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KE Why? Is the Keyphrase Effectiveness Index worth your time?

10 Dec 2009 by Graham Lyons - SEO , No Comments


There’s a lot of talk in search engine optimisation circles about whether or not the Keyphrase Effectiveness Index (or KEI) is a useful measure to take into account when you are selecting keyphrases to optimise for.  In this post I’m going to look at exactly what the KEI is, how it is calculated and discuss whether it is a worthwhile metric to calculate when analysing a keyphrase.

What is the KEI?

KEI stands for Keyphrase Effectiveness Index and is a value given to a keyphrase which attempts to balance how popular (traffic-wise) a keyphrase is with the amount of competition that a new website optimising for the keyphrase will face.

When creating the formula to calculate the KEI there were 3 main relationship changes that need to be satisfied:

  • Popularity/traffic increases:  When the popularity of a keyphrase (which is based on the quantity of traffic that it generates) increases then the KEI should also increase.
  • Competition Increases:  When the quantity of websites that are optimising for the keyphrase increases then the KEI should decrease to represent the increase in difficulty.
  • Popularity and Competition increase in tandem:  When popularity and competition both increase (but the ratio between the two is maintained) then the KEI should increase.  The reason for this is that, although the ratio between the 2 values stays the same, the increase in traffic makes the keyphrase more attractive.

How Is KEI calculated?

There is no single formula that has been established as THE way to calculate KEI, instead it is accepted that any formula which satisfies the above 3 conditions is acceptable.  The most commonly used formula however is KEI = (popularity (P) ^2)/Competition(C) although the power that you choose for P can be adjusted (for example KEI = (P^3/C) and KEI = (P^2.5/C) are equally valid).

In this formula P (popularity) is typically calculated by using the average monthly searches for the keyphrase.  This figure can be discovered by using a keyphrase analysis tool; such as the free Keywords Tool from Google AdWords.

C (competition) is usually based on the number of results that Google provides when you conduct a search for the keyphrase.

For example if I was optimising for the keyphrase “jean paul gaultier aftershave” Keyword Tool tells me that I can expect traffic of 1900 and a Google search shows me 285000 results.  These figures will be used as P and C respectively meaning that the KEI = (1900^2)/285000 = 12.66.

Why Use KEI?

The reason that people use KEI is that it provides a quick and simple way to compare keyphrases on a consistent basis.  Some keyphrase analysis tools (such as wordtracker) even automatically calculate the KEI making comparison of keyphrases based on the metric an extremely fast and straightforward process.

Should Keyphrase Selection Be Based on KEI?

We would all love it if there was a simple formula that could be applied to every keyphrase and provide us with an accurate answer as to whether the phrase is worth optimising for; unfortunately KEI (like many similar formulae that are devised with the idea of making a relatively arduous task a simple and straightforward one) over simplifies the process of selecting keyphrases.

The biggest flaw in the KEI formula is that it completely fails to take into account the strength of the competing websites.  When it comes down to it, using the number of webpages that are listed in Google for a keyphrase as the competition can prove hugely inaccurate.  In reality it is the strength of the competition that will really impact the difficulty of optimising for a keyphrase.  For example you might want to optimise for a product that falls into a particular niche.  It is possible that due to the narrow appeal of the phrase there are relatively few websites already ranking for this phrase.  However the top ten sites might already be large, well established sites with high page ranks and devoted visitors.  In this instance the KEI will be high (due to the low number of competing pages) but in reality it will be extremely tough to take over the established sites.  Conversely the opposite can be true on occasion; when huge numbers of websites rank for a particular page but no one strong site specialises in it, thus leaving the door open for a new site to enter.

This is not to discount KEI altogether, as a part of the keyphrase selection process calculating the KEI can be a worthwhile endeavour: it does provide a quick and easy way to compare phrases like for like.  However it is vital that you also investigate other factors (most notably the strength of the competition) before settling on a final set of keyphrases.



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