122 Chapter 5 statements, participants were asked to cluster all statements in a maximum of 10 clusters and to name the clusters. No maximum number of statements per cluster was set. Only data from participants who completed both tasks were included in the analysis. For the concept mapping procedure, the computer program Ariadne, version 3.0 was used. This program contains an algorithm which uses the statistical procedure of concept mapping to generate a conceptual framework. The statistical procedure consists of a multi-dimensional scaling procedure and hierarchical cluster analysis.13 This systematic approach and the statistical analyses contributed to the replicability and a high internal validity of the conceptual framework CRE.10,14 Reviews show that concept mapping has been successfully applied to combine these statistical procedures for the analysis of the structure of meaning of statements.15,16 In the first step, the mean rating and standard deviation were calculated for all statements. In the second step, a multi-dimensional scaling procedure resulted in a point map, a two-dimensional map on which all statements are positioned. The distance between the statements on the point map shows to what extent the statements are related. During data collection, this step was repeated until no modifications occurred in the point map. This indicated that the point map was stable and inclusion of participants stopped. In the third step, a hierarchical cluster analysis was performed using the coordinates of the point map. Several cluster maps were reviewed by the research group, resulting in a cluster solution representing the concept of CRE.11 Following the methodology, the last step consisted of a thorough study of the content of the clusters by the research group. This led to minor adjustments of the clusters. Furthermore, the clusters were labelled and described, using the input from the participants from the clustering assignment. Ethical approval The Medical Ethical Committee of the Leiden University Medical Centre has assessed the study protocol for this study and concluded that the Medical Research
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