I include MDS analysis in a customer survey and have about 10 brands I want to include in the perceptual map at the end. Meaning the customers would have to rate 45 comparisons and give a similarity rating of 1 to 7 to each of the 45 comparisons.
Now my question. Is it a problem when NOT all customer rate the similarity of all comparisons? Meaning, I would have missing values for certain similarities between two brands. Especially for the case when I aggregate the individual answers to create an aggregate solution.
I plan to do the analysis with R and don't know exactly how I can handle missing values in a MDS analysis and if they will have an impact on the explanatory power at the end.