Agreement between original and Rasch-approved neck disability index

Ze Lu,Joy C Macdermid,Goris Nazari

doi:10.1186/s12874-020-01069-w

Abstract

BackgroundGiven the high prevalence of neck pain, the neck disability index (NDI) has been used to evaluate patient status and treatment outcomes. Modified versions were proposed as solutions to measurement deficits in the NDI. However, the original 10-item NDI was scored out of 50 and is still the most frequently administered version. 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.MethodsThe current study was a secondary data analysis. The study data was compiled from two prospectively collected data sources. We performed a comprehensive literature search to identify Rasch approved NDI within four databases including Embase, Medline, PubMed, and Google Scholar. Alternate forms and scorings were compared to each other and to the standard NDI. We graphed B&A plots and calculated the mean difference and the 95% limits of agreement (LoA; ±1.96 times the standard deviation).ResultsTwo Rasch approved alternative versions (8 vs 5 items) 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).ConclusionTwo Rasch-based NDI solutions (8 vs 5 items) which differ in number of items and conceptual construction are available to provide interval level scoring. They both provide scores that are substantially different from the 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.

Highlights

Given the high prevalence of neck pain, the neck disability index (NDI) has been used to evaluate patient status and treatment outcomes
The The 10-item version of neck disability index (NDI-10) is the most studied neck-related patient-reported outcome measure (PROM) as it has been cited and applied in more than 300 publications [21]. It has been used widely in surgical treatment, injection therapies, physical therapy, as well as within exercise and research context [15, 16, 21]. Both a systematic review [16] and an overview [3] have reviewed a large volume of psychometric evidence on NDI with most studies suggesting that the NDI-10 has excellent classical psychometric properties, while a few studies have raised concerns about its factor structure, item relevance or scaling
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)

Summary

Introduction

Given the high prevalence of neck pain, the neck disability index (NDI) has been used to evaluate patient status and treatment outcomes. The first patient-reported outcome measure (PROM) that assessed pain and disability in participants with neck pain was published in 1991 – the 10item version of neck disability index (NDI-10 )[22]. The NDI-10 is the most studied neck-related PROM as it has been cited and applied in more than 300 publications [21]. It has been used widely in surgical treatment, injection therapies, physical therapy, as well as within exercise and research context [15, 16, 21]. The original version of the NDI-10 has been translated into 22 languages versions [9, 21]

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