The KEI is a component within the initial keyword analysis and is an important criteria to consider at the time you’re choosing keywords you want to optimize your site for, and the keyword competitiveness.
The Keyword Effectiveness Index is a ratio of the # Searches per month over the # of Results per month expressed as a percentage. For example: If the # Searches per month were 10,000, and the # of search results is 1,610,000, then the KEI is 0.62%.
The higher the KEI, the more popular your keywords are, AND the less competition they have. That’s a good indication that they are gonna be easier, quicker, and less expensive to optimize than a lower KEI.
However, the KEI can be deceiving. Imagine if there are a low amount of competitors…but they had very strong inbound link profiles, and were optimized to the hilt? You’d might think by only looking at the KEI that you’d be able to perform well on this keyword, but think again. Once you’ve identified your keyword to optimize for, you’ll need to examine at least the top 10 competitors in the SERPs. And, in some cases you’ll see the first 3 pages in the SERPs dominated by very strong authoritative and SEO’ed websites.