Revision and validation of the German version of the Systemic Sclerosis Quality of Life Questionnaire (SScQoL) with Mokken scale analysis

Kocher, A.; Ndosi, M.; Hoeper, K.; Simon, M.; Nicca, D.

Abstract

In the validation study, German-speaking SSc patients included in the Swiss MANagement Of Systemic Sclerosis (MANOSS) cross-sectional study completed the revised (polytomous) SScQoL. Mokken model was used to test the construct validity of the scale including its subscales. The scalability (H coefficient) values of . 0.50 are considered gstrongh, 0.49 to 0.40 gmoderateh and 0.39 to 0.30 “weak” scales, while values of < 0.30 are not considered as unidimensional. Internal consistency (reliability) was assessed using Cronbach's α. The validation sample comprised 79 patients (74.7% female) with a median age of 61 (IQR: 49 to 71) and disease duration of 8 (IQR: 4 to 13) years. Table 1 presents the results of validation with Mokken model. The construct validity of the revised German SScQoL was confirmed in all subscales and the global scale. The scalability (H, coefficients) were all above 0.50 suggesting a robust unidimensional scale. Internal consistency was high (Cronbach's α = 0.97). Background: The Systemic Sclerosis Quality of Life Questionnaire (SScQoL) has been validated in six European languages.1 Previous adaptation into German revealed issues with the dichotomous response structure in 10 items necessitating a review of the tool and further psychometric testing with patients in German speaking countries. Objectives: The aim of this study was to assess the German version of the SScQoL, extend the response structure and test its construct validity using Mokken scale analysis. Methods: This was a mixed methods study involving cognitive debriefing and survey methods. The expert committee extended the response structure of the 10 items from dichotomous to polytomous (4-point) responses: ‘always’, ‘usually’, ‘sometimes’ and ‘never’. In cognitive debriefing, a small convenience sample of patients with SSc completed the new version while ‘thinking aloud’ and commented on relevance of the items and the response structure. Results: In cognitive debriefing, six patients with SSc completed the new German SScQoL and reported problems with the remaining dichotomous items. These were subsequently converted into polytomous 4-point response structure by the expert committee. Conclusion: The German SScQoL has been revised into polytomous item structure and shown to be a valid and reliable measure of health-related quality of life in SSc. Further cross-cultural validity tests are required to assess its measurement equivalence with other SScQoL versions and thus enable multinational comparisons. References: [1]Ndosi M, Alcacer-Pitarch B, Allanore Y et al. Common measure of quality of life for people with systemic sclerosis across seven European countries: a cross-sectional study. Ann Rheum Dis, 2018; 77: 1032-1038 Disclosure of Interests: Agnes Kocher Grant/research support from: Sandoz to support the development of an eLearning module for patients with rheumatic diseases., Mwidimi Ndosi Grant/research support from: Bristol Myers Squibb, Consultant of: Janssen, Pfizer, Kirsten Hoeper Consultant of: AbbVie, Celgene, Speakers bureau: Abbvie, Chugai, Novartis, Lilly, Celgene, Sandoz Hexal, Michael Simon: None declared, Dunja Nicca: None declared Table 1 Mokken scale analysis of the revised German SScQoL Subscale (items) Scalability (H) Standard error Function (6) 0.664 0.048 Emotional (13) 0.652 0.060 Sleep (2) 0.798 0.061 Social (6) 0.692 0.053 Pain (2) 0.960 0.029 Global scale (29) 0.623 0.062 Table legend: scalability H ≥ 0.50 = strong, 0.49 to 0.40 = moderate, 0.39 to 0.30 = weak, while values of < 0.30 are not considered as unidimensional.

• Presentation Conference Type: Conference Abstract
• Conference Name: EULAR European Congress of Rheumatology
• Start Date: Jun 3, 2020
• End Date: Jun 6, 2020
• Acceptance Date: Apr 1, 2020
• Online Publication Date: Jun 2, 2020
• Publication Date: 2020-06
• Deposit Date: May 29, 2021
• Journal: BMJ
• Print ISSN: 0003-4967
• Electronic ISSN: 1468-2060
• Publisher: BMJ Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 79
• Issue: S1
• Pages: 554-555
• DOI: https://doi.org/10.1136/annrheumdis-2020-eular.1156
• Public URL: https://uwe-repository.worktribe.com/output/6013007
• Publisher URL: https://ard.bmj.com/content/79/Suppl_1/554.1