Psychometric properties of neck disability index - a systematic review and meta-analysis

Purpose To evaluate the data on the psychometric properties of the Neck Disability Index (NDI).Materials and methods Medline, Embase, PsychINFO, Web of Science, and Scopus were searched in April 2023. The random effects meta-analysis was conducted when possible.Results Of 492 identified records, 79 were included. 70 studies were considered to be of low risk of systematic bias. Alpha was >0.81. Pooled test-retest intraclass correlation coefficient was 0.91 (95% CI 0.90-0.93). The NDI correlations with pain rating scales varied from 0.38 to 0.89. 13 studies found the NDI to be unidimensional and 15 - two- or three-dimensional. The minimal detectable change varied from 3% to 27% and minimal clinically important difference from 5% to 33%. Pooled area under the curve was 0.74 (95% CI 0.68-0.80). Most studies have not detected floor or ceiling effect. Sex-related differential item functioning has been present in one study.Conclusions The NDI demonstrated good internal consistency and test-retest reliability without floor or ceiling effect. In most situations, the NDI could be considered a unidimensional scale. The NDI well correlated with the common scales of pain and disability. The minimal clinically important difference and minimal detectable change were around 15% (7.5/50 points).IMPLICATIONS FOR REHABILITATION center dot Based on the 79 observational studies of mostly low risk of systematic bias, the Neck Disability Index demonstrated overall good psychometric properties center dot The Neck Disability Index is a reliable scale to assess the severity of disability caused by neck pain of different musculoskeletal aetiology