The Small Business Guide to Choosing Keywords
In her article for Search Engine Watch, Carrie Hill explains well the use of KEI (Keyword Effectiveness Index) in evaluating keywords. Basically, the KEI compares the frequency with which a keyword phrase is searched for with the number of competing web sites that show up in the results. If the frequency of search is high compared to the level of competition, that results in a high KEI, and indicates a “niche” keyword that may be easier to get great rankings for.
An earlier article in ClickZ also does a good job of explaining KEI, which is always a factor in our own keyword recommendations to clients. She also discusses the two keyword evaluation databases we like: Keyword Discovery andWordtracker.