*2.3. VAS Matrix for the Criteria Weighting*

VAS matrix can be used as the data collection tool in the survey-based decision. For instance, VAS scales are implemented in the SEIQoL methodology, which is widely used to nominate, weight, and rate different aspects of life quality [49]. SEIQoL with a direct weighting technique (SEIQoL-DW) is an interview-based tool that involves the interviewer to manage the evaluation process. The respondents are asked to nominate the five most important areas of their life (domains) in these semistructured interviews. For the evaluation of the importance of these domains, point allocation weighting is applied. Vertical VAS matrix with five adjacent VAS scales is used to assess the current functioning in the chosen domains. Finally, five separate indexes are calculated summing up the products of the functioning level and the relative weights.

Such a methodology is widely applied in various studies [50]. However, experiments with the SEIQoL-DW revealed that looking at the VAS matrix respondents comprehends the task as the assessment of the domain importance rather than the scoring of their functioning at the research moment [49].

Burckhardt et al. [46] proposed to employ VAS scales and the direct weighting for both the scoring and the weighting of the chosen domains. He also excluded the interviewer from the experiment and used a self-explanatory paper questionnaire to collect the data. In total, 100 participants were involved in this research. Since the averaged values of the VAS based DR technique showed a tendency toward the low variability of the domain weights, the usefulness of the improved methodology was highly questioned. Nevertheless, it must be noted that neither the subjectivity of the respondents nor the psychometric features of the VAS scales were analyzed in the domain importance assessments. We strongly believe that these aspects should be cautiously analyzed when the survey-based criteria weighting is performed.
