Gm, thank you so much for running that analysis. Even after researching, I'm still not clear on how to interpret the test outputs (u value, etc), but your note that "there is no significant difference in # of orders between the 2 categories in each set" makes sense.
Regarding the details of my data, it's really simple. Using "Set 1" as an example, I called a bunch of companies and asked them who they prefer to refer their employees to for medical care and then I recorded their answers. If they said they prefer to refer their employees only to the company named Brook, then I categorized them as a "Brook only" company. If they said anything else, then I categorized them as "not Brook only". I then looked up the last 6 months of Brook's sales data to employees working at each company to see if they actually purchased product from Brook. I'm trying to determine if it matters to Brook's sales whether or not these companies say they prefer to refer their employees only to Brook, or if they say anything other than that. Brook works really hard (and spends a lot of money) to get these companies to tell their employees to go to Brook for medical care and I'm trying to determine how much those efforts matter, if at all. If Brook can expect to produce the same amount of revenue to employees working at "not Brook only" companies as it can to "Brook only" companies, then there is an opportunity to make big changes and re-allocate significant $'s.
I hope that makes better sense. If that explanation gives you a better idea of my situation and what I'm trying to accomplish, then do you still think the Mann-Whitney Test is most appropriate?
Thanks again! I'm really grateful for the assistance.
