Why Technical English

Who else will discuss PageRank calculations?

April 3, 2012
16 Comments

Composed by Galina Vitkova

Procedure of calculations

In the field of information retrieval on the web, PageRank has emerged as the primary (and most widely discussed) hyperlink analysis algorithm. But how it works still remains an obscurity to many in the SEO online community.

PageRanks-Example

Nevertheless, regarding to the importance of PageRank it worth trying to examine or analyse how it is calculated. The study is meaningful even if Google keeps the real algorithm of PageRank calculations secret.

In any case PageRank calculations are performed in compliance with The PageRank Algorithm

Let us consider the example consisting of  4 pages: Page A, Page B, Page C and Page D (or simply A, B, C, D having their PageRanks with the same notation). The pages link to each other as shown in the following picture. In the beginning the PageRanks for the pages are unknown, so we’ll just assign „1“ to each page.

 Linking of four pages

It means that the first calculation begins with PageRanks as follows:

  A = 1    B = 1    C = 1    D = 1

According to the rules about passing rank, which come out from the mentioned formula, each page passes a part of its PageRank to other pages. So, first we apply the dampening factor “d”, which ensures that a page cannot pass to another page its entire PageRank. Then the remaining value is divided by the number of links outcoming from this page. Finally the entire ranking is summed up and added to each page. In the first table below you see the value of PageRanks passing from one page to another:

A (2 links)  = 1*0.85 / 2 = 0.425
passes  0.425 to B
          0.425 to C
B (1 link)    = 1*0.85  = 0.85
passes  0.85  to  C
C (1 link)    = 1*0.85  = 0.85
passes  0.85  to  A
D (1 link)    = 1*0.85  = 0.85
passes  0.85  to  C

The resulting PageRanks are depicted in the following table below:

A = 1 + 0.85 = 1.85
B = 1 + 0.425 = 1.425
C = 1 + 0.425+0.85+0.85 = 3.125
D = 1

So, the next run of calculations begins with:

A = 1.85    B = 1.425    C = 3.125    D = 1

And after performing the same operations it comes to the result as follows:

A = 4.50625     B = 2.9975    C = 5.18625    D = 1

In practice it is necessary to do identical operations 50 to 100 times to guarantee the sufficient accuracy of the iterations.

Here needful to notice that in the first run of the calculations, Page C increases PageRank of Page A. In the next run Page C gets itself an increase in PageRank that is proportional to the new improved PageRank of Page A. It means Page C gets a proportion of its PageRank back to itself. It is PageRank feedback, an essential part of the way how PageRank works.

Links to and from your site

PageRank is the hardest factor to manipulate when optimising your pages. It is both difficult to achieve and more difficult to catch up with.

GoogleBot-byFML

When trying to optimise your PageRank the following factors should be taken into consideration:

  • Choice of the links you want to link to your site;
  • Selection of a site you want to link out to from your site;
  • Production of maximum PageRank feedback by changes of the internal structure and linkage of your pages.

When looking for links to your site, from a purely PageRank point of view, the pages with the highest Toolbar PageRank seem to be the best solution. Nonetheless, it is not truthful.

As more and more people try and get links from only high PageRank sites, it becomes less and less profitable. Thus sites that need to improve their PageRanks should be more receptive and exchange links with sites that have similar interests. Moreover, the number of links on the page linking to you will alter the amount of feedback, etc.

Therefore, maybe the best solution is getting links from sites that seem appropriate and have good quality, regardless of their current PageRank. The quality sites will either help your PageRank now, or will do so in the future.

To consider the best strategy concerning links out from your site, the general rule is: keep PageRank within your own site. Control of feedback by using the internal pages of your site, is much easier than control with the help of links to external pages. It means to make links out from a page on your site that has a low PageRank itself, and which also contains many internal links. Then, when linking out choose those external sites, which do not point to your page with a significant number of links.  It will get a better increase in PageRank, in particular due to the power of feedback. 

Placing some your links back into your site system rather than letting it go to external links improves PageRanks of your pages. That is why larger sites generally have a better PageRank than smaller ones.

References:

 

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