Adaption and psychometric evaluation of the Hindi version of Neck Disability Index in the rural population of Northern India: A cross cultural study

Background To ensure the validity and therapeutic utility of the Neck disability index (NDI) scale, translations, cultural adaptations and psychometric evidence is necessary. This study aimed to address the absence of a suitable and validated Hindi version of the NDI for the rural population. The specific objectives were to translate, adapt, and evaluate the psychometric properties of the newly developed Hindi version of the NDI. Methods Following guidelines provided by the American Association of Orthopedic Surgeons, the original English NDI scale was cross-culturally adapted into Hindi. The adaptation process included translations (forward and backward), expert committee review, pre-testing and cognitive debriefing with 30 individuals experiencing chronic non-specific neck pain. The outcome of this process was the creation of the Hindi version of the NDI, termed NDI-Hi. Subsequently, NDI-Hi was administered to 211 participants with neck pain from multiple centers for psychometric testing. The evaluation involved test-retest reliability over a 48-hour interval, factor analysis, assessment of internal reliability measures, and criterion-related validity by comparing it with the NPAD-Hindi version. Results The NDI-Hi version exhibited favorable psychometric properties, including good test-retest reliability with an intra-class correlation coefficient (ICC) of 0.87. Internal consistency of the scale was high, indicated by Cronbach’s alpha coefficient (α) of 0.96. The standard error of measurement (SEM) was determined to be 2.58, and the minimal detectable change (MDC) was calculated to be 7.15. Furthermore, the NDI-Hi showed significant correlation with the NPAD-Hindi version, with a correlation coefficient (rho) of 0.86, and a p-value of less than 0.001. Conclusions The NDI-Hi demonstrated validity and reliability as an outcome tool for assessing neck disability. It can be effectively utilized in clinical practice and research settings involving Hindi-speaking individuals with chronic non-specific neck pain. The adapted scale is particularly well-suited for the rural Northern Indian Hindi-speaking population.


Introduction
Non-specific neck pain is characterized by lack of pathognomonic signs and symptoms (Bernal-Utrera et al., 2020) and neck pain is the second biggest contributor to the global disability-adjusted life years among musculoskeletal disorders (Blyth et al., 2019).Around 50% of adults experience neck pain annually, leading to a poorer quality of life (Safiri et al., 2017).Disability related to neck pain represent a substantial socioeconomic burden (e.g., health care utilization, work absenteeism, and lost productivity) (Manchikanti et al., 2009).In 2016, among the 154 conditions, low back and neck pain had the highest health-care spending in the United States estimated at USD 134.5 billion (Dieleman et al., 2020).In rural India, the average expenditure on healthcare per family in Indian rupees is INR 3,040.82 per month (Patil et al., 2018), but musculoskeletal disorders are yet to be included in National Health Policy 2017 (Gupta & Kumari, 2017).Individuals with non-specific neck pain experience of physical (e.g., pain and disability) and psychological (e.g., anxiety, depression, and fear avoidance beliefs) concerns (Simula et al., 2019).Patient-reported outcome measures (PROMs) are commonly used in research and clinical settings to report physical and psychological problems in individuals with neck pain (Wirth et al., 2016;Lee et al., 2015).The NDI is a reliable, valid, and commonly used PROM to evaluate physical problems (pain and disability) among individuals with neck pain, which has been translated into many different languages like; Turkish (A.T. V. Study, 2008), Brazilian (Cook et al., 2006), Portuguese (Cook et al., 2006), German (Awaji, 2016), French, Swedish (though modified) (Lee et al., 2006), Korean (Song et al., 2010), Iranian (Mousavi et al., 2007), Dutch (Reneman, 2012), Greek (Trouli et al., 2008), Italian (Monticone et al., 2012), Arabic (Khair et al., 2020), Japanese (Nakamaru et al., 2012), Polish (Misterska et al., 2011), Thai, Punjabi (Sandal et al., 2021) and Marathi language (A.M. V. Study, 2015).The translation of a commonly used questionnaire facilitates cross-cultural and cross-linguistic comparisons and sharing of findings, as well as comparisons between other groups and clinical trials to ascertain the functional ability of the Indian population suffering from neck pain.Cross-culturally applicable questionnaires need to be linguistically translated to enhance comprehension and culturally appropriated to preserve the tool's content validity.According to the 2011 National Census of India, of the 1.3 billion Indians living worldwide, approximately 0.322 billion are native speakers of Hindi language.Language barriers are reported to have major impact on the quality of healthcare particularly when the healthcare providers and patients do not share a native language (Almutairi et al., 2020).Considering the factors like limited healthcare access in rural India, growing burden of musculoskeletal disorders including neck pain, possible language barriers, and the need for an accurate, relevant, and context-specific outcome measure to evaluate the disability among neck pain patients in India (Principles et al., n.d.;Sidiq et al., 2022).
In our extensive search, authors found one published work that aimed to translate, adapt and perform test-retest reliability, validity of the Hindi-version of NDI (Shakil et al., 2011), but the authors reported of not conducting the validity test due to feasibility constraints.We found that the authors of the previous version did not follow steps recommended or guidelines REVISED Amendments from Version 1 Here are the major differences between the two versions of the article: 1. Focus and Scope Clarification: The revised version explicitly emphasizes the need for a validated Hindi version of the Neck Disability Index (NDI) specifically for the rural population.It underscores the importance of cultural adaptation and psychometric validation to ensure the tool's relevance and reliability in this context.

Methodological Details:
The revised version provides more detailed methodological steps, adhering closely to guidelines from the American Association of Orthopedic Surgeons for cross-cultural adaptation.It outlines the stages of translation, expert review, pre-testing, and cognitive debriefing in greater detail, thereby enhancing transparency and replicability.
3. Participant Details: While both versions mention participant numbers and the general condition (chronic non-specific neck pain), the updated article specifies the demographic focus on rural Hindi-speaking individuals.It highlights the sample size used for both adaptation (30 individuals) and psychometric testing (211 participants from multiple centers), offering a clearer picture of the study's population.

Psychometric Results:
The revised version provides updated psychometric results, including specific values such as the intra-class correlation coefficient (ICC) of 0.87 for test-retest reliability, Cronbach's alpha coefficient (α) of 0.96 for internal consistency, standard error of measurement (SEM), and minimal detectable change (MDC).These details enhance the article's credibility and utility in clinical and research settings.

Conclusion and Implications:
The conclusions drawn in the revised version are more explicit about the implications of the findings.It emphasizes how the NDI-Hi can improve patient care and research outcomes specifically in rural areas with Hindi-speaking populations, aligning with broader healthcare needs and addressing specific linguistic and cultural barriers.
Any further responses from the reviewers can be found at the end of the article for the process of cross cultural adaptation of self-reported measures (Beaton et al., 2000) and most of the psychometric properties analysis, dimensionality factor analysis, responsiveness (MDC, Minimal Detectable Change) were are neither performed nor mentioned, living behind a methodological gap that has led to considerably decreased utility of Hindiversion of NDI in research and clinical set up.Further, there is compelling evidence from a review that this published work lacks methodological quality in the process of translation, which implies conduction of further research to develop a reliable, validated, and tested Hindi version of NDI.In addition, the previous version also has no mention of permission from the original author of the NDI tool (Pellicciari et al., 2016).It is essential to prioritize the efforts of translation and adaptation to understand cultural norms, attitudes, and behaviors with the objective to increase inclusivity in healthcare settings and research.Additionally, it is required that the procedures for the comprehensive psychometric properties study and cross-cultural adaptation of self-reported measures, as advised by consensus-based standards for the selection of health measurement instruments, be followed (COSMIN) (Mokkink et al., 2010(Mokkink et al., , 2016)).
As the occurrence of neck pain continues to rise and considering the populous native Hindi speakers, having a wellvalidated Hindi version of the NDI will enhance its clinical applicability and, most significantly, foster the inclusion of Hindi-speaking individuals suffering from neck pain in rural India but lacking proficiency in the English language.
Therefore, this study intended to translate and adapt the original version of NDI into Hindi and assess its psychometric properties among the Hindi-speaking people with chronic non-specific neck pain (CNSNP).Furthermore, objectives include translating NDI into the Hindi language and testing the Hindi version of the NDI for its reliability and validity and responsiveness among patients with CNSNP.

Methods
This methodological study used cross-sectional adaptation and validation method approach to develop NDI-Hi version.Permission to develop a new Hindi version among the rural Hindi speaking population was secured from the eprovide MAPI research trust, a non-profit organization based in France, and the copyright holder of the NDI through a signed agreement with the PI (MS).The study adhered to the SAGER guidelines for reporting sex and gender information.Sex and gender differences were not taken into consideration for the design of the study (Heidari et al., 2016).

Ethical approval
The translation, adaptation, and psychometric testing of the Hindi version of NDI was performed for the tool requirement of a subsequent registered clinical trial among Hindi speaking rural North Indian population.The present study was phase 1 of the clinical trial and includes a different study population.This study was approved by the Institutional Review Board of the Madhav University, Rajasthan (Ref.No: MU/IEC/21/14; dated 24/07/2021), and written informed consent for participation was obtained before patient recruitment.All procedures were conducted in accordance with the declaration of Helsinki.The purposes and the importance of the study were clarified to each participant.Participants were free to refuse to participate or answer any of the questions throughout the course of the study to ensure data confidentiality at all levels of the study, names of participants and any personal identifiers were not included.This study was part of larger trial that was registered prospectively with CTRI/2021/08/036040.

Participants
This study was conducted at the Physiotherapy outpatient department (OPD) of Sanskriti University Mathura, India and Jeevan Jyoti Hospital Mathura in the Northern State of India (Mathura city, Uttar Pradesh) from August 2021 to June 2022.Hence, the study protocol was presented to the Ethical member at the Madhav University and approval obtained.Further, the Ethical approval letter and the study proposal was submitted to the Clinical Trial Registry of India (Government of India) CTRI, which verified the application and granted permission to conduct the definitive study.
The study settings are the associate centers of Madhav University, and proper permission was obtained from the two centers to conduct the study.A total of 220 participants with CNSNP were recruited across two centers, of which 211 participants (114 females and 97 males) completed all participant-reported socio-demographic data, clinical information using face to face interviews as the participants in general visit the study center for consultations and physical rehabilitation, hence we decided to use interview method to improve the quality of data collected.by trained assessors.Neck Disability Index -Hindi version (NDI-Hi) and Neck Pain and Disability Scale (NPAD) (Agarwal & Allison, 2006).This study followed recommendations of best practices for developing and validating scales (R. Article, 2017), which suggests at least 5-10 participants per item in the tool as recommended by the COSMIN checklist (Mokkink et al., 2010).
Considering the lack of specific guidelines and different authors used different formula to estimate sample size like; factor analysis formula, Kaiser-Meyer-Olkin sampling adequacy (values ranging from 0.50 to 0.60), regression formula and item-sample ratio estimation (Arafat & Chowdhury, 2016).We intended to include all eligible patients with CNSNP attending both the study center's during the study period to improve the statistical estimations and consistency of the results.

Inclusion and exclusion criteria
Individuals aged 18 years and above, living with CNSNP for > 3 months duration, residing in rural area, who understand and speak Hindi language, and those willing to participate were included in this study.Individuals with acute neck pain, diseases causing neck disability, previous cervical spine injury, prolapsed intervertebral disc disease, traumatic vertebral fractures, neck surgery, clinically recognizable cognitive impairment, pregnancy, and those who could not read and speak Hind were excluded from the study.Individuals with chronic non-specific neck pain visiting the study area primarily for other problems were also excluded.

Instruments
Neck Disability Index (NDI) The NDI, originally developed by Vernon and Mior (Vernon & Mior, 1991) is a 10-item or section patient-reported outcome measure designed to assess neck pain and pain-related disability.The tool consist of 10 sections designed to selfreport on how neck pain impacts the activities of daily life, the domains are; intensity of pain, personal care (dressing, washing), lifting heavy and light weights, reading, headaches, concentration, work, driving, sleeping, and recreation.
Each section consists of six activity-based exclusive responses expressing progressive levels of functional disability.Item scores range from 0 (no disability) to 5 (total disability) and Vernon also established categorization of scores as; 0 to 4 no disability, 5 to 14 mild disability, 15 to 24 moderate disability, 25 to 34 severe disability, and ≥ 35 complete disability.The total score is out of 50 (Vernon & Mior, 1991) and is also frequently normalized to 100 and reported as a percentage.
The NDI (one-dimensional questionnaire) measures a single construct, and the questionnaire has demonstrated moderate differences in validity and reliability with a different patient population (Pietrobon et al., 2002).

Neck Pain and Disability Scale (NPAD)
The NPAD scale is a 20-item multi-dimensional questionnaire designed to assess neck pain and disability.The items are scored along a 10 cm visual analog scale (VAS) with the scores ranging from 0 to 5 in VAS.A higher score indicates greater disability.The Hindi version of NPAD has been cross-culturally translated and validated among 64 Indian individuals with cervical radiculopathy.The Hindi version of NPAD has been psychometrically tested and shown to have acceptable internal consistency and validity (Agarwal & Allison, 2006).

Translation and cross-cultural adaptation process
Tool adaptation and translation was conducted as per the guidelines suggested by Beaton et al. (2000).The translation and adaptation process for NDI consists of the following steps; forward translation, synthesis, backward translation, expert committee review, and synthesis, tool pretesting, and submission and appraisal of the written reports by the translationadaptation coordinating committee (Beaton et al., 2000).In step one, forward translation was performed from English to Hindi language by two Hindi native translators (a professional translator and a post-graduate employee working in education department) who were fluent in the English language.One independent translator was blinded to process of forward translation of NDI.This was done to make sure the equivalency from a therapeutic point of view rather than literal equivalence.The other translator was informed about the purpose of the study and the concepts being studied.This was for contemplating the language used by the population and spotlight terms in the original questionnaire, the translation of which might have been obscure.Two forward-translated documents (T1 and T2) were produced.In step two, the independently translated T1 & T2 documents were shared among the two translators to synthesize NDI-Hi (version 1).Any inconsistencies, differences in the concepts and/or meaning, elusive wordings were sorted by discussion and agreement.In step three, the first draft NDI-Hi was back-translated to English language by two bilingual independent translators (native Hindi language speaking teachers with master's degree in English) and not familiar with the construct being assessed and blinded to the process of forward translation.After discussion and agreement between back translators and the principal investigator (MS), a third translation was performed.In step four, all three documents were presented to the expert panel for review and discussion.The expert committee was comprised of four translators, two review committee experts from the university and two senior physiotherapy academicians who reviewed the Hindi version of the questionnaire.The panel discussed clarity, relevance, modifications, comprehension and synthesized the pre-final version for field testing Figure 1.

Pilot study and modifications
In step five, upon approval of the panel, NDI-Hi was piloted on 30 individuals with CNSNP (19 females and 11 males).
A cognitive (qualitative) debriefing and the pretest pilot of the pre-final NDI-Hi was conducted to assess; 1.The time taken to complete the tool and clarity of the instructions in the tool (administration).2. Internal consistency, if the items are logically ordered, necessity of the items in the tool (organization).3.If the questions are direct, whether the questions are free from technical jargon, cultural appropriateness.As a result, the majority of participants reported a good understanding of the tool.However, 16 participants reported section eight 'driving' not applicable to them.Based on cognitive debriefing comments made by the participants, the committee agreed to reword section eight (driving) to fit the cultural context in India where most people do not drive car, rather travel by public and/or private transport and motorbike.For the participants who did not answer/drive, the total score was adjusted from 45 instead of 50 (multiplying 50/45).The final Hindi version of the NDI was then compared with the original one to achieve representational, factfinding and contextual equivalence.
Psychometric testing of the NDI-Hi Psychometric properties were assessed using the final version of the NDI-Hindi (Sidiq, 2023) on 211 patients with CNSNP for > 3 months duration across three centers.The test-retest reliability of the NDI-Hi version was determined by calculating Cronbach's alpha with an alpha value of > 0.7 (deemed acceptable), > 0.8 (considered good), and > 0.9 (considered excellent) to grade the internal consistency (Taber, 2018).The minimum sample size required for two-tailed Cronbach's alpha test was calculated using the Bonet formula based on assumptions; item in the scale (k) 10, power 0.90 (1 -β), type I error (α) 0.05, value of Cronbach's alpha at null hypothesis (CA0) and expected value of Cronbach's alpha  et al., 2003).This is more than the power calculated sample.
To determine the dimensionality of the NDI-Hi, a stepwise exploratory factor analysis (EFA) was performed with Kaiser Meyer Olkin and Bartlett's criteria with a retention rule of an Eigenvalue > 1 (items with loadings ≥ 0.4 were considered satisfactory).Independent factors were obtained with maximum likelihood using the Varimax rotation model.The floor and ceiling effects, distribution and completeness of items responses and missing values were examined for content validity.The concurrent validity method was used for the criterion-related validity; Pearson's correlation analysis was done to establish relation between NDI-Hi and Visual Analogue Scale (VAS).The convergent construct validity was examined by comparing the NDI-Hi and Hindi version of NPAD using Spearman rank correlation coefficient (r).The r value of > 0.80 were considered excellent, and 0.61 to 0.80 very good.It is expected that the Hindi versions of NDI and NPAD would have moderate correlations since both tools measures the impact of neck pain on the functional status of the patients (Agarwal et al., 2006).Standard error of measurement (SEM) was calculated from the square root (SEM = SD √ (1-R)) of the within-subject variance from ANOVA for random-effect to evaluate the measurement error.MDC 95% was derived using the SEM to allow expression of the smallest magnitude of change that reveals the true change rather than measurement error by using the formula MDC 95% = 1.96 √2x SEM or 2.7*SEM.The Bland-Altman plot was also used to determine agreement (Bland & Giavarina, 2015) (Figure 2).

Statistical analysis IBM SPSS Statistics (RRID: SCR_016479
) version 20 was used to analyze the data (SPSS 20, IBM, Armonk, NY, USA).Characteristics and observations of the quantitative and qualitative variables were summed using the mean, standard deviation (SD) and frequencies or relative frequencies.Normality of scores from different instruments was examined using one-sample Kolmogorov-Smirnov test.Internal consistency, test-retest reliability, and convergent validity of the two scales used in the analysis were examined.The raw score of the NDI was transformed to 100 prior to psychometric testing of the tool.Authors in the present study were able to determine the internal consistency of the NDI-Hindi using Cronbach's alpha index with values between 0.70 and 0.90 considered satisfactory.For test-retest reliability, interclass correlation coefficients (ICCs) and 95 percent confidence intervals (CIs) were determined.ICCs below 0.40 were considered low, those in the range of 0.4-0.70 were considered moderate, 0.70-0.90was considered significant and values above 0.9 were considered exceptional respectively.The degree of correlation between NDI-Hindi and the NPAD at baseline was determined using Spearman's rho correlation.The significance level was set at P < 0.05.Using the scree test plot, retention rule (item value) of Eigenvalue > 1, and Kaiser Meyer Olkin (KMO) and Bartlett's test of sphericity, the dimensionality of the NDI-Hi was ascertained.The Maximum Likelihood with a Varimax rotation model was used for the EFA of the Hindi version of NDI, and the 0.4-factor loading principle was used for extraction (Zhang, 2015).

Participants
Demographic variables of the participants have been tabulated in Table 1 (Sidiq et al., 2023).All participants were assessed for their body mass index, duration of neck pain, pain medication, associated medical condition, marital status, employment status, level of education, income and mean and SD scores of NDI and NPAD.The majority of participants were female (n = 149, 70.6%), married (n = 152, 72.0%) and unemployed (n = 120, 56.9%).Near about 80% of the participants reported living with neck pain for 6 months and more.
Participant's response to NDI-Hi Table 2 displays the mean scores extracted from the participants in 10 sections of the NDI-Hindi.Participants were moderately affected due to neck disorder and the mean rating on NDI was 32.02 (6.9) out of 50 in total.Principle component analysis revealed two-factor structures (physical dysfunction and neurological dysfunction) of NDI-Hindi.
The physical dysfunction included pain intensity personal care, lifting, work, driving, reading and recreation were moderately to severely affected with a mean score ranging from 3.36-3.92,while neurological dysfunction that included headaches, concentration and sleeping were mildly affected with mean scores 2.3 and standard deviation of 0.6.

Internal consistency of the NDI-Hi
The Cronbach's alpha reliability was 0.962, which indicated that respondents were able to read and comprehend the 10 NDI-Hindi items well.However, all 10 indicators demonstrated a meaningful adjusted total association with their total scores.When these indicators were removed from the total, all of the items exhibited a corrected item-total correlation greater than 0.75, showing reasonably substantial shared covariance (Table 3).

Test-retest reliability of NDI Hi
Test-retest reliability was assessed seven days after the initial assessment and was found to be excellent.The test-retest reliability was excellent for the overall NDI-Hindi and average Interclass correlation coefficient (ICC) was 0.893, with a 95% Confidence interval (CI) (0.795, 0.937) (p < 0.001) (Table 2).The mean of item variances was 0.648, with inter-item covariance's mean of 0.465 (Table 3).

Construct validity of NDI-Hi
Construct validity of the NDI-Hindi was estimated using principal component analysis (factor analysis) with varimax rotation (Table 4).Data met the assumptions (Kaiser-Meyer Olkin = 0.826) of sample adequacy and Bartlett's test of sphericity.The total variance explained by two factors was 87.5%.The analysis found a two factor structure of scale; Factor 1 included the first seven items of the questionnaire (77.3% of variance), Factor 2 included three items (10.2% of variance) (Table 5).Factor loading was determined using a scree plot (Figure 3).

Convergent validity of NDI-Hi
The scores of NDI-Hindi showed excellent correlation with the total scores on Hindi-validated version of NPAD scale.Scores on neck pain and disability scale showed a significant positive correlation with all 10 items of NDI, with the  highest correlation with lifting item (0.917, p = 001) and a least but significant correlation with the concentration item and sleeping (0.845, p = 0.001) (Table 6).

Discussion
This study aimed to translate and adapt the original English version of NDI into the national language of India (Hindi) and test the psychometric properties of the NDI-Hi version.Specifically, this study aimed to address the methodological gap of the previous Hindi version of the NDI (Hung et al., 2014;Patel, 2012;Pellicciari et al., 2016) with improved statistical estimation using the recommended best practices for developing and validating scales.The previous study which aimed to adapt, test-retest the reliability, and validate the Hindi version of NDI demonstrated methodological shortcomings like non-reproducible methods, and not complying with the required translation steps for cross-cultural validity.The published version of the previous article reported only findings about the internal consistency (α 0.995), and test re-test reliability (ICC, 0.99).Further, it noteworthy that the commonly used NDI raw score is not linear and should likely not be used in interpretation (Hung et al., 2014).Hence, it is recommended to transform the raw NDI score into a linear measure (convert to 100) prior to data analysis.The lack of methodologies related to score transformations, hypothesis tested, dimensionality, and testing of validity in the previous work did not permit a meaningful comparison with findings of this study.
The recommended guidelines were followed during translation and adaptations (Beaton et al., 2000).The translation, adaptation, and synthesis of NDI-Hi was easy and accepted by the Hindi speaking people with CNSNP.Overall findings from this study indicate NDI-Hi to be a reliable and valid patient-reported outcome measure that could be used by researchers and clinicians to assess disability and functional limitations caused by neck pain among the Hindi-speaking population who are unable to read or write in the English language.
NDI-Hi demonstrated excellent internal consistency and Cronbach α of 0.89, which is comparable to the reports of previous works (0.74-0.97) and explains sample adequacy (Wu et al., 2010).In this study, the time interval for the testretest re-administration was set at 48 hours, which is a minimum duration that is likely to result in minimal alterations in the patient's clinical condition and minimal memory-related effects (Marx et al., 2003).Likewise, NDI-Hi also showed good internal consistency, indicating good reliability.The acceptability of the NDI-Hi showed that all the items were below the threshold recommended for floor effects (20%).However, the ceiling effect of the pain intensity was found to be marginally (21.6%) higher than the threshold recommended.Similarly, previous studies reported no floor or ceiling effects with the only exception being the intensity of pain (Nakamaru et al., 2012;Shashua et al., 2016;Trouli et al., 2008;Farooq et al., 2017).Though this phenomenon is not unique, a study on the Malay version of NDI reported moderate responsiveness of pain intensity and also explains the complexity in quantifying pain (Lim et al., 2020).
In our study, the pilot test conducted to check the feasibility and acceptability of the translated NDI-Hi version found that the majority of participants were not responding to the item on driving and the same was discussed in the cognitive debriefing.In India, the majority of individuals travel using motorbikes, public transportation, and private vehicles, with a relatively small portion choosing to commute by car.Moreover, when section eight, which pertains to driving, is culturally adapted to encompass driving, riding, or traveling, it significantly enhances the responses to this section, reducing the occurrence of missing values related to driving in various studies (Cook et al., 2006;Lee et al., 2006).SEM (< 0.4) and MDC 95% of the NDI-Hi version indicated an absolute reliability and genuine agreement of repeated measurements, and suitability of NDI-Hi for clinical and research uses.MDC 95% of 7.15 (score range 0-50) will guide clinicians and researchers of true change in NDI-Hi scores.Scores at or above MDC value indicate meaningful clinical change in patients.MDC value of NDI-Hi is comparable to the values reported by other researchers and smaller (precise) than other studies (Pool et al., 2007;Young et al., 2009;Trouli et al., 2008;Farooq et al., 2017;Maki et al., 2014;Shashua et al., 2016).The smallest detectable change (SDC) and minimally important difference (MIC) reported by the Dutch version was 11.5, and 31.7 respectively, the Italian version NDI showed MIC of 10, and a methodological review conducted including 19 NDI versions reported only these three versions of NDI mentioned MIC (Yao et al., 2019).The MDC reported in this study is 7.15, which is relatively lower than MDC reported elsewhere, and this is suggestive that even a smaller change in the Hindi version of NDI shall be considered as an important yardstick of clinical relevant hence, offers a sensitive outcome tool even in case of less powered sample or individual level studies.
The validity of NDI-Hi was conducted by qualitative cognitive debriefing to establish content validity and correlation test of the scale with the NPAD Hindi version to evaluate the construct convergent validity (Brod et al., 2009).Based on the pilot study and cognitive briefing, rewording of item eight was done, which improved the understanding, acceptance and response rate.Factor analyses resulted in a hypothesized 2-factor solution for NDI-Hi represented as physical dysfunctions and neurological dysfunctions.These factors explained 69.51% of the total variance, and the variance reported was comparable to some previous studies (Nakamaru et al., 2012).The Hindi versions of NDI and NPAD appear to measure a similar construct.The NDI is a condition-specific patient-reported outcome measure (PROM) and it is frequently used in researches exploring intervention efficacy among individuals with neck pain.Similarly, psychometric properties of NDI-Hi propose it as a suitable PROM for Hindi-speaking individuals with neck pain.Nonetheless, suitability of NDI in patients with whiplash injury, social and emotional is questioned by Hoving et al., highlighting limitation of the NDI that lacks elements to address these problems (Hoving et al., 2003).The prospects of implication of the NDI-Hi include; improved reporting of disability related to neck pain among the most populous Hindi speaking Indian people.Improve the use of the new NDI-Hi in the clinical set-up to assess and track the changes related to self-reported disability among chronic neck pain patients.

Study limitations
This study recruited samples beyond the recommended guidelines for cross-cultural adaptations of outcome measures and the required power calculated sample for test-retest reliability, which improved the statistical power of the psychometric evaluation of the NDI-HI version.However, there are few limitations to mention; this study is a crosssectional design and hence any correlations should not be interpreted as causal effects.This study used only a selfreported questionnaire, the relationship between the activity limitations of neck pain (NDI) and physical tests were not considered and the study was done among rural northern Indian population only.

Conclusions
The English version of NDI was successfully adapted to suit the rural Indian cultural context and translated to the Hindi-India version.The Hindi version of the NDI-Hi tool has healthy psychometric properties and appears to be suitable for use in epidemiological studies and clinical trials among Hindi language speakers.The key feature of the NDI-Hi being its content related to rural people and culture specific and the new NDI-Hi version promises to be a comprehensive tool for measuring disability among rural Hindi speaking people.
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

Authors' contributions
Conception and design was presented by: MS, AR, Acquisition of Data: BJ, JS, PCH, Analysis: BJ, FK, PK.MS, AR, BJ, and FK drafted the work, AC, PK, AR, YA, SPC, RM, PK and AAAM, JS did critical revision and all authors gave final approval to the version to be published.The abstract provides a succinct overview of the study.However, it can be improved by adding more specific details to give readers a clearer understanding of the study's significance and outcomes.The background should specify the importance of validating the NDI for rural Hindispeaking populations and how this fills a gap in current research.The methods section should detail the translation process more concisely, emphasizing the steps involved.The results section should highlight key statistics like the ICC, Cronbach's alpha, SEM, MDC, and correlation coefficients.Finally, the conclusions should reinforce the clinical applicability and importance of the NDI-Hi in rural settings.

Introduction:
The introduction effectively outlines the prevalence and impact of non-specific neck pain globally and in India, providing a solid rationale for the study.To enhance it further, include more recent statistics and studies to underscore the growing burden of neck pain.Highlight the unique challenges faced by rural populations in India, such as limited access to healthcare and language barriers.Additionally, the introduction should emphasize the importance of culturally adapting the NDI to ensure its relevance and accuracy for Hindi-speaking patients.This sets a clear context for the need for the NDI-Hi and its potential benefits.

Methods:
The methods section is comprehensive, detailing the translation and adaptation process meticulously.To improve clarity, consider breaking down the translation steps into sub-sections with clear headings for each stage: forward translation, synthesis, backward translation, expert committee review, and pilot testing.This would make the process easier to follow.The section on psychometric testing should provide more detail on the statistical methods used, such as the criteria for factor analysis and the rationale for the selected time intervals for test-retest reliability.
Including a flowchart summarizing the entire process could also enhance clarity and readability.

Results:
The results section presents the findings effectively, with detailed statistical analysis.To make it more impactful, provide more context for the statistical figures, explaining what they mean in practical terms.For instance, elaborate on how the high Cronbach's alpha and ICC values demonstrate the reliability and validity of the NDI-Hi.Include more descriptive statistics and graphical representations, such as bar charts or histograms, to visually summarize the data.Additionally, the demographic characteristics of the participants should be discussed in relation to the findings, highlighting any significant correlations or trends.

Discussion:
The discussion appropriately interprets the results, linking them back to the study's objectives and existing literature.To deepen the analysis, compare the psychometric properties of the NDI-Hi with those of other versions used in different cultural contexts.Discuss any unexpected findings or limitations encountered during the study, such as the challenges related to the driving item.Propose potential solutions or areas for future research to address these limitations.Furthermore, emphasize the clinical implications of the NDI-Hi, particularly how it can improve patient outcomes and research quality in rural Hindi-speaking populations.

Conclusion:
The conclusion succinctly summarizes the study's findings and their significance.To enhance it, reiterate the key strengths of the NDI-Hi, such as its high reliability and validity.Highlight the broader impact of having a validated Hindi version of the NDI, such as its potential to inform public health policies and improve clinical practices in rural India.Additionally, suggest specific applications of the NDI-Hi in both clinical and research settings, emphasizing its role in enhancing the understanding and management of neck pain among Hindi-speaking populations.

Is the work clearly and accurately presented and does it cite the current literature? Partly
Is the study design appropriate and is the work technically sound?

Introduction
The introduction contains a good number of facts and findings, but it looks jumbled up and it doesn't properly lead to the need for the study.This can be improved by properly articulating the facts.

Methods
This study is mentioned as a cross-cultural study that has studied the adoption and psychometric evaluation of the NDI scale, But it is mentioned as an observational study.This has to be cross-checked as cross-cultural studies are not purely observational studies and adoption and psychometric evaluations are mostly methodological studies.This has to be clarified.

1.
How was the sample size estimated?2. The data was collected from the subjects after 48 hours, and some justification was given in the discussion.Please provide the evidence for this.Has any evidence suggested that collecting data in 48 hours can give a better outcome?If yes please do justify it in the methodology section also.

4.
The sample size to be used for psychometric evaluation and test-retest reliability has to be similar.However, there is a disparity between the numbers used.What is the justification for the change in sample size?

5.
It was mentioned that the gender-specific analysis was done.I couldn't find any analysis.6.
What was the purpose of the pilot study?7.

Results
Please align the tables corresponding to the findings.The current presentation makes it tough to correlate the findings. 1.

Discussion
The discussion can be made better by stressing the findings.This study was done on the shortcomings of the previous study.When the primary aim of this study was to address the shortcomings, the results can also be specific to those. 1.
This study has only reported internal consistency and validity, but the aim of the study was not at all discussed with facts and findings. 2.

References
Two studies with the author name "Study" are wrongly cited.1.

General Comments
The manuscript needs language editing and grammatical correction. 1.
There is a lack of coherence and cohesion throughout the text.2.

Are sufficient details of methods and analysis provided to allow replication by others? Partly
If applicable, is the statistical analysis and its interpretation appropriate?Yes Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: My area of expertise is musculoskeletal pain and cardiopulmonary rehabilitation I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
study.This has to be cross-checked as cross-cultural studies are not purely observational studies and adoption and psychometric evaluations are mostly methodological studies.This has to be clarified.How was the sample size estimated?2.
The data was collected from the subjects after 48 hours, and some justification was given in the discussion.Please provide the evidence for this.Has any evidence suggested that collecting data in 48 hours can give a better outcome?If yes please do justify it in the methodology section also.

4.
The sample size to be used for psychometric evaluation and test-retest reliability has to be similar.However, there is a disparity between the numbers used.What is the justification for the change in sample size?

5.
It was mentioned that the gender-specific analysis was done.I couldn't find any analysis.

6.
What was the purpose of the pilot study?7.

Authors' response
Thank you, as per the suggestion we have removed the observational study design.And amended changes related to the methods used (methods, lines 135-136). 1.
Considering the lack of specific guidelines and different authors used different formula to estimate sample size like; factor analysis formula, Kaiser-Meyer-Olkin sampling adequacy (values ranging from 0.50 to 0.60), regression formula and item-sample ratio estimation We intended to include all eligible patients with CNSNP attending both the study center's during the study period to improve the statistical estimations and consistency of the results.(Methods section, lines 165 -171).A total of 220 respondent consented and 9 participants either did not complete the questionnaire or the data sheet was not complete.

2.
The figure 1 is changed now accordingly 3.
Thank you for the suggestion, we have amended the changes accordingly (Methods section; lines 262 -265) 4.

1.
"test-retest re-administration was set at 48 hours, which is a minimum duration that is likely to result in minimal alterations in the patient's clinical condit110ion and minimal memoryrelated effects (Marx et al., 2003).Yes, considering the difficulty and constraints (response rate) in inviting the respondents to attend face to face interview prospectively for the 2 nd time, we used the recommended "minimum sample size required for two-tailed Cronbach's alpha test was calculated using the Bonet formula based on assumptions" .Hence, testretest was conducted using n = 110.The same was prospectively informed and approved by the MAPI Research Trust.
Thank you for pointing out, we have removed the statement now. 1.
The purpose of Pilot study and cognitive debriefing is now mentioned in the method section (lines 235 -242).

Results
Please align the tables corresponding to the findings.The current presentation 1.
makes it tough to correlate the findings.Authors' response Changes done accordingly, thank you

Reviewer 1 comment Discussion
The discussion can be made better by stressing the findings.This study was done on the shortcomings of the previous study.When the primary aim of this study was to address the shortcomings, the results can also be specific to those. 1.
This study has only reported internal consistency and validity, but the aim of the study was not at all discussed with facts and findings. 2.

Authors' response
Yes, thank you for reminding us of our primary purpose of addressing the methodological gap of previous work. We

References
Two studies with the author name "Study" are wrongly cited.1.

Authors' response Done accordingly
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Figure 2 .
Figure 2. Bland-Altman plot of agreement between test and re-test scores of NDI-Hi.Bold blue line representing the mean of difference, the red lines representing 95% LOA and the grey lines representing the 95% CI of the mean of the difference.NDI-Hi, Hindi-version of the Neck disability index; LOA, limits of agreement.

Figure 3 .
Figure 3. Scree plot indicating factor loading for NDI-Hi.NDI-Hi, Hindi-version of the Neck disability index.
Evaluation of the Hindi Version of Neck Disability Index in the Rural Population of Northern India: A Cross-Cultural Study Abstract:

Table 1 .
Socio-demographic and clinical characteristics of participants with CNNP for psychometric testing (n = 211).
CNNP, chronic non-specific neck pain; NDI-Hi, Hindi-version of the Neck disability index; VAS, visual analog scale.

Table 3 .
Internal consistency of the NDI-Hi if item deleted (n = 211).
NDI-Hi, Hindi-version of the Neck disability index.The overall Cronbach's alpha of 10 items was 0.962.

Table 5 .
Principle factor analysis for two components on the Varimax rotation for the NDI-Hi.
NDI-Hi, Hindi-version of the Neck disability index.Extraction Method: Principal Component Analysis.Rotation Method: Varimax with Kaiser Normalization (KMO).

Table 6 .
Spearman's rho correlations of the NDI-Hi with the sub scales of NPAD.
NDI-Hi, Hindi-version of the Neck disability index; NPAD, Neck Pain and Disability Scale.**Correlation is significant at the 0.01 level (2-tailed).*Correlation is significant at the 0.05 level (2-tailed).
have now amended the changes and added content according to your valid suggestions.(Discussion section, lines 353 -364) "it is important to the commonly used NDI raw score is not linear and should likely not be used in interpretation.Hence, it is recommended to transform the raw NDI score into a linear measure (convert to 100) prior to data analysis.The lack of methodologies related to score transformations, hypothesis tested, dimensionality, and testing of validity in the previous work did not permit a meaningful comparison with findings of this study".Reference; Hung M, Cheng C, Hon SD, Franklin JD, Lawrence BD, et al.Challenging the norm: further psychometric investigation of the Neck Disability Index.Spine J. 2015.doi:10.1016/j.spinee.2014.03.027.And, the same is mentioned as well.Please suggest us if the content added is justifying.Thank you again for pointing out.