PageRank

Each “follow” link to a page is counted by Google as a vote of support. The number of links to the page tells about its importance. One of the ways measuring a page's importance by Google Search is determining its PageRank.

PageRank is a measure of page’s importance within the set of linked pages. An algorithm used for determining the PageRank assigns a numerical weighting to each element of a hyperlinked set of documents in the World Wide Web.

In the algorithm of PageRank calculation, links from all pages are not count equally. If page A has links from pages T1, ..., Tn, the PageRank of a page A was originally defined by the function1:


PageRank algorithm

For example, there are three pages that are linked on this way:

An example of the pagerank calculation

Theoretically, we can calculate the PageRank for each of those pages:

PR (A) = (1 – d) + d [PR(C) / C(C)] = 0.15 + 0.85 PR(C);
PR (B) = (1 – d) + d [PR(A) / C(A)] = 0.15 + 0.85 (PR(A) / 2);
PR (C) = (1 – d) + d [PR(A) / C(A) + PR(B) / C(B)] = 0.15 + 0.85 (PR(A) / 2 + PR(B)).
But, we don’t know what the PageRank should be used to begin the calculation. We only know that “PageRanks form a probability distribution over web pages, so the sum of all web pages’ PageRanks will be one.”1



We also know that the more pages linked to a particular page, the higher PageRank this page has. A page can have the high PageRank if there are many pages point to it or there are some pages with the high PageRank point to it. It is because with a “follow” link to your page from another page, some of its PageRank importance is transmitted to your page.

An example of the page importance



Google counts the PageRank to know what pages are the most important and combines PageRank with other techniques to find pages on the Web that are both important and relevant to user’s search query. “We assess the importance of every web page using more than 200 signals and a variety of techniques, including our patented PageRank™ algorithm, which analyzes which sites have been “voted” to be the best sources of information by other pages across the web.”2

The PageRank you see in the Google Toolbar, an Internet browser toolbar for Internet Explorer4, is not calculated by using the PageRank™ algorithm. Google has divided all actual PageRanks into 10 parts each from which is represented in the toolbar by a part of the rectangle colored in green. Google in its toolbar only shows the part of the overall range the page's PageRank is in, and not the actual page's PageRank. The higher number of the part, the bigger piece of the rectangle has the green color.

An example of the Google Internet Explorer Toolbar


A similar PageRank tool button is present in Google Chrome:

An example of the Chrome SEO Toolbar



If you have the Google toolbar installed in your browser, you will see PageRank for each page as you browse the web. And all the time, a number on the tool button will be just an indicator which only shows that a current page is in a certain range of the overall scale. For example, the number 3 will tell that the current webpage is in the section between the PageRank 3 and PageRank 4.

Some notes about PageRank:


When one your page links to another page, it “votes” for another page.

In other words, your page gives another your page some amount of rank credits.

The more pages your website has the better.

The more pages your website has the more "votes" some of your pages might have. 

PageRank is a numeric value that indicates how important a page is on the Web.

You should sculpt your PageRank to the TOP pages.

You should build your website in such a way so your TOP pages will receive the most rank credits from all other pages on your website.

PageRank is only one of many factors used to determine the page’s search ranking.

In its philosophy, Google tells that it is using more than 200 different signals for determining the page's search ranking, and PageRank is only one from them.

PageRank is never known exactly.

PageRank says nothing about the content and size of the page, the language it is written in, and the text used in the anchors of links.

The page's PageRank only shows "votes" of support by other pages on the Web.

High PageRank doesn’t guarantee a high search ranking for any particular term.

Otherwise, websites with the highest PageRanks such as Adobe, Google or Wikipedia would always be shown in search results for any user's search.

The link's anchor text might be more important than the page's PageRank.

If your page has an external link to a page on another website, your page “votes” for that page, consequently, gives some rank credits another website.

If you don't want your page gives ranking credits another website, you should add to your <a> tag the rel="nofollow" attribute.

References:

1. “The Anatomy of a Large-Scale Hypertextual Web Search Engine” Sergey Brin and Lawrence Page. 8 November 2015 < http://infolab.stanford.edu/pub/papers/google.pdf >
2. “Ten things we know to be true” Google Company. 10 November 2015 < http://www.google.com/about/company/philosophy/ >
3. “The PageRank Citation Ranking: Bringing Order to the Web” 29 January 1998. 10 November 2015. < http://ilpubs.stanford.edu:8090/422/1/1999-66.pdf >
4. “Toolbar Help” Google. 2015. 10 November 2015. < https://support.google.com/toolbar/answer/9171?hl=en&ref_topic=3338372 >
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