I know this is a late response, but I figured I'd toss my two-cents in here.
KEI (Keyword Effectiveness Index) is a formula for determining the popularity of a keyword (i.e., how often it is searched for and how often your competitors are using it). The Wordtracker online software actually calculates something like this for you (which I find extremely helpful).
Also for "keyword misspellings" do a G search for keyword misspellings :)
in relation to KEI, (Keyword Effectiveness Index ... this measure has long been ineffective and in my opinion should not be used. There are far more effective ways to measure the effectiveness of a keyword, such as in title, in anchor, saturation etc...