD. Exclusion criteria included patients with cognitive impairment, as this could make it difficult for them to complete the questionnaire. Moreover, hearing impairment could induce speech and communication disorders. Therefore, patients with hearing impairment were also excluded from this study. Hearing impairment was identified as a failure to respond to 512 Hz and 1024 Hz tuning fork tests. Cognitive deficit was determined by a Clinical Dementia Rating (CDR) (Morris, 1993) score of <1. Ninety-three patients with PD participated in this study. This study also recruited healthy older adults aged >55 years from community centres to participate in the study. Their cognitive deficits and hearing impairment were evaluated using the Mini-Mental State Examination (MMSE) (Folstein et al., 1975) and the tuning fork test, respectively. Seventy-six participants were included in the healthy older adult group for analysis.

All study participants provided informed consent, and the study design was approved by the appropriate ethics review board.

Measurement tools

SDPD-C

The SDPD-C, a newly developed self-assessment scale, is a 24-item questionnaire with four assessment domains to screen for speech disorders in patients with PD (Chen et al., 2019). The four domains of the SDPD-C were defined based on the results of a literature review (Cohen, 1988; Duffy, 2013; Canter, 1963; Nakano et al., 1973; Dashtipour et al., 2018). The four domains are (1) articulation and speech-related oral motor function, referring to dysarthria and oral motor problems caused by difficulties in the movements of articulation in patients with PD; (2) phonation and resonation, referring to poor control of the respiratory muscles, resulting in sound problems caused by poor volume, tone quality, and resonance control during speech; (3) prosody and rhythm, referring to problems in tone and fluency caused by respiratory and vocal muscle weakness; and (4) emotional and nonverbal communication behaviour, referring to problems with interpersonal interactions caused by a reduction in nonverbal communication behaviours, such as facial expressions, gesture movements, and communication motives. A 5-point Likert scale was employed in the questionnaire. Scores ranging from 24 to 120 could be obtained, and a higher score indicated more severe speech disorders. The contents of the SDPD-C are shown in Supplemental Appendix 1.

MDS-UPDRS (Chinese Version)

The MDS-UPDRS was designed to assess the severity and progression of PD. The MDS-UPDRS was modified into four parts: (1) nonmotor aspects of experiences of daily living (six items assessed in an interview and seven items through self-assessment); (2) motor aspects of experiences of daily living (13 self-assessment items); (3) motor examination (18 items resulting in 33 scores based on location and lateralisation); and (4) motor complications (three items for dyskinesia and three items for fluctuation). This study assessed only items 2.1 and 2.2 related to speech, saliva, and drooling. The internal consistency for the second part of the MDS-UPDRS was α = .90 (Goetz et al., 2007).

VHI-10 (Chinese Version)

The VHI-10 comprises three subscales (functional, physical, and emotional) with 10 questions scored on a 5-point Likert scale, which are used to measure the self-perceived voice-related quality of life. The items are self-scored by patients according to their judgement of the extent to which voice impairment affects their daily activity functions, with higher scores reflecting more severe disorders. The internal consistency of the Chinese Version of the VHI-10 has been verified using 176 patients with voice disorders (α = .861) (Wang et al., 2011).

Procedure

Participants in the PD group underwent a physical examination by a neurologist, and motor symptom grading was based on the Hoehn and Yahr Scale (H & Y Scale) (Hoehn & Yahr, 1967), and a CDR test to confirm their eligibility for the study. The participants then underwent the tuning fork test to rule out hearing impairment. Finally, all the participants self-completed the SDPD-C, VHI-10, and MDS-UPDRS-II 2.1 and 2.2 questions. All the tests were completed within 2 h of taking antiparkinsonian medication. The healthy older adult participants also underwent the tuning fork and further MMSE tests to rule out hearing impairment and cognitive deficits and then also self-completed the SDPD-C.

Statistical analysis

Statistical analyses were performed using SPSS version 20. Statistical significance was set at p < .05. Reliability was evaluated in terms of internal consistency and test-retest reliability. Validity was evaluated in terms of criterion-related validity and discriminant validity. The sensitivity, specificity, and best cut-off score of the SDPD-C were calculated and determined using the area under the receiver operating characteristic curve (AUC) (Hanley & McNeil, 1982).

Internal consistency was measured using Cronbach’s α coefficient. Complete consistency was represented by α = 1, good consistency by α > .80, and poor consistency by α < .40 (Henson, 2001). The intraclass correlation coefficient (ICC) was used as an indicator of test-retest reliability. During the evaluation, 40 patients with PD were willing to undergo retesting, among whom 3 dropped out. Therefore, 37 participants with PD were selected to assess the test-retest reliability. The second test was performed 7–21 days after the first test, and the average interval between the first and second assessments was 11.7 days. In the interpretation of ICC values, values of <.40 indicated poor reliability, .40–.75 indicated good reliability, and >.75 indicated excellent reliability (Shoukri, 1999).

The Pearson correlation coefficients among the total scores of the SDPD-C, VHI-10, and MDS-UPDRS 2.1 and 2.2 were calculated to measure the criterion-related validity of the SDPD-C. The analysis was performed by testing the significance of the Pearson correlation coefficient (r). The strength of the correlation was defined by the r value distribution as follows: r = 0–.25, very low correlation; r = .26–.49, low correlation; r = .50–.69, moderate correlation; r = .70–.89, high or strong correlation; and r = .90–1.0, very high or strong correlation (Munro, 2005). Analysis of variance (ANOVA) was used to determine whether the SDPD-C scores differed significantly across the Hoehn & Yahr stages, which were used as indicators for evaluating the discriminant validity of the SDPD-C. Independent samples t-tests were performed to compare the mean SDPD-C scores among the groups.

Results

Participants’ characteristics

Overall, 93 participants aged 41–88 years were included in the PD group, comprising 46 males (mean age, 70.13 years [SD = 9.27]) and 47 females (mean age, 70 years [SD = 8.59]). The healthy older adult group included 76 participants aged 55–92 years, comprising 35 males (mean age, 68.09 years [SD = 8.73]) and 41 females (mean age, 67.22 years [SD = 8.10]).

Internal consistency of contents in the SDPD-C

The overall Cronbach’s α coefficient of the SDPD-C was .91, and that of the four domains was .81, .85, .69, and .69, respectively. These results showed that the SDPD-C had good internal consistency overall and in the domains of articulation and speech-related oral motor function and phonation and resonation.

Test-retest reliability

The overall ICC of the SDPD-C was .91. The test-retest reliability scores of the four domains were .88, .88, .86, and .85, respectively. These results indicated that SDPD-C had excellent reliability overall and in each domain.

Criterion-related validity

The VHI-10 and the questions about “speech” on the MDS-UPDRS 2.1 were moderately correlated with the SDPD-C (r = .83 and .78, respectively).

Discriminant validity

ANOVA was performed to determine whether there was a significant difference in the SDPD-C scores among patients with PD based on the H & Y stage classification. The results showed that participants in the four different stages exhibited significantly different scores on the overall scale as well as in each domain, as shown in Table 1. The Scheffe post hoc test conducted after ANOVA revealed a significant difference in the SDPD-C scores between patients with PD with H & Y stages 1 and 2 and those with H & Y stages 3 and 4.

Table 1.

Discriminant Validity Analysis of SDPD-C (n = 93).

	Hohen and Yahr Scale
SDPD-C	Stage 1 (n = 20)	Stage 2 (n = 33)	Stage 3 (n = 24)	Stage 4 (n = 16)
	M (±SD)				F	Post hoc test (Scheffe) stages
Total scale	44.85 (±15.36)	46.18 (±13.43)	57.46 (±16.89)	69.69 (±19.13)	6.46**	4 > 1,2
Articulation and speech oral motor function	11.60 (±5.54)	11.06 (±3.84)	15.63 (±5.14)	20.25 (±6.26)	7.70**	4 > 1, 2
Phonation and resonation	15.55 (±5.14)	18.45 (±6.70)	21.17 (±8.28)	24.19 (±9.19)	3.11*	4 > 1
Prosody and rhythm	6.60 (±3.60)	6.85 (±2.12)	7.83 (±3.63)	10.19 (±3.87)	4.13*	4 > 1, 2
Emotional and nonverbal communication behaviour	11.10 (±4.38)	9.82 (±4.13)	12.83 (±3.51)	15.06 (±3.28)	7.82**	4 > 2; 3 > 2

Note. *p < .05, **p < .01. SDPD-C; the Chinese Version of the Speech Disorders in Parkinson’s Disease Questionnaire.

Between-group differences

Table 2 shows the SDPD-C scores in the PD and healthy older adult groups. The mean total SDPD-C score and the mean scores in the four domains were 52.85 and 13.94, 19.52, 7.62, and 11.77, respectively, in the PD group and 27.84 and 7.70, 9.75, 4.30, and 6.09, respectively, in the healthy older adult group. There was no overlap in the 95% confidence intervals (CIs) of the four domains’ mean scores and the mean total SDPD-C scores between the PD and healthy older adult groups. The 95% CIs of the mean total SDPD-C score in the PD and healthy older adult groups are shown in Table 2. The mean score in the independent samples t-test was significantly different (p < .001, two-tailed) and showed significant differences in the four domains and total SDPD-C scores between the PD and healthy older adult groups.

Table 2.

The Scores of the SDPD-C in PD and Healthy Older Adult Groups (n = 169).

SDPD-C	PD group(n = 93)		Healthy Older Adult Group (n = 76)		PD- Healthy Older Adult
	Mean (SD)	95% CI	Mean (SD)	95% CI
Articulation and speech oral motor function	13.94 (6.023)	[12.70, 15.18]	7.70 (1.46)	[7.36, 8.03]	6.24***
Phonation and resonation	19.52 (7.766)	[17.92, 21.12]	9.75 (2.81)	[9.11, 10.39]	9.77***
Prosody and rhythm	7.62 (3.404)	[6.92, 8.32]	4.30 (.86)	[4.11, 4.50]	3.32***
Emotional and nonverbal communication behaviour	11.77 (4.286)	[10.89, 12.66]	6.09 (1.53)	[5.74, 6.44]	5.68***
Total	52.85 (18.085)	[49.12, 56.57]	27.84 (5.16)	[26.66, 29.02]	25.01***

Note. ***p < .001. SDPD-C; the Chinese Version of the Speech Disorders in Parkinson’s Disease Questionnaire.

Diagnostic accuracy

The diagnostic accuracy was evaluated based on the AUC (Hanley & McNeil, 1982). Figure 1 shows that the AUC of the SDPD-C was .955 (95% CI, .927–.983; asymptotic significance, p < .001). This indicated that the likelihood that a randomly selected individual who was a patient with PD had a higher SDPD-C test score than that of a randomly selected individual who was a healthy older adult person was 96% [95% CI, 93%–98%]. The AUC in this study indicated a high diagnostic accuracy (Petrie & Sabin, 2005).

Figure 1.

Receiver operating characteristic curve of the Chinese Version of the Speech Disorders in Parkinson’s Disease Questionnaire. Area under the curve = .955; 95% confidence interval, .927-.983; p < .001; cut-off score 35.5.

Sensitivity and specificity

The highest Youden-Index (sensitivity + specificity −1) (Youden, 1950) was used to determine the cut-off score. The optimal cut-off score was 35.5, with a sensitivity of .849 and specificity of .947. Patients with a score above the cut-off value were suspected to have speech disorders. The ratio of participants with a score of <35.5 in the PD group was 15% (95% in the healthy older adult group) while the ratio of participants with a score of >35.5 in the PD group was 85% (5% in the healthy older adult group), indicating that 36 was a suitable cut-off value.

The H & Y Scale is clinically used to describe the degree of impairment and comprises five levels, with higher levels indicating more severe impairment. Those with H &Y stages 1 and 2 had a mean total score of 45.68 (95% CI, 41.81–49.55), and those with H & Y stages 3 and 4 had a mean total score of 62.35 (95% CI, 56.40–68.30). Therefore, a score of >56 suggested the presence of severe speech impairment.

Discussion

The results of this study showed that the SDPD-C had excellent test-retest reliability, moderate validity, high diagnostic accuracy, and discrimination. Skodda et al. (2011) performed an acoustic analysis and reported that the vowel space area was smaller in the PD group, limiting tongue movement and affecting articulatory clarity. Our findings also demonstrated that patients with PD experienced difficulty in articulation and speech-related oral motor function.

Following an endoscopic examination, Bauer et al. (2011) found that patients with PD had irregular vocal fold vibration and incomplete vocal fold closure during vocalisation. Our findings also revealed that patients with PD experienced difficulty in phonation and resonation. Kent and Rosenbek (1982) found that four tones of speech in Chinese were flat and lacked pitch contrast in patients with PD. Our findings indicated that patients with PD experienced difficulty in prosody and rhythm.

McNamara and Durso (2003) found that as the duration and severity of PD increased, the severity of nonverbal communication problems, such as facial expressions, eye contact, and gestures during communication, intensified. Therefore, nonverbal communication is a crucial indicator for the clinical assessment of patients with PD in terms of interpersonal interaction and communication effectiveness. Our findings also suggested that patients with PD experienced difficulty in emotional and nonverbal communication behaviour.

The voice disorder of patients with PD has unique characteristics. Although the VHI-10 is a common voice disorder assessment tool in clinical practice, it does not cover all voice disorders in patients with PD. Respiratory muscle dysfunction in patients with PD affects tone and resonance maintenance as well as voice functions (Schulz & Grant, 2000). The phonation and resonation domain in the SDPD-C assesses voice and speech problems caused by respiratory muscle dysfunction in patients with PD. Moreover, dysarthria affects imprecise articulation in patients with PD (Yang et al., 2020). Item 2.1 (speech impairment assessment) in the MDS-UPDRS describes the symptoms but does not examine the speech impairments individually caused by articulation and oral motor function. However, these impairments can be assessed using the articulation and speech-related oral motor function domain in the SDPD-C. Furthermore, item 2.2 on the MDS-UPDRS assesses only saliva and drooling. Nonverbal communication dysfunctions in patients with PD also include reduced facial expression (mask face) due to slow movement, muscle stiffness, and absence of blinking and smiling (Benke et al., 1998). These aspects of nonverbal communication dysfunction can be assessed using the emotional and nonverbal communication behaviour domain in the SDPD-C.

In summary, the SDPD-C can be used to evaluate speech and language impairment more comprehensively than the current speech impairment self-assessment scales for patients with PD, such as the VHI-10 and MDS-UPDRS, which have certain limitations.

The AUC reflected the scale’s accuracy in differentiating the presence or absence of the disease and can serve as a reference indicator for disease diagnosis. The AUC in this study was .955 (95% CI, .927–.983; asymptotic significance, p < .001), indicating that the SDPD-C had high diagnostic accuracy. The diagnostic accuracy could also be assessed using the ROC curve, which combines the two indicators, sensitivity and specificity, for empirical studies (Hanley & McNeil, 1982). The sensitivity indicates the rate at which those with the disease are determined to be positive. Conversely, specificity indicates the rate at which those without the disease are determined to be negative. The consistency of these two indicators can be used as a diagnostic tool, with higher values indicating better stability in assessments performed using the scale (Green & Swets, 1966).

In this study, Youden-Index was used to establish the cut-off scores to identify patients with PD with speech problems. The optimal cut-off score for the SDPD-C was 35.5, with a sensitivity of .849 and a specificity of .947, indicating that the SDPD-C was highly stable, and a score of >36 indicated a risk of speech impairment. Collectively, this indicates that the SDPD-C has high diagnostic accuracy as well as sensitivity and specificity.

Speech impairment in patients with PD may manifest in the early stages and worsen as the disease progresses (Miller et al., 2006). According to a report by Miller et al. (2011), referrals are generally considered later than expected in PD speech disease progression. Studies and interpretation of data from studies in early PD are limited, and best practices of speech therapy have not been established (Ciucci et al., 2013). The presence of self-perceived mild speech impairment in the initial years of post-diagnosis in patients with PD may support the need for intervention to improve or sustain function over time (Watts & Zhang, 2022).

The types of treatment for speech disorders in patients with PD include medical, surgical, and behavioural types. Speech treatment is reportedly helpful for patients with PD, including training for exercises to help them breathe and tips on speaking slowly and clearly (Yorkston et al., 2017). Clinical speech therapy is the basis of treatment for speech and voice characteristics in patients with PD, such as evidence-based practice for behavioural speech and Lee Silverman Voice Treatment to improve vocal loudness and pitch range (Ramig et al., 2018).

The results of this study indicate that the SDPD-C is a good screening tool for the diagnosis of speech disorders in patients with PD. PD is a chronic degenerative disease of the central nervous system, with most patients showing slow disease progression. According to Dias et al. (2016), speech disorders are not related to the patient’s age at onset but are positively correlated with the disease course. Therefore, there is a need for a reliable, valid, and accurate screening scale to rapidly diagnose speech disorders in patients with PD for timely referral to treatment. The SDPD-C is a scale that meets these criteria.

The study limitations involved those associated with sampling, as geographic proximity was considered and participants were recruited from only southern Taiwan. Hence, further studies on different language versions of the SDPD-C conducted in different regions and patient populations are warranted.

Conclusions

The SDPD-C showed excellent test-retest reliability, moderate criterion-related validity, and high diagnostic accuracy, sensitivity, and specificity in patients with PD in Taiwan. It could also be used as a screening marker for managing the severity of speech disorders in patients with PD to rapidly assess speech disorder problems, thereby providing a basis for referral and appropriate medical care.

Supplemental Material

Supplemental Material - Evaluation of the Psychometric Properties of a Newly Developed Chinese Screening Tool for Speech Disorders in Patients With Parkinson’s Disease

Supplemental Material for Evaluation of the Psychometric Properties of a Newly Developed Chinese Screening Tool for Speech Disorders in Patients With Parkinson’s Disease by Chi-Lin Chen, Ching-Huang Lin, Chen-San Su, Hsiang-Chun Cheng, Li-Mei Chen, Rong-Ju Cherng in Evaluation & the Health Professions

Footnotes

Acknowledgments

We would like to thank all the participants. We would also like to thank Editage () for English language editing.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical Approval

This study has been approved by the IRB. IRB No: VGHKS17-CT11-07

ORCID iDs

Chi-Lin Chen

Rong-Ju Cherng

Supplemental Material

Supplemental material for this article is available online.

Author Biographies

Dr. Rong-Ju Cherng is a Professor of the Institute of Allied Health Sciences and the Department of Physical Therapy at National Cheng Kung University, Taiwan. Dr. Cherng received her B.S. degree in Physical Therapy from National Taiwan University, Taiwan, then M.A. degree in Physical Therapy from New York University, NY, USA and Ph.D. in Biomedical Engineering, National Cheng Kung University, Taiwan. Her research interests include motor skills disorders, motor development and rehabilitation. Dr. Cherng has been serving as a reviewer for many journals, such as Archives of Physical Medicine and Rehabilitation, Disability and Rehabilitation, Research in Developmental Disabilities, Gait & Posture, etc.

Ms. Chi-lin Chen is a lecturer in the Department of Speech and Language Therapy, Chung Hwa Medical Technology University, Taiwan. Ms. Chen is a clinical Speech and Language therapist. Her research interest is in the treatment and rehabilitation of motor speech disorders.

Dr. Lin is a neurologist in the Section of Neurology, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan. He is an expert in cerebrovascular diseases.

Dr. Su is a neurologist in the Department of Neurology, Park One International Hospital, Kaohsiung, Taiwan. She is an expert in movement disorders.

Dr. Cheng is an Assistant Professor in the Department of Speech Language Pathology and Audiology at Hungkuang University. She has training in both physical therapy and speech therapy, her Ph.D. from the Institute of Allied Health Sciences at the National Cheng Kung University of Tainan. During her former career in hospital based pediatric speech therapy and physical therapy, she taught integrated therapy to pediatric speech therapy and physical therapy. Her research interest included integrating evidence-based practices from perceptual training into physical therapy to address applied behavior analysis, and to treat children with developmental disabilities.

Li-Mei Chen, Ph.D. is Professor at National Cheng Kung University (Taiwan). Her major research focuses on early speech development in Mandarin Chinese in both typically developing children and children with speech and language disorders.

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