Google’s PageRank Algorithm: Explained and Tested
The Vice and Virtue of PageRank
By: Valerie Niechai
April 30th, 2019
Let me tell you a story. In the beginning was PageRank, and it made Google the most powerful search engine.
Everything was great till PageRank stayed the secret sauce of Google’s ranking mechanism and was talked about just in the research papers and technology pages.
However, once Google decided to make PageRank scores visible, it unleashed a flood of optimization strategies that were not exactly benign.
Let’s look into what PageRank was, what PageRank is, and decide whether it was a blessing or a disaster for the Web.
Definition of PageRank
PageRank (or PR in short) is a system for ranking webpages developed by Google founders Larry Page and Sergey Brin at Stanford University. It’s used to give each page a relative score of importance and authority by evaluating the quality and quantity of its links.
Here’s how it works. Each link from one page to another casts a so-called vote, the weight of which depends on the weight of the pages that link to it. And we can’t know their weight till we calculate it, so the process goes in circles. There should be hell of a formula to calculate it.
However, it’s much simpler than it seems.
Calculation of PageRank
Math is so cool that you can use a simple iterative algorithm and calculate the PageRank score of a page without knowing the value of other pages that link to it. How does it work? Each time we run the calculation, we are getting a closer estimate of the final value. We remember each calculated value and repeat the calculations a number of times till the numbers stop changing much.
In order to prevent some pages from having too much influence, the PageRank formula also uses a dampening factor. According to the theory, there’s an imaginary surfer who is randomly clicking on links, gets bored at some point, and stops clicking. The probability that this person will continue clicking at any step is a dampening factor. In the formula, the total value of pages is damped down by multiplying it by 0.85 (a generally assumed value).
It’s also considered that the average sum of all pages equals one. Thus, even if a page has no backlinks (i.e., no votes), it still gets a small score of 0.15 (one minus a dampening factor).
It’s believed that Google recalculates PageRank scores after each crawl of the Web. As it expands, the initial approximation of PageRank decreases for all documents. Most probably, PageRank favors older pages as new pages cannot have a big profile of quality backlinks, so they receive lower scores.
If you want to dig deeper into the algorithm, refer to this article by Ian Rogers that remains one of the best on the subject. As for the calculation details, read a detailed and digestible explanation of the calculation process by Dixon Jones.
The history of public PageRank (infographics)
When something is invisible, it doesn’t mean it doesn’t exist. The same goes for PageRank. Google took out the scores from the public access, but PageRank stays its secret sauce ingredient. What’s more, it still matters for rankings, as it helps the search engine determine the most relevant result for a particular query.
What’s more, PageRank hasn’t gone invisible in the minds of SEOs. You know how it goes: give something to an SEO, and he or she will reverse-engineer it. The exact same thing happened to PageRank. SEOs just didn’t want to stay blind to the important things happening behind the scenes. This way, a bunch of SEO houses (e.g., Moz, Ahrefs, Majestic, etc.) took the original PageRank formula as inspiration and developed alternatives to the metric.
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We in SEO PowerSuite also gave it a try and developed our own alternative — InLink Rank. Of course, we can never say that PageRank and InLink Rank are the same metrics. The only thing we can say for sure — InLink Rank is based on the original Google PageRank formula. The catch is in the fact that we don’t really know how exactly Google implements the formula.
We ran an experiment to find out whether Google still uses PageRank and which of the existing alternatives matches Google results best. As PageRank scores are generally associated with search positions, we’ve explored the possibility of a correlation between the alternative metric and SERPs. Let’s look at the methodology and results. For more details, come here.
InLink Rank and rankings correlation study
During three days, March 4-6, 2019, we looked at 30 Google search positions for 33,500 queries to get a list of 1,000,000 URLs. We recorded Domain InLink Rank for each URL. As a result, we had the raw data of one million rows to analyze.
Further on, we compared this data with the correlations for Domain Authority by Moz, Citation Flow and Trust Flow by Majestic, and Domain Rank by Ahrefs taken from a recent study by Moz.
As a result, we’ve been able to draw two conclusions:
- There is a high correlation between Google search positions and Domain InLink Rank – 0.128.
Analyzing the raw data, we saw that URLs with lower rankings tended to have lower Domain InLink Rank, and vice versa. Of course, it does not mean it always works like that — correlation does not imply causation.
- SEO PowerSuite’s InLink Rank has shown a 6% higher correlation compared to the next best metric — Domain Authority by Moz.
According to the similar analysis run by Moz, the strongest correlations between metrics and rankings were these (plus SEO PowerSuite’s correlation):
While there’s clearly a pleasant 6% stronger correlation with Domain InLink Rank comparing to the next best of Moz’ Domain Authority, we should note that our experiment hasn’t been performed using to the exact same methodology. It also doesn’t mean InLink Rank is an absolute factor — the correlation can vary for different niches.
However, you can see that the secret sauce ingredient wasn’t so secret after all — we were able to crack it and come close to Google’s calculations. It means you can safely use Domain InLink Rank as a reliable metric for evaluating the ranking potential of a domain.
1. While Google PageRank, now invisible to us, is still at the core of Google’s ranking mechanism, none of the industry metrics used in the analysis is directly used by Google and has any impact on rankings.
2. While PageRank alternatives used in the experiment are a good starting point for evaluating the ranking potential of domains, focusing on PageRank alone has never been a good SEO strategy. Likewise, a singular focus on any other metric won’t work out.
How to boost your PageRank score
Knowing that PageRank is still a part of the ranking mechanism is one thing. A completely different thing is to know how to influence it. Of course, no action can guarantee the increase of the actual PageRank score. However, we can monitor our SERP performance using alternative PR metrics (like InLink Rank) calculated according to the same approach.
Plus, we know two factors that hugely influence page’s credibility (thus, boosting PageRank flow to it):
- Quality backlinks
- Efficient internal linking
Let’s see how to optimize for each of these factors.
Backlinks carry link juice to your site. However, you need to make sure that this link juice is of high quality, otherwise, it can be harmful. To check links pointing to your site, run regular backlink audit. Here bear in mind that PageRank flows between pages, not domains. It means that links from a high-authority page on a low-authority site have more weight than links from a low-authority page on a high-authority site.
To make sure your backlinks won’t harm your site, check their InLink Rank scores in SEO SpyGlass. Run the tool, open or create a project for your site, and jump to the Backlinks tab.
Select those backlinks you’d like to check, click the Update button, and check the Backlink Authority box.
Once the analysis is complete, analyze the InLink Rank and Domain InLink Rank columns:
When the value of any backlink is low (marked by a red dot), it can be a strong indicator of a spammy or low quality link. You should run an additional check (described below). Note that new sites and small local businesses tend to have links with lower PageRank values, so you should consider getting rid of such links only when all the factors point to the fact they are spammy.
- Check for risks and errors
When you want to run an additional check for risks and errors, you need to pay attention to the page’s authority, nofollow tag, and anchor text. All these factors can be checked in SEO SpyGlass.
1) Go to the Penalty Risk dashboard, select those links you’re suspicious of, right-click them, and hit Update Penalty Risk.
In case you see some links having high Penalty Risk score, click on the “i” button to view Detected Penalty Risk factors:
2) In the same tab, check the Links Back column for the dofollow attribute, as it might be switched off:
3) Check the Anchor Text column in the Backlinks tab to make sure the texts haven’t been changed:
- Leverage linkless mentions
With a widespread use of a nofollow tag, how are search engines supposed to evaluate pages in terms of safety and relevance? Still carefully but we have a right to say that linkless brand mentions can be the future of link building. How come? Well, building linkless mentions is based on the same principles of credibility as building links. Plus, Google uses online brand mentions in its search algorithm. It evaluates your authority by looking at all the mentions of your brand and reputation around them.
Luckily, growing brand mentions is much easier than building links. Here’s what you need to do:
1) Find all mentions of your or your competitor’s brand from all over the web by creating an alert for a brand in a social monitoring tool, like Awario:
2) When you understand who is talking about your or your competitor’s brand online, use the following tactics:
- Jump into conversations and mention your brand whenever it’s suitable (e.g., when your product or service can come in handy in a given situation);
- Try to keep your customers engaged to make them talk about your brand (e.g., solve their problems, run contests, etc.);
- Track industry keywords to understand your niche better and find those who can spread the word about your services to your audience.
Efficient internal linking
Link building is a time-consuming activity, and it can get out of hand. Thus, backing up your PageRank flow by efficient internal linking is a nice strategy, as internal linking is totally in your hands.
- Keep your site structure shallow
As confirmed by John Mueller during one of the Google Webmaster Central hangouts, keeping any page 2-3 clicks away from the homepage is highly recommended. If your site is so huge that 2-3 clicks cause a nervous laughter, use breadcrumbs and internal search to make your site’s browsing easier.
- Make sure there are no orphan pages
Orphan pages are those not connected to any other page on your site and thus invisible to Google. It means no link juice for them. The most important thing is to check that no important pages of yours have become orphans.
You can either check the click depth of your pages in WebSite Auditor’s Site Audit dashboard or go straight to the Visualization tab. Once your site structure is visualized, check for the nodes that are not connected with any others. These are your poor orphans.
- Add links to your page’s main content
When you interlink content within your site, mind that link location influences its SEO value. Links placed within main content are considered to be more valuable than those in the navigation elements.
- Include keywords in your anchor texts
Tell your readers what to expect if they follow your hyperlinked text. One or two keywords in your anchor text won’t be viewed as keyword stuffing. The same goes for alt attributes for your images that serve as anchors for text.
- Keep an amount of links per each page reasonable
Google Webmaster Guidelines say the number of links per page should be reasonably limited. It maintains the readability of pages and protects your pages against spam flagging. Plus, remember if you link to one and the same URL a few times on the same page, only the first anchor text will have an SEO value.
PageRank definitely made a dent on the world as it helped Google become the search giant, and it still remains a part of its search algorithm. However, it’s important to remember there are hundreds of other ranking factors. What makes pages rank higher is a combination of the factors, which can be different for each page. There’s no sense in focusing on just one factor. Instead, take a holistic approach to your SEO activities to find a happy medium.
By: Valerie Niechai