Cross-cultural validation of the WHO disability assessment schedule 2.0 for people affected by neglected tropical diseases in Niassa Province, Mozambique.
Background: Neglected tropical diseases (NTDs) are a diverse group of infectious diseases that may cause chronic, disabling and often disfiguring conditions. NTDs disproportionally affect the most marginalized people an people living in low-income countries. Annually, up to 1,000,000 people die due to the consequences of NTDs, of which Sub-Saharan Africa bears the biggest burden. However, the burden of NTDs is even bigger when the disabilities they cause are taken into account; globally, NTDs are accountable for at least 57 million disability-adjusted life-years. Moreover, several studies have stated that the actual burden of NTDs is generally underestimated and that the economic, social and psychological impact combined, is larger than has ever been estimated before. This underestimation is caused by the lack of accurate data on NTDs and the disabilities they cause. This lack of data, in turn, is the result of the disagreement among NTD experts about appropriate measurement instruments to assess and monitor the morbidity and disability aspects of NTDs. To address this gap, Van 't Noordende et al. developed a toolkit for the assessment of NTDs' morbidity and disability: the neglected tropical diseases, morbidity and disability toolkit (NMD-toolkit). Based on a literature review and a Deplhi study the most relevant instruments, regarding morbidity and disability, were selected for the NMD-toolkit. In order to use the NMD-toolkit worldwide, the questionnaires included in the toolkit need to be validated across cultures and NTDs, as it cannot be assumed that a questionnaire is equally suitable across cultures and diseases. Therefore, this study examined the cross-cultural equivalence of one of the included questionnaires; the World Health Organisation disability assessment schedule 2.0 (WHODAS 2.0). For this validation study the cultural equivalence framework developed by Herdman et al. and adapted by Stevelink et al. was used. Semantic, conceptual, item, operational, measurement and cultural equivalence were assessed. Research question: To what extent is the WHODAS 2.0 a culturally valid instrument for people affected by NTDs in Niassa province, Mozambique? Methodology: For this study a sequential exploratory mixed-methods design was used. The study took place in Niassa province, Mozambique and included patients affected by leprosy, trachoma, lymphatic filariasis (LF) or a combination of these. First, the WHODAS 2.0 was translated into the local language Macua, according to the WHO guidelines 'Process of translation and adaptation of instruments'. Then, semantic, conceptual, item and operational equivalence were assessed in a pilot study by means of eight qualitative interviews. These data were used to adapt the WHODAS 2.0 to the local setting. Lastly, 130 patients were interviewed to assess the measurement equivalence of the adapted and translated WHODAS 2.0. To assess reproducibility twenty patients were interviewed again after twelve days. Cronbach's α were calculated to assess internal consistency. Construct validity was assessed by testing the correlation between the WHODAS 2.0 total scores and participation restriction (measured by using the Participation scale) and disability severity scores (measured by the Eye Hand Foot score for leprosy and separate grading scales for trachoma and LF).Reproducibility was examined by measuring agreement and reliability. Agreement was assessed by measuring the standard error of measurement (SEM) and multiplying the SEM by 1.96 and the square root of 2 to calculate the smallest detectable change (SDC). The Intra-class correlation coefficient agreement (ICC agreement) was calculated to assess reliability. Lastly, the presence of floor or ceiling effects were examined. Results: The WHODAS 2.0 was successfully translated to Macua. In the pilot study most participants indicated that they understood all questions and that the questions were important, relevant and appropriate. Participants were unable to answer questions relating to the WHODAS 2.0's conceptual equivalence. Furthermore, several problems regarding the WHODAS 2.0's format were encountered. For measurement equivalence the Cronbach's α values ranged from 0.32 to 0.57 for various sub groups. WHODAS 2.0 total scores were not associated with participation restriction nor with disability severity scores. The SEM was 4.33, the SDC 12.0 and ICC agreement was 0.19. Lastly, no floor and ceiling effects were observed. Conclusion: The findings showed that the WHODAS 2.0 has good semantic and item equivalence, questionable conceptual equivalence and inadequate operational equivalence in Niassa province, Mozambique. The only positive results found for measurement equivalence, was the absence of floor and ceiling effects, thus measurement equivalence is also considered inadequate. Therefore, the WHODAS 2.0's cultural equivalence is questionable. Further validation studies need to determine whether the suggested adaptations in this study will make the WHODAS 2.0 a valid and reliable instrument for people affected by NTDs in Niassa province, Mozambique. For further use of the NMD-toolkit, inclusion of a new scale for the activity domain is suggested.