# RPI and CTP

## Using Statistics for better Search Engine Optimization

Matthew Henry, Portent Interactive, Seattle, WA
Edited by Ian Lurie
September 22, 2004

A note from Ian: Search Engine Optimization may seem more art than science. And it definitely requires a bit of both. But you can use some basic statistics to focus your campaigns, separate reasonable goals from unreasonable ones, and more efficiently use your search marketing dollars.

Matthew Henry is Portent Interactive’s resident search engine optimization
genius and math wizard. Read on to learn how two of his creations – Relative Position
Index and Click-Through Prediction – help target our SEO campaigns.

## RPI: Your Search Engine Optimization Potential

RPI, or Relative Position Index, is a metric we use to track search
engine optimization potential and progress. Your RPI score shows how
well you’re doing relative to your competitors – it’s an indicator of
how you’re doing at outranking them. It is based on a logarithmic scale,
so an increase of 1 to this value translates into a tenfold increase in
ranking strength.

The formula for RPI is:

RPI = Log10[competition/rank]
competition
is the number of competing sites in a search for this term.
rank
is the rank that your site gets on a search for the term.

In case you’re not a math geek, here’s another way to look at it:

• An RPI of 0 means you rank dead last.
• An RPI of 1 means you rank in the top 10%.
• An RPI of 2 means you rank in the top 1%.
• An RPI of 3 means you rank in the top 0.1%.
• An RPI of 4 means you rank in the top 0.01%.
• An RPI of 5 means you rank in the top 0.001%.

and so on…

Why do we need RPI? Because it’s a good way to judge good search engine optimization targets. For any two keyphrases, doing the same amount of work will get you roughly the same RPI, but the actual ranks may be quite different. So we can use RPI to figure out which terms will get you the highest rank, the fastest, for the same amount of work.

This makes RPI an essential strategic tool – we can figure out
which shorter-term ‘money’ terms will get you a quick burst of traffic,
and plan our longer-term campaign for higher-profile, more competitive terms
that will require more work but also offer a better payoff.

What really makes RPI valuable, though, is that we can look at a web site
and judge the maximum attainable RPI for that site, at that time. It also gives
us goals to shoot for to improve RPI, as well. In my experience, the following RPI
values are realistic goals:

• An RPI of 4 is possible with a medium-sized site with a moderate SEO campaign.
• RPI of 5 is possible for a large site with an aggressive, year-long SEO campaign.
• RPI of 6 is within reach with a huge site with and an aggressive, multiple-year SEO campaign.
• RPI of 7 or 8 is only possible if you happen to run a “Household word” site, like Ebay or Amazon.

Assume a ‘medium-sized’ site has 20-40 pages of quality, text content. A ‘large’
site has 40-100 pages. A ‘huge’ site will have at least 100-200 pages of text content.

So, if we find a set of terms and calculate the RPI necessary to achieve a high rank for
that term, we can use RPI to predict what is or isn’t possible for your search engine optimization
campaign, given your current site. We can also plan out how we might grow your web site, and bring
terms requiring a higher RPI within reach.

## Using RPI to Predict Search Engine Rank

RPI makes it possible to estimate the rank you will achieve for a
given keyword, on a given web site with a given number of pages of text content.

To estimate your potential rank, after search engine optimization, use this
formula:

Rank = competition/10RPI
Round up to the next integer.
competition
is the number of competing sites in a search for this term.
rank is the rank that your site gets on a search for the term.

Important caveat: This is an educated guess only! Your actual rank will be determined by a large number of factors, many of which you have no control over. Your actual rank might be higher or lower than this formula will tell you. The main idea is to make the best guess possible with the information you have.

Here’s an example: Suppose you have a site that can reasonably achieve an RPI of 4 or 5 – it’s a fairly good-sized site, but not over 30-40 pages. Then assume you conduct a moderately aggressive SEO campaign – you optimize your site, add some targeted content and get a few incoming links, so you can achieve a target RPI of 5 for a keyphrase that has 200,000 competing sites. Plugging these numbers into the formula gives you:

200,000 / 105
= 200,000 / 100,000
= 2

The formula predicts a rank of #2.

Note that RPI can be used to make predictions about rank, but it doesn’t tell you anything about the amount of actual traffic you will receive for a term after search engine optimization. For that, you need to use Click-Through Prediction. Read on…

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