Agreement between Original and Rasch-Approved Neck Disability Index

doi:10.21203/rs.3.rs-18446/v2

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Agreement between Original and Rasch-Approved Neck Disability Index

https://doi.org/10.21203/rs.3.rs-18446/v2

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published 03 Jul, 2020

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Background: Given the high prevalence of neck pain, the neck disability index (NDI) has been used widely to evaluate patient status and treatment outcomes. Modified versions have been proposed as solutions to measurement deficits in the NDI. However, the original 10-item NDI scored out of 50 is still the commonly administered. Examining the extent of agreement between traditional and Rasch-based versions using Bland-Altman (B&A) plots will inform our understanding of score differences that might rise from using different versions. Therefore, the objective of current study was to describe the extent of agreement between different versions of NDI.

Methods: The current study was a secondary data analysis where the study data was compiled from two prospectively collected data source. We performed a comprehensive literature search to identify Rasch-approved NDI within four databases including Embase, Medline, PubMed, and Google Scholar. Modified version to identify Rasch analyses which provided alternative forms and scoring. We graphed B&A plots and calculated the mean difference and the 95% limits of agreement (LoA; ±1.96 times the standard deviation).

Results: Two Rasch approved alternative versions (8- and 5- item) were identified from 303 screened publications. We analyzed data from 201 (43 males and 158 females) patients attending community clinics for neck pain. We found that the mean difference was approximately 10% of the total score between the 10-item and 5-item (-4.6 points), whereas the 10-item versus 8-item and 8-item versus 5-item had smaller mean differences (-2.3 points). The B&A plots displayed wider 95% LoA for the agreement between 10-item and 8-item (LoA: -12.0, 7.4) and 5-item (LoA: -14.9, 5.8) compared with the LoA for the 8-item and 5-item (LoA: -7.8, 3.3).

Conclusion: Two Rasch-based NDI solutions (8 vs 5 items) that differ in number of items and conceptual construction are available to provide interval level scoring. They both scores that are substantially different from the traditional ordinal NDI, which does not provide interval level scoring. Smaller differences between the two Rasch solutions exist and may relate to the items included. Due to the size and unpredictable nature of the bias between measures, they should not be used interchangeably.

Health Economics & Outcomes Research

Orthopedics

Original

Rasch-Approved

Neck Disability Index

Neck pain is considered a notable social burden and has a high point prevalence (33%) within the adult population, and nearly 70% of peoples will experience neck pain at some point during their lifetime (Bovim, Schrader, & Sand, 1994; Covic, Pallant, Conaghan, & Tennant, 2007; Croft et al., 2001; Hogg-Johnson et al., 2008; MacDermid et al., 2009). Clinical decision-making requires monitoring the treatment effect (improvement or deterioration) from both clinician and patient perspectives. The first patient-reported outcome measure (PROM) assessing pain and disability in participants with neck pain was published in 1991 – the neck disability index (NDI)(Vernon & Mior, 1991). The NDI is the most studied neck-related, cited and applied in more than 300 publications (Vernon, 2008). It has been used widely in surgical treatment, injection therapies, physiotherapies, as well as the exercise and research context (Iyer et al., 2019; MacDermid et al., 2009; Vernon, 2008). A systematic review (MacDermid et al., 2009) and an overview (Bobos, Macdermid, Walton, Gross, & Santaguida, 2018) have reviewed a large volume of psychometric evidence with most studies suggesting the NDI has a excellent psychometric properties and a minority raising concerns about factor structure, item relevance or scaling. The original version of the NDI has been translated into 22 languages versions (Evans et al., 2012; Vernon, 2008).

The NDI was developed as a unidimensional instrument assessing neck disability, with this as a fundamental requirement for using a single summary score (Packham & Macdermid, 2013; Pallant & Tennant, 2007; Van Der Velde, Beaton, Hogg-Johnston, Hurwitz, & Tennant, 2009). The NDI contains 10 items including pain intensity, personal care, lifting, reading, headaches, con- centration, work, driving, sleeping, and recreation. Each item has 6 response options ranging from 0 to 5, where 0 represents the best situation and 5 represents the worst. Individual scores are summed to derive a total score from 0 to 50 with a higher score indicating the more serious level of disability. Multiple items ask about pain and function together, which we consider is more representative of the construct pain-related functional interference. Through the problem elicitation technique (PET), others have concluded that the NDI is a multidimensional scale that measures symptoms, impairments, and disabilities (work, recreation) (Hoving, O’ Leary, Niere, Sally, & Buchbinder, 2003).

Previous researchers have examined original NDI using factor analysis, qualitative interview, and construct analysis under the classical test theory (CTT) (Hung et al., 2015). Gabel et al (2014) concluded that the NDI is a one-factor model confirmed by confirmatory factor analysis in a homogenous population with neck pain. However, others identified 2 factors using a principal component analysis (Wlodyka-Demaille et al., 2004).

Rasch analysis based on item response theory (IRT) and Rasch modelling enables examination of unidimensionality and interval level of scaling, and can lead to a transformation strategy to convert an ordinal score to interval scaling, which can validate the use of a total sum score (Cano, Barrett, Zajicek, & Hobart, 2011). Where outcome measures are not developed using Rasch modelling, they can retrospectively be evaluated for fit to the Rasch model which often results in suggested modifications needed to obtain fit. Several studies have inspected the NDI using Rasch analysis and found violations of Rasch basic assumptions (Gabel, Cuesta-Vargas, Osborne, Burkett, & Melloh, 2014; Van Der Velde et al., 2009; Walton & MacDermid, 2013). They offered solutions which included exclusion of misfit items and new coding algorithms. Although modified versions of NDI have been constructed that are conceptually and statistically sound, uptake has been limited and the traditional NDI is still commonly used. Studies to date have focused on defining modified versions with better measurement properties but have not defined the extent to which these new versions differ from the traditional NDI scoring outside of the development data set. Examining the amount of agreement between traditional and Rasch-based versions of the NDI using Bland-Altman (B&A) plots will inform our understanding of how these scores might differ (Bland & Altman, 1999, 2010; Nazari, MacDermid, Sinden, Richardson, & Tang, 2019)

Therefore, the objective of current study was to describe the extent of agreement between different versions of NDI in a sample of patients attending community clinics for neck pain.

Study design

The current study was a secondary data analysis where the study data was compiled from two prospectively collected data source. Both studies received ethical approvals (McMaster REB #03-145 and HiREB #13-300) and all participants provided written, signed consent. Participants were recruited from community clinics presenting for neck pain in Hamilton, ON Canada through paper and online based survey.

Information source

We performed a comprehensive literature search to identify Rasch analyses of the NDI within four databases including Embase, Medline, PubMed, and Google Scholar. Search keywords were set as neck disability index, NDI, Rasch analysis, structural validity, construct validity. The search year range was limited until January 2020. Details of search strategies were presented in Appendix 1.

Eligibility Criteria

We included studies that applied the Rasch model to evaluate the structural validity of NDI. According to assumptions of the Rasch theory, we defined the acceptable fit of the Rasch model as followed

The confirmation of unidimensionality.

E.g. In studies using the Rasch analysis software, RUMM2030 (Rumm Laboratory, Australia) we used the common criterion that acceptable unidimensionality is present if the number of the significant tests is less than 5% of the overall paired sample t-tests (Pallant & Tennant, 2007).

Overall test-fit statistic examined by the Chi-square test; a non-significant p-value was acceptable.
Where response categories are not distinct or clear, this can show up as disordered thresholds. Where this is the case, strategies such as collapsing the adjacent response options can be used as corrective actions, and the rescoring structure should be reported and used to calculate revised NDI scores.
There was no differential item functioning (DIF) existing including both uniform and non-uniform DIF in the revised version.
Assessment of local dependency within the item set, with scale amendments taken where appropriate.
We adopted an appropriate level of the person separation index (PSI) (PSI > 0.7)

Data Extraction

The score transformation algorithm was obtained if the revised version achieved an acceptable level of model fit identified by the eligibility criteria

Study Selection

An independent reviewer (ZL) performed the systematic electronic searches in all the databases. ZL also identified and removed the duplicate studies. The independent reviewer then carried out the screening of the titles/abstracts and identifying the full text articles. One author [JMacD] randomly reviewed 50% of the articles and discussed the disagreement with the first author to determine the final article eligibility.

Statistical procedure

The demographic statistics of the sample including age, sex, total score of all included versions of NDI were described by mean, standard deviation (SD), minimum and maximum value.

Agreement of Rasch solutions

The normal distribution of mean differences of all three comparisons were inspected by the histogram. Using the B&A plots, we summarized the individual agreement between each of the identified NDI versions by the mean difference and the 95% limits of agreement (LoA; ±1.96 times the standard deviation).

To test the average agreement and differences between each NDI score, we examined the mean differences by one-sample t-test. We reported the sample size for each comparison, the degree of freedom, mean differences, standard error of differences (SE), p-values, and 95% confidence interval (CI).

Transformation including logarithmic and linear transformation would be applied to normalize the non-uniform pattern of the bias on the plot. For instance, when the B&A plot shows a linear relationship between differences and means as the differences or measurement bias starts with negative value and then become positive while the magnitude of the mean increases, we can regress differences between the methods (D) on the average of the two methods (A) by D = b1 × A + b0. The 95% LoA for the regression should build on the SD of the residual (SDres) from the established model (±1.96 times SDres) (Bland & Altman, 1999).

All analysis was performed by IBM SPSS statistics, Version 25.0 (IBM Corporation, Armonk, NY). We considered a significance level of p ≤ 0.05 as statistically significant.

Study Selection and NDI version identification

Initially, our search yielded 303 publications. After removing the duplications, 296 articles were left. Six studies were then selected for full text review after title and abstract review. Of these, two Rasch solutions that met the study criteria were identified from 2 individual studies including a 8-item version developed by Van Der Velde and colleagues(Van Der Velde et al., 2009) which was based on Rasch criteria, and a 5-item version developed by Walton and MacDermid (2013) based on conceptual and Rasch criteria (Walton & MacDermid, 2013). This allowed 3 B&A comparisons (NDI-10 vs. NDI-8, NDI-10 vs.NDI-5, and NDI-8 vs. NDI-5). The flowchart of studies through the selection process is displayed in Figure 1.

Ordinal score transformation

Three NDI scores were calculated for each participant. The first NDI score was derived from the original ordinal scale (maximum of 50)(Vernon, 2008). We calculated second set of NDI scores according to the 8 item solution provided by Van Der Velde and collogues (Van Der Velde et al., 2009), where2 items (headache and lifting) were suggested to be deleted before summarizing individual item score. Afterwards, the ordinal scores were then transferred to linear score with the maximum value of 50. For third score transformation, two steps were taken to derive the total score according to the previous research (Walton & MacDermid, 2013). Firstly, 5 items regarding person care, concentration, working, driving, and recreation were kept into the total score calculation. A rescoring strategy, was then used to remedy the disordered threshold of driving related item (Walton & MacDermid, 2013). The original score of responses (012345) was re-coded by collapsing the fourth and fifth options (012334), while the original structure (012345) was retained for other 4 items. Therefore, the maximum total score of NDI 5-item version was 24 on the ordinal scale. This score was transformed in to an equivalent ranging from 0 to 50 to enable the direct comparisons (Walton & MacDermid, 2013). Please see Appendix 2 for a summary of transformations.

Sample

Table 1 describes the demographic information including age, pain intensity, total scores of NDI 10-item, NDI 8-item, and NDI 5-item version and stratified by sex. Thirty-one subjects experienced injury or trauma related neck-pain including car accident, sports injury, and fall. Other reasons are arthritis, pinched nerve, and disc problem. The normal distribution of the mean differences of comparisons were confirmed by inspecting the histogram. See Figure 2,3,4.

Agreement of Rasch solutions

Table 2 demonstrated both average and individual agreement results of all three comparisons.

Through pairwise comparisons, we identified the mean difference was approximately 10% of the total score between the 10-item and 5-item (-4.6 points), whereas the 10-item versus 8-item and 8-item versus 5-item had similar mean differences that were about half (-2.3 points). We considered the traditional 10-item as the reference method during comparisons, negative mean differences indicating that both 8-item and 5-item were systematically scored higher than standard 10-item version. The B&A plots displayed wider 95% LoA for the agreement between 10-item and 8-item (-12.0, 7.4) and 5-item (-14.9, 5.8) compared with the agreement of 8-item and 5-item (-7.8, 3.3).

Through visual inspection of the Bland-Altman plot, the bias between 10-item and 8-item tended to be in opposite directions at different point in the scale range, as negative value of differences predominated in the lower end (before scores of 20) and positive values predominated in the high end of the scale (between 20 and 40). A similar trend was identified in the comparison between 10-item and 5-item version. However, such patterns were not present in the plot comparing 8-item with 5-item version. Please see figure 5, 6, 7.

The linear relationship on the B&A plot comparing the 8- and 5-item version was confirmed by the simple linear regression equation D = -0.2 × A + 2.2 with a significant p value for the over model and regression coefficient (p < 0.001) (Bland & Altman, 1999). We then plotted 95% LoA based on the SDres which was equal to 2.4 from the regression model. The new upper and lower limited was constructed as D = -0.2 × A + 2.189 ± 1.96 × 2.4. Please see Figure 8.

We identified two Rasch approved versions of the NDI (8- and 5-item) through a comprehensive literature review and revealed disagreements within versions (10-item vs. 8-, and 5- item) using B&A plot analysis. (Giavarina, 2015; Van Der Velde et al., 2009; Walton & MacDermid, 2013).The wide range of the 95% LoA established surrounding the point estimate of the agreement would threaten the interchangeable application of different versions. When compared the traditional 10-item version with the 8-item Rasch version, a difference of ranging from -12.0 to 7.4 units accounting for nearly 15% to 25% of the total score was important for a measurement of 50 units, since 9 units of change would significantly influence the classification of the disability level(Vernon, 2008). For example, a participant who obtained a score of 20 on the traditional NDI would be considered to have moderate level of neck disability. However, the LoAs between Rasch versions suggest that scores might fall within the mild or severe level a range from -12.0 to 7.4 units. This reflect the extent of misclassification error that might occur on the basis of scoring. The bias between versions was even larger o 30% (-14.9 for lower limit) when comparing the traditional 10- with 5-item Rasch versions. The differences between 8- and 5-item version were uniform after linear transformation and were smaller than discordance between the traditional and Rasch scored versions, with a mean variation of 4.7 units (10% of the total score). This smaller difference likely reflects differences in items included, but still suggests that these measures cannot be used interchangeably. An advantage of the 8-item versions is that it 8 items may exhibit more range or stability than a 5-item version. Conversely, the 5-item version is more focused conceptually and reduces respondent burden. Head-to-head comparison of how these two versions performed in measuring clinical outcomes over time are needed to evaluate relative utility.

The unstable variance in error patterns on B&A plot were problematic for comparing across Rasch versions , even though they had small error limits (-2.3 and -4.6). Through visual inspection, the direction of bias reverted when the scores approaching 20 points, approximately mid-range . Attempts including both logarithmic and linear transformation failed to normalize the bias pattern. The more extreme bias displayed at the upper and lower ends of the scale is reflective of the ordinal nature of the original 0-50 score, whereas the 5 and 8-item versions have been linearly converted through the Rasch analytic process. This may explain why similar patterns were observed between the 10 & 8-item, and 10 & 5-item versions, but a different pattern was shown between the 5 & 8-item versions. Our study suggests that the original ordinal scale ranging from 0 to 50 should not be used in the parameter statistical analysis due to the violation of interval level scaling.

.The differences between the 5- and 8-item versions could be due to the variations in the retained items, both in terms of their content and the associated 'difficulty' level of the item. Firstly, fewer items are likely to result in a narrower measurement range coverage, and therefore the scale may be 'stretched out' when converted back to a 0-50 score. The two shorter Rasch-based NDI versions as may both be psychometrically valid, whereas the total 10-item score remains psychometrically dubious given the scaling problems identified by prior Rasch analyses .

The smaller differences between the 8-item and 5 item version may have been driven by methodologic differences in how these analyses were performed. In the 8-item version, the items (headache and lifting) were deleted to achieve the optimal model fit (Van Der Velde et al., 2009). For the 5-item version, the authors conducted a 2-stage process first deleting items for conceptual reasons and then proceeding to a Rasch analysis. The conceptual framework of the International Classification of Functioning, Disability and Health (ICF) was used to refine the item pool as to those that fit within the disability construct the symptom-based item such as pain intensity was removed at this stage (Walton & MacDermid, 2013). This retention of symptoms in the 8-item version and its exclusion from the 5-item version might result in small systematic errors between the scores. Researchers might determine the choice of 8- and 5-item NDI based on conceptual issues. For example, 8-item provides the evaluation of neck disability regarding pain intensity, sleeping, and reading. Conversely, the 5-item version focuses on function and would require that pain be measured in a different standardized measure, since this is clearly an important issue for people suffering from neck pain. The 5-item version might allow for clearer distinction between constructs, but the point at which measures become too short is not clear. Our qualitative work with patients with neck pain suggests that patients want comprehensive consideration of the broad array of life impacts that result from neck pain.

Finally, there is an update in terms of setting the acceptable level of the local independence which may resulting in the variation of constructing Rasch approved models since the examination of local independence is considered as one important test of assumption under Rasch modelling. Van Der Velde et al (2009) defined the critical residual correlation coefficient should larger than 0.3 to confirm the presence of LD, where as Walton and MacDermid (2013) adopted the criterion indicating LD is 0.2 above the average residual correlation, rather than the straight cuff-off of 0.3 (Christensen, Makransky, & Horton, 2017; Van Der Velde et al., 2009; Walton & MacDermid, 2013).

Despite the differences in different versions of the NDI and the concerns about the scoring of the full NDI, a benefit of e the complete 10-item version is that the score can be transformed into either modified version , whereas this is not the case if either of the 5- or 8-item version are administered (Van Der Velde et al., 2009; Walton & MacDermid, 2013).

Strengths & limitations

The literature review only examined studies published in the English language, which may limit the identification of potential Rasch solutions of NDI. The study sample was recruited from community clinics in a single city in Canada which restricts the generalizability of study findings.

Implications

Future studies should examine our study results on a generalize sample across multiple time points since we only analyzed the cross-sectional data from a community-based population. A consensus on the selection of different versions should be achieved by researchers and clinicians. Measurement of neck-related function seems to be a delightful direction for future research considering the disagreement found within three versions.

The traditional 10-item version should not be used interchangeably with other two Rasch-approved versions. Different coverage of content should be considered during the decision of 8- and 5-item NDI.

NDI: The neck disability index

B&A: Bland-Altman

PROM: patient-reported outcome measure

CTT: classical test theory

PET: problem elicitation technique

IRT: Item response theory

DIF: differential item functioning

PSI: person separation index

SD: standard deviation

SE: standard error

CI: confidence interval

SDres: SD of the residual

ICF: International Classification of Functioning, Disability and Health

Ethics approval and consent to participate: McMaster REB #03-145 and HiREB #13-300. All participants provided written, signed consent, the consent form will be submitted upon request.

Consent publication: All authors consent publication.

Availability of data and materials: The datasets during and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests: The authors report no conflicts of interest.

Funding: The authors report no funding.

Author’s contribution: ZL and JM conducted the systematic electronic searches independently in each database. The same investigators then proceeded to identify and remove the duplicate studies. In the next stage, we independently screened the titles and abstracts and obtained all full-text articles marked as “include” or “uncertain”. In the final stage, the same two reviewers independently performed the full text reviews to assess final article eligibility. In case of disagreement, a third reviewer (GN), facilitated a consensus through discussion. The first author (ZL) performed the data analysis. ZL wrote the first draft of the manuscript. All authors reviewed and edited the manuscript and approved the final version of the manuscript.

Acknowledgements: JM was supported by a CIHR Chair in Gender, Work and Health and the Dr. James Roth Research Chair in Musculoskeletal Measurement and Knowledge Translation.

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Table 1 Demographic characteristic of the sample

	Male (N=43)		Female (N=158)
	Mean (SD)	Range, min-max	Mean (SD)	Range, min-max
Age, y	49.2 (12.2)	19 - 74	45.7 (12.8)	19 - 74
Pain intensity	2.0 (1.4)	0 -5	2.1 (1.2)	0 - 5
NDI 10-item	14.6 (10.7)	2 – 44	17.0 (9.8)	0 – 41
NDI 8 item	17.8 (7.0)	0 – 33	19.0 (6.0)	0 – 31.5
NDI 5 item	20.1 (8.3)	0 - 35	21.2 (7.6)	0 - 33
10-item: The total score of NDI 10-item (original) version on ordinal scale with maximum of 50 points. 8-item: The total score of NDI 8-item version on linear scale with maximum of 50 points. 5-item: The total score of NDI 5-item version on linear scale with maximum of 50 points. SD: standard deviation Min: minimum Max: maximum

Table 2 Individual and average agreement of three comparisons

Comparison	Sample size	Degree of freedom	Individual agreement				Average agreement
Comparison	Sample size	Degree of freedom	Mean of difference (d)* (95% CI)	SD of difference	Upper d+1.96SD	Lower d-1.96SD	SE
10-item vs. 8-item	201	200	-2.3 (-4.6 - 0)	5.0	7.4	-12.0	0.4
10-item vs. 5-item	201	200	-4.6 (-9.1 - 0)	5.3	5.8	-14.9	0.5
8-item vs. 5-item	201	200	-2.3 (-4.6 - 0)	2.8	3.3	-7.8	0.2
*p< 0.05 SD: standard deviation SE: standard error base on the mean of difference 10-item: The total score of NDI 10-item (original) version on ordinal scale with maximum of 50 points. 8-item: The total score of NDI 8-item version on linear scale with maximum of 50 points. 5-item: The total score of NDI 5-item version on linear scale with maximum of 50 points. SD: standard deviation SE: standard error

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Editorial decision: Minor revision
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04 Jun, 2020
Review #1 received at journal
20 May, 2020
Reviewer #2 agreed at journal
18 May, 2020
Reviewers invited by journal
15 May, 2020
Reviewer #1 agreed at journal
15 May, 2020
Editor assigned by journal
11 May, 2020
Editor invited by journal
10 May, 2020
Submission checks completed at journal
20 Apr, 2020

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Agreement between Original and Rasch-Approved Neck Disability Index

Status:

Journal Publication

Version 2

Abstract

Figures

Background

Methods

Results

Discussion

Conclusion

Abbreviations

Declarations

Reference List

Tables

Supplementary Files

Status:

Journal Publication

Version 2