Validity and test re-test reliability of the neck disability index in the Nigerian clinical setting

The neck disability index (NDI) is a valid and widely used clinical instrument, which enjoys the recommendation of the World Health Organization for outcome assessment in neck pain. Its psychometric properties have not been investigated in the Nigerian clinical setting. This study investigated the content validity and test-retest reliability of the NDI in order to encourage its integration in the Nigerian clinical setting. Content validity of NDI was assessed through an expert panel review for content relevance/coverage and pretesting. Thirty two subjects with neck pain, recruited through a purposive sampling technique participated in the study. The NDI was administered twice within 48 hours interval. Data were summarized in percentages. Intra class correlation coefficient was used to analyze data for test-retest reliability with alpha set at 0.05. Participants were 1 males, 21 females with a majority within age group 38-57. Twenty four (75%) participants had mild to moderate disability, 7 (21.9%) had severe to complete disability and one individual had no disability. There was a significant correlation (r = 0.969, P=0.01) between the scores obtained from the first administration of the NDI and the second administration. The NDI is a valid and reliable outcome measure and it is recommended for integration into the assessment of neck pain in the Nigerian clinical setting.