Supplementary Material for: Cancer Patients' Preferences for Quantity or Quality of Life: German Translation and Validation of the Quality and Quantity Questionnaire

Background: Decision-making with patients with incurable cancer often requires trade-offs between quality and length of life. The ‘Quality and Quantity Questionnaire' (QQ) is an English-language measure of patients' preference for length or quality of life. The aim of this study was to translate and validate this questionnaire. Materials and Methods: 1 new item was formulated to improve the ‘Quality of life' scale. Construct validity including exploratory factor analysis, convergent and discriminant validity, and reliability was determined in n = 194 patients. Results: The acceptability of the questionnaire among patients was high. The item-non-response rate was very low (2.5-4%). The 2 QQ scales ‘Quality of life' (QL) and ‘Length of life' (LL) had good and acceptable internal consistency (Cronbach's = 0.71 for LL and 0.59 for QL). Convergent validity was shown by significant correlation of the QL subscale with the CCAT (Cancer Communication Assessment Tool) subscale ‘Limitation of treatment' (r = 0.37, p < 0.01) and the LL scale with the CCAT subscale ‘Continuing treatment' (r = 0.24, p = 0.00). Conclusion: The German version of ‘QQ' has satisfactory psychometric properties for measuring patients' preferences for LL or QL. It can be used in all research fields that should be informed by patients' preferences: shared decision-making, palliative care, and health services.