What is the Best Keyword Difficulty Metric?

Keyword research is arguably the most important step in the SEO process. It’s the perfect antidote to Google’s recent algorithm updates making it increasingly expensive, complicated, and risky to attempt to “punch above your weight” by manipulating your way to the top of the search engine results: just find keywords where your site is already competitive. Or at least, where the competition is weak enough that ranking won’t take every trick in the SEO book.

As one of the the fundamental principles underlying CanIRank is that less SEO is better SEO, one of our goals was to create the single best measure of keyword difficulty, so that users can tell at a glance whether or not their site is competitive for a given keyword.  The result is the CanIRank Ranking Probability score, the first measure of keyword difficulty that assess keyword difficulty relative to your website.

keyword difficulty score

CanIRank’s Ranking Probability is more actionable than traditional Keyword Difficulty scores.

Other tools will tell you that “home loan” and “SEO” both have about the same keyword difficulty (85-87%). CanIRank will tell you that QuickenLoans.com scores a 100% Ranking Probability for “home loan” but only 77% for “SEO”, while SEOBook.com has a 95% Ranking Probability for “SEO”, but only a 72% chance of competing for “home loan”. As a site owner, getting keyword difficulty scores relative to your website is both more accurate and more actionable.

Not only are accurate Ranking Probability predictions important for helping to guide you in making the right decisions, but they’re also a reflection of our understanding of search engine ranking factors. When CanIRank makes accurate predictions, it suggests our ranking models do a good job capturing the impact of various ranking factors. This understanding of ranking factors is what enables us to then draw meaningful comparisons between websites, highlight areas in need of improvement, and recommend Actions that will have the greatest impact on your site’s ranking.

So we’ve invested a lot of time, money, and research into creating what we feel are the most sophisticated ranking models in the SEO universe.

accuracy of seo metrics

How well do they work?

The short answer is that while no predictions are perfect (just ask the weather man), CanIRank is over twice as accurate as other SEO tools, and can be used to explain a majority (but not all) of the ranking differences between websites.

More specifically, as a measure of how competitive a given web page will be in the Google search results, CanIRank’s Ranking Probability score is:

Before I dive into the analysis, I’d like to emphasize that all of the above are excellent and useful SEO tools, and this post is in no way an attempt to disparage or put down competing offerings. While CanIRank comes away looking pretty good in this study, it’s far from an exhaustive analysis, and all of the tools have their own strengths and weaknesses which I hope you’ll explore to determine what best meets your needs.

The Experiment

I based this experiment on the notion that an ideal metric for a page’s competitiveness would have a perfect rank order correlation to Google search results. That is, for any given keyword the #1 result in Google should always have a higher competitiveness score than the #2 result, which should have a higher score than the #3 result, and so on. Perfectly ranking 40 search results in the correct order would require that a metric encapsulates many of the same factors that Google considers, and also weights them similarly. In other words, it’s quite a rigorous standard for a competitive analysis tool, especially as for practical purposes it’s not as important that we can correctly order a #3 result before a #4 result as it is that we can tell when a URL is likely to rank #4 and when it is likely to be #40 (or not ranking at all).

russian dolls in order

Can SEO metrics order results correctly?

To measure how closely popular SEO metrics come to this ideal, I first pulled the top 40 Google results for 25 keywords randomly selected from a batch of 2 million keywords used in PPC advertisements. For each of the resulting 1,000 URLs, I collected the CanIRank Ranking Probability score, SEOMoz Page Authority, Google PageRank, MajesticSEO CitationFlow, and SerpIQ Competition Index. I then threw out all the URLs where SEOMoz didn’t have any data, leaving just under 700 results.

For each keyword, I then ranked the URLs according to each metric, and calculated the correlation between the rankings predicted by the metric, and the actual ranking in the Google results. Statistics geeks will recognize this as Spearman’s Rank Order correlation coefficient. A coefficient of 1 suggests the rank order of the two variables is perfectly correlated, while a coefficient of 0 means that there is no correlation.

Here’s an example of what the keyword table looks like for one of the keywords, “bankruptcy NJ” :

table of google results ranked by seo metrics

You may recognize this methodology as similar to past studies conducted by SEOMoz to determine the correlation between various web page attributes and high Google rankings, in which they’ve uncovered correlations ranging from 0 for keywords in an H1 tag to 0.03 for content length to 0.25 for # of linking root domains (the highest correlation).  You may be relieved to discover that, in this data sample at least, all of the SEO metrics outperformed nearly all of the raw page attributes. Woo-hoo! Perhaps there’s something to this SEO stuff after all.

The Results

correlation with Google search results

In order from lowest mean correlation to highest, let’s examine the suitability of each individual metric in more detail. Please keep in mind that this is an apples to oranges comparison as each of these metrics is designed to capture something slightly different, and as far as I know only CanIRank is even attempting to capture all of the factors that go into determining a URL’s competitiveness.

SerpIQ – Competition Index – 0.17

serpiq-logoSerpIQ’s Competition Index is “designed to give you a quick snapshot of the average difficulty of a Search Engine Rankings Page (SERP). The score is calculated by looking at the main ranking factors for a site, mainly: domain age, page speed, social factors, on page seo, backlink amount and quality, and PageRank.” Unfortunately I wasn’t able to get a Competition Index score for URLs beyond the top 10 results for each keyword, so SerpIQ’s correlation of 0.17 was calculated based upon the top 10 results only.

MajesticSEO – CitationFlow – 0.19

majestic_largeCitationFlow is Majestic’s version of Google PageRank, described as “a number predicting how influential a URL might be based on how many sites link to it.” As with PageRank, CitationFlow gives more weight to links from pages that themselves have many inbound links. As a predictor of Google rankings, CitationFlow was about as useful as PageRank, with a mean correlation of 0.19.

Google – PageRank – 0.21

logo4wGoogle’s PageRank, measured on a 0 to 10 scale and intended to capture the relative importance of a web page, was once the only game in town as far as metrics go. Unfortunately it’s become much less reliable in recent years, and most SEOs don’t put much weight in it anymore. However, as a predictor of Google rankings, PageRank scored the third-highest correlation, suggesting that it does indeed still seem to play a role. I used RankSmart’s handy bulk PageRank checker to collect the data for this study.

Moz – Page Authority – 0.27

Moz-logoMoz (previously known as SEOMoz) describes their Page Authority metric as “Moz’s calculated metric for how well a given webpage is likely to rank in Google.com’s search results”. There are some pretty smart folks up in Seattle working for Moz, and it shows in the excellent performance of their Page Authority metric, which had the second-highest correlation with Google search results. This is especially impressive, considering that (as far as I know, at least) Page Authority is not intended to capture any relevancy factors. In their own studies, Moz has calculated Page Authority correlations as high as 0.38; I’m not sure why the result is so much lower in my study.

CanIRank – Ranking Probability – 0.57

logoCanIRank’s Ranking Probability scores had the highest correlation to Google search results, with a mean rank order correlation coefficient of 0.57. Of course, this is to be expected as Ranking Probability is really the only measure intended to capture the complete picture of search engine ranking factors. Although 0.57 represents a fairly strong relationship between the variables (by comparison the correlation between IQ and academic grades is around 0.5), I think we can still do much better, and there are a number of improvements in the works which I think will push this number even higher.


With a rank order correlation coefficient of 0.57, CanIRank’s accuracy is high enough for us to feel comfortable claiming that Ranking Probability scores can be useful in assessing whether or not a web page is competitive for a given keyword. Of course no one outside of Google knows what factors are included in their algorithm, and they have access to all kinds of data (such as Chrome, Google analytics, Android, SERP click-tracking, etc) that other companies do not have. Our goal is not to replicate their algorithm, but simply to find out whether a ranking model built upon publicly available information retrieval concepts would correlate strongly enough to draw useful conclusions. We think this study demonstrates that this is possible, and with further work we hope CanIRank will be able to provide even more useful guidance.


How Much is a #1 Ranking Worth to Your Business?

Estimating the Traffic Value of a potential target keyword is a critical step in a comprehensive keyword research process. If you know how much value a top ranking will bring to your business, you can better determine how much time and money it would be worth investing in SEO. You can even calculate the ROI of each keyword you’re considering, and choose to target keywords that will bring the most additional revenue for the least cost. That’s the kind of accountable marketing that even your CFO will love!

The Traffic Value of a keyword is a function of a) the value to your business of a visitor who searched for that keyword (Earnings Per Click), and b) the number of clicks you receive from that keyword (# Clicks). Here’s a simple formula:

Traffic Value = Earnings Per Click * Num Clicks


In SEO the number of clicks is determined by the total number of people searching for that keyword (# Searches) times the percentage of people who click on your search engine listing (Click-Through Rate), so the formula becomes:

Traffic Value = Earnings Per Click * Num Searches * CTR

Calculating the Traffic Value of a Keyword – Example

As an example, let’s assume that 500 people per month search for the keyword “Yoga DVD reviews”. The owners of YogaDVDs.net have calculated that each visitor to their website looking for “Yoga DVD reviews” is worth $0.50 (more on how they determined this below).  On average 40% of searchers click on the #1 ranking. The Traffic Value of “Yoga DVD reviews” can be calculated as:

Traffic Value = $0.50 * 500 * 40% = $100/ month

$1200 a year may not sound like a lot, but in practice the improvements you make to gain a #1 ranking for a competitive keyword like “Yoga DVD reviews” inherently results in top rankings for lots of other less competitive related keywords, like “best Yoga DVDs”, or “Yoga DVD ratings”. I call these “Satellite Rankings” because they are effortlessly pulled in by the “gravity” of the much larger keyword. In my experience Satellite Rankings can easily lead to a doubling or tripling of the Traffic Value of a keyword.  In some cases the combined value of primary + Satellite Rankings ends up being 10 times the value of the primary keyword alone!

Let’s look in more detail at how to estimate each component of the Traffic Value formula:

Earnings Per Click

There are two ways to estimate your Earnings Per Click: the Best Way, and the Easy Way. The “Best Way” is to calculate your Earnings Per Click based upon your own sales statistics. For example, if you had 1,000 visitors from the keyword “Yoga DVD reviews”, 5% of those customers went on to make a purchase, and your average profit per new customer is $10, you earned $500 on those 1,000 clicks, so your Earnings Per Click is $0.50.

Earnings = 1,000 visitors * 5% conversion * $10 profit = $500
Earnings Per Click = $500 / 1,000 clicks = $0.50

But how are you supposed to know those numbers if you’re not yet ranking for the keyword? Well, there are a couple of options. First, you can buy some advertisements on the keyword through a pay-per-click ad program like Google AdWords. Track how many clicks you receive from that keyword and how many sales those visitors make, and you can easily calculate your Earnings Per Click. Another option is to estimate your Earnings Per Click based upon the performance of a similar keyword.

If the above sounds like too much work, the “Easy Way” to calculate your Earnings Per Click is to base it upon the average Cost Per Click for that keyword on Google AdWords. The basis for this is that many advertisers are willing to bid right up to the value of a click, so in essence you are piggybacking on the work the advertisers have already done calculating their respective Earnings Per Click. To get the Google AdWords Earnings Per Click, search your keyword on Google’s Keyword Planner (a free Google AdWords account is required to use the Keyword Planner).

Cost Per Click from Google Keyword Planner

The Google AdWords Keyword Planner tool provides estimates for monthly search volume and average Cost Per Click.


Number of Searches

Google’s Keyword Planner is also your best source for data on the number of searches a keyword receives. Unfortunately, the numbers that Google provides can be somewhat unreliable, so if you’re interested in a more precise estimate the best method again is to take out an ad on the keyword via Google AdWords (keep in mind that the organic search listings receive 5 times as many clicks as the paid ads!).

Click-Through Rate

The Click-Through Rate (CTR) on your search listing will depend upon your ranking in the search results, and the attractiveness of your listing relative to the other results. It should come as no surprise that the top rankings receive the majority of clicks. Studies have shown that the #1 ranking receives from 50-60% of the clicks, #2 is clicked about 12-15% of the time, #3 about 9% of the time, and the remaining results go down from there. Only 1 in 10 searchers click on a listing beyond the first page.

distribution of clicks on search results

Most of the clicks go to the top few rankings.

While these figures are for the average search result, sometimes there are factors which cause CTRs to deviate from the norm. For example, brand searches like “Puma shoes” or navigational searches like “IRS Form 1040″ are likely to have nearly all the clicks concentrated on a single result (the Puma home page and the official IRS page for the 1040 form, in these cases). Well-known brands generally attract a lot of clicks regardless of where they’re ranked. For example, people searching for “HDTV reviews” are more likely to click on a listing for CNET or Consumer Reports even if they’re ranked #3 or #4, if the #1 result is an unknown brand like Brads-hdtv-reviews.biz.

To estimate your CTR, consider how attractive your result snippet is relative to the existing results. If there are much bigger companies than yours included and they do a good job addressing the needs of the searcher, count on receiving less than 50-60% of the total search volume even if you do reach the #1 position.

Maximizing the ROI of your Content Marketing

Now that you know how to calculate the Traffic Value of a keyword, your SEO and Content Marketing efforts can be optimized just like any other marketing channel: generate maximum sales with minimal spend. So how do you calculate the cost of ranking for a keyword? That’s where CanIRank’s Ranking Probability scores come in. Higher Ranking Probability scores equate to a lower Ranking Cost. In general, a Ranking Probability score of 90% or above means that your costs will be limited to content production and following your usual content promotion process. A Ranking Probability score around 80% means you’ll also need to dedicate a few hours a week to completing SEO tasks for a month or two. Scores around 70% or lower usually mean that you’re looking at several months work of regular SEO work, or spending heavily on more aggressive promotion.

With a little practice you’ll start to figure out what cost a given Ranking Probability score equates to for your particular website. Then it’s simply a matter of comparing each keyword’s Ranking Cost with its Traffic Value and you are on your way to making much better decisions in your content marketing.

How to Get the Most from CanIRank

Used correctly, CanIRank isn’t just a way to help you find new keywords to target; it’s an entirely new approach to growing search engine traffic that will help you dramatically improve the ROI of your content marketing efforts. CanIRank is about helping you spend less time and money on traditional SEO activities like link-building and content promotion. Less SEO means less risk; so there’s no more living in fear of the latest Google algorithm updates or penalties. Most importantly, we hope CanIRank will enable you to spend more time doing what you do best — growing your business and delighting your customers — and less time trying to appease search engine robots.

Don't worry too much about pleasing robots.

Don’t become too focused on pleasing robots.

In order to achieve these goals, every piece of promotional content needs to earn its keep. There’s no point spending your valuable time writing a terrific blog post that no one will ever read. So how can we make sure that the website content you create gets noticed by both search engines and readers?

The answer requires flipping the traditional SEO process on its head: rather than creating a page and then trying to find ways to push it to the top, we will use CanIRank to ask the question: if I created a page about this topic on my website, what would it take to rank? By spending a few minutes more on upfront research, we can save hours of work later. No more “publish and pray”; instead CanIRank injects much-needed transparency and accountability into the content marketing process. For every piece of content you create you’ll have a reasonable idea of how much time and money it will take to rank well for that topic, and can adapt your content strategy accordingly.

A “New School SEO” Process with CanIRank:

Sound good? Great! Enough theory, let’s see how a New School SEO / Content Marketing process enabled by CanIRank might look in practice:

  1. Brainstorm keyword possibilities

  2. Narrow down keyword options to only those where our site is competitive

  3. Figure out what it would take to rank

  4. Generate an Action Plan for every keyword we want to target

  5. Create the content and follow the Action Plan until we rank!

Step 1: Brainstorm Keyword Possibilities

Brainstorm keyword ideas with Google Keyword Planner

Content Marketing works best if you’re not fixated on ranking well for just one or two keywords. Your first step should be to brainstorm as many different target keywords as you can think of. What types of questions do your potential customers have? What related information might they look for before making a purchase? Potential customers rarely use the “correct” vernacular: ask people outside of your industry what words they might use when searching for a business like yours.

If you run PPC ad campaigns (such as Google AdWords or Bing Ads), you can use the keywords from your paid search ad campaigns to inform your content marketing (organic or unpaid search) efforts. In fact, one of the best free tools for coming up with new keyword ideas is the Google Keyword Planner Tool. Enter a seed keyword or a URL and Google will suggest hundreds of related keywords, including the number of times that keyword is searched each month, an estimate of the cost per click (CPC), and an indicator of how competitive those ad placements are.

Step 2: Narrow Down the Keyword Possibilities

Use Ranking Probability score to narrow down your keyword possibilities

Hopefully you now have a list of Keyword Possibilities with dozens of topics that you might want to write about. Your next step is use CanIRank to narrow down the list to only those keywords where your website is currently competitive. (Don’t worry, as your website improves in authority, you’ll be coming back to the rest of those topics later.)

On CanIRank’s New Report page, enter a few of the keywords you’re interested in, and the URLs of a few pages on your website. Select “A page like” from the URL dropdown menu so that CanIRank knows you’re trying to evaluate the ranking potential of a similar page as if it were targeting that keyword.  Make sure you use URLs that are representative of the page you’ll be using to target this keyword. For example, if I’m researching a keyword for a new catalog page, I’ll include the URL of a few existing catalog pages. For a new blog post topic, I’ll enter the URLs for 3 or 4 of my existing blog posts. A good trick is to use one successful post, one average post, and one unpopular  post, so that CanIRank will return a range of Ranking Probability values representing “best case”, “typical case”, and “worst case” scenarios.

Try to find keywords with a Ranking Probability score in the 80s or 90s. These are the keywords where you’re most likely to be able to rank without having to spend a lot of time or money on promotion.

Step 3: Find out what it would take to rank

Use competitive analysis table to figure out what it would take to rank

Your list of Keyword Possibilities should now be down to the 3 or 4 keywords with the highest Ranking Probability score (hopefully 80% or better). Before you make a final selection, take a closer look at the Competitive Analysis table and “What do you need to improve…?” sections of the Report so that you can get a better idea of what really stands between you and a top ranking.

Are the existing rankers aggressively targeting this keyword by including it (or a variation) in their page title and content? (You’ll need more than good Page Relevancy to rank!) Is your Website Strength lower than most of the other rankers? (Choose a different keyword or be prepared for a long, slow process of building trust!) Do several rankers have low Page External Relevancy and/ or Page Strength scores? (That could be the weakness you need, since those scores are much easier to boost than Website Strength!)

Under the “What do you need to improve to rank better?” section, take note of any Ranking Factors where your URL scores below the minimum for all Rankers. Will you be able to easily increase that score to become more competitive? Click on the “Issues” button to get more specific details: are the Issues limited to one or two areas of weakness that you’ll easily be able to address?

Step 4: Generate an Action Plan

Action Plans are designed to address your site's weaknesses.

The deep dive into your website’s strengths and weaknesses vis à vis the competition should have enabled you to choose a target keyword with a relatively straightforward path to ranking. Now you’re ready for the fun part: taking action! Successful content marketing has two aspects:

  1. Thoughtful, creative content creation
  2. Effective content promotion

CanIRank is designed to help you with the second aspect, guiding you towards just the right kind of content promotion necessary to help your content rank well in the search engines and attract a steady stream of free traffic. These promotional activities are encapsulated in CanIRank’s Action Plan. Action Plans are a sequence of SEO and online marketing tasks designed to address the specific needs of your page, so each Action Plan focuses on a single URL competing for one keyword.

To generate a new Action Plan, click on the “Build Action Plan” button next to the URL that is most representative of the page you’ll be using to target this keyword. CanIRank will create the new Action Plan and take you to the “My Actions” page, where you’ll find your first few Actions. Each day you complete (or skip) Actions, CanIRank will generate a new batch of Actions focused on addressing the most urgent needs of your website (from the SEO perspective, at least). We recommend setting aside a little bit of time every day to complete an Action (or 2 or 3…), since small consistent effort will lead to much better results than sporadic spurts of heroic effort (which is not only less effective, it can sometimes lead to search engine penalties!).

Step 5: Create the Content and Promote Away!

Complete Actions and watch your rankings climb!

Creating a thoughtful and creative piece of content is perhaps the most important step of the entire process. The better job you do creating content that your readers find genuinely useful, interesting, and engaging, the easier you will find the content promotion activities to be. Spend some time putting yourself in the shoes of your customers and thinking about what they would find genuinely helpful. Time and money invested in quality writing, images, and web design acts like a lever to improve the effectiveness of your entire website, making it easier to attract links, keep visitors engaged, and convert browsers into paying customers.

After publishing your dazzling content and spending some time (perhaps 30 minutes/ day for a month) working through promotional Actions, if you’re still not ranking, you may want to try creating a new Report for the same keyword, this time selecting “Existing page” and entering the URL of the new page you’ve created. This Report will show you how your new page compares to the hypothetical model we analyzed previously, and may identify new Issues that you’ll want to build an Action Plan to address.

If you don’t see results right away, take heart: sometimes search engines take time to recognize improvements (especially in smaller websites), but as long as you keep doing the right things, eventually the rewards will catch up to your good efforts!