Congruent with these, 216 (23 × 33) scenarios were developed to describe hypothetical patients. However, according to the literature plausible scenarios should not exceed 30 [6, 34]. To reduce the number of scenarios, the authors used the SPSS 21.0 procedure  to develop a fractional factorial design and reduce the 216 possible scenarios to 16. Winkelhage and Diederich  used the same methodology in their research to a sample of German citizens. This model ensures that after the data analysis, the importance of each particular attribute (characteristics) and each level assigned to it will prevail, while all other attributes will remain constant.