Klaske van Sluis

96 6.2. Materials and methods 6.2.3 Grouping of respondents For the analysis of the primary and secondary outcomes, the respondents were grouped. The grouping was based on: • Sex: male vs. female • Age: <60 years of age vs. 60+ years of age. In the questionnaire, the respondents were asked to indicate their age through a choice between five decade age brackets. The age brackets were simplified in our analyses to just two age groups, roughly representing the ‘pre-retirement’ age group and ‘post-retirement’ age group. • Time since TL: < 2 years since TL vs. 2+ years since TL. This grouping was based on clinical experts consensus that the most initial rehabilitation issues of the TL procedure are resolved within two years. • Educational level: respondents without tertiary education (defined as an educational degree after High School) vs. respondents with tertiary edu- cation. • Country of residence: country specific analyses were only performed for countries with a response rate of > 5%. The countries Sweden, Brazil and Spain were therefore excluded in this specific analysis. 6.2.4 Grouping of questions Because this questionnaire was not based on validated QoL scales or validated questionnaires, we performed a clustering of semantically related questions into general issue themes. Because some questions could belong to multiple themes, the semantic clustering of questions was based on the experience of the clinical experts (K. E. v S. and M. vd B.), discussed in multiple consensus meetings. The self-reported ratings of overall health and independence (both rating scales from 0 to 10) were combined to one sum measure: the reported r-QoL rating (scale from 0 to 20). In this article, the term r-QoL is used to refer to this combined measure of the following two specific scale questions: • “How would you rate your overall health from 0 to 10? 0 means worst imaginable health state, 10 means best imaginable health state” • “On a scale from 0 to 10, how independent do you feel in completing the activities you want? 0 means the least imaginable independence in completing the activities you want, 10 means the most imaginable inde- pendence in completing the activities you want” The internal correlation between these two scale questions is textitR 2 =.366 (percentage of variance explained).