I have three main areas of my site and want to track total usage as well as breakdowns of the three parts. I am trying to segment the "type" of use on each page using a custom variable as such:

['_setCustomVar',1,'Visitor Type','Unknown',1]

Visitor type can be one of three values: "Unknown", "Reader" or "publisher".

Every page has this value set. Now when I look at my analytics chart and chose all three segments, the individual values do not match the sum. I've double checked the pages to make sure the custom var is there.