This series of articles on the blog "Read It and Weep
"Create a Market Survey for Your Fiction Manuscript"
"What You Should Know About the Amazon Sales Rank"
"Using the Amazon Sales Rank"
"Calculateing Book Sales From amazon's Sales Rank,"
you might find interesting and useful. They address the issue of
inculding a "Comparative Book Survey" and a "Market Survey" with your
fiction submissions and how to prepare these surveys.