In order to allow accurate estimation of the preference associated with each item, the MDS statistical design must be properly prepared and must satisfy some balance criteria.
- one-way balance: items are included in the design a similar amount of times;
- two-way balance: each combination of items appear together (on the same task) in the design a similar amount of times;
- positional balance: each item appears in each position (first, second, third, etc) a similar amount of times;
- within-version balance: items appear within each version (block) a similar amount of times.
The function generate.design.MDS available in R-sw Tradeoff generates a MDS design. It is possible to specify prohibitions, i.e., combination of statements that should not appear in the design. In addition, the function automatically provides a report with the design properties, i.e., how it is performing on the various balance criteria.
The function check.design.MDS produces summary statistics for an existing MDS design.