Page Rank Explained

What is PageRank?

PageRank is a measure of the importance of a webpage based on the number of links to that page from other websites. It is named after Larry Page who developed the algorithm while at university, hence the name PageRank.

When the PageRank algorithm analyses incomming links to a webpage, it also takes into account the importance of those pages from which the incomming links are comming from. In this way, the importance of a new webpage not only depends on the number of links pointing to it from other websites, but also google’s measure of importance of those websites. This makes the PageRank algorithm resistent to black hat manipulation.

The PageRank of a website can be seen from the PageRank component of the google toolbar. Pages that tend to appear in the first 3 pages of search engine results pages will tend to have a higher pagerank relative to the websites that appear further down in SERPs. A high pagerank is relative to the pagerank of competitors for the keywords that you are aiming to promote, and therefore if your ecommerce website has a google pagerank of 3 or 4, and your main competitors have a pagerank of 2 or 3, then you are doing well in regards to your site’s pagerank. PageRank is not the only factor that determines your ecommerce website’s position in search engine result pages either and you may occassionally find lower pageranked sites fairing well in positioning.

Not all links are counted by Google and it often filters out links from unreputable directories that are associated with spam. Similarly if your ecommerce website links to sites that have a bad reputation (usually indicated by a pagerank of 0) then google may penalise your ecommerce site for endorsing a poor quality website.

How is PageRank calculated?

To calculate a simplified PageRank for a page ‘A’, all of its inbound links are taken into account. Assuming that there are three inbound links from webpages ‘B’, ‘C’ and ‘D’ and that there were no other webpages on the internet, then ‘B’, ‘C’ and ‘D’ would each propagate a PageRank of 25% to page A and A would have a pagerank of 100% or 10/10. PageRank is therefore a type of probability distribution.

If page B were also to have links to C and page D has links to A, C and B, then the inbound link to A from B would be halved to 0.125 and the inbound link from D would be cut by a third to 0.083, giving page A a pagerank of 0.5 or 5/10. Therefore the pagerank that is gained from an inbound link also depends on the pagerank of the link’s page and the number of outbound links from that page. From this, we could conclude that a link from a page with PR4 and 5 outbound links is worth more than a link from a page with PR8 and 100 outbound links. The PageRank of a page that links to yours is important but the number of links on that page is also important. The more links there are on a page, the less PageRank value your page will receive from it.

Note that when a page votes its PageRank value to other pages, its own PageRank is not reduced by the value that it is voting. The page doing the voting doesn’t give away its PageRank and end up with nothing. It is simply a vote according to the page’s PageRank value.

A disadvantage of PageRank is that it favours old pages that have many links pointing to it rather than new pages that do not have many links pointing to it. Luckly PageRank is not the only factor that determines the position of a page on a serch engine results page. The only place where pagerank absolutely determines positioning is in the Open Directory Project (google directory). The exact mechanisms that determine a page’s position in a search engine results page are trade secrets of google.

The maximum amount of PageRank in a site increases as the number of pages in the site increases and the number of inboud links increases.

There are certain types of pages that should not be added such a duplicate pages or pages that are taken off other websites. Google considers them to be spam and they can trigger an alarm that causes the pages, and possibly the entire site, to be penalised. Therefore a site must grow with orignal content.

Domain names and Filenames

To a spider, www.domain.com/, domain.com/, www.domain.com/index.html and domain.com/index.html are different urls and, therefore, different pages. Surfers arrive at the site’s home page whichever of the urls are used, but spiders see them as individual urls, and it makes a difference when working out the PageRank. It is better to standardize the url you use for the site’s home page. Otherwise each url can end up with a different PageRank, whereas all of it should have gone to just one url. Standardizing the home page’s url ensures that the Pagerank it is due isn’t shared with ghost urls.

Sub-directories

Some people believe that Google drops a page’s PageRank by a value of 1 for each sub-directory level below the root directory. E.g. if the value of pages in the root directory is generally around 4, then pages in the next directory level down will be generally around 3, and so on down the levels. It is generally considered to be beneficial to keep directory structures shallow (directories one or two levels below the root).

ODP (Dmoz) and Yahoo!

It used to be thought that Google gave a Pagerank boost to sites that are listed in the Yahoo! and ODP (a.k.a. DMOZ) directories, but these days general opinion is that they don’t. There is certainly a PageRank gain for sites that are listed in those directories, but the reason for it is now thought to be this:-

Google spiders the directories just like any other site and their pages have decent PageRank and so they are good inbound links to have. In the case of the ODP, Google’s directory is a copy of the ODP directory. Each time that sites are added and dropped from the ODP, they are added and dropped from Google’s directory when they next update it. The entry in Google’s directory is yet another good, PageRank boosting, inbound link. Also, the ODP data is used for searches on a myriad of websites – more inbound links!

Why does a lower PageRank page beat mine?

PageRank on its own does not decide a page’s ranking in the search results. If it did, we would have the situation where all PR10 pages would be displayed at the top of the search results, regardless of the search term used. All PR9 pages would follow those, and so on.

Google uses dozens of factors to determine the rankings, such as Title text, body text, inbound link text and PageRank. PageRank isn’t even the most important factor. It is often the case that pages beat higher PageRank pages because they are better optimized across the various factors for the particular search term.

One important reason why an on-topic page could beat an on-topic page with a higher PageRank is the inbound link text. Google assigns link text to the receiving page. It is as though the link text is on the receiving page, and it views it as being important to the receiving page. It may be that the link text on most or all of the pages that link to the lower PageRank page includes the actual search term, whereas most or all of the link text on the pages that link to the higher PageRank page may not include the search term.

Inbound links tell Google how important the page is; inbound link text tells Google what the page is important about – from the linking pages’ viewpoint.

The fact that a page has a higher PageRank doesn’t mean that it has more inbound links than a lower PageRank page. It may only have a few, all from high PageRank pages, whereas the lower PageRank page could have a lot more inbound links, but from lower PageRank pages. The lower PageRank page could have a far greater potential for search term rich inbound links, and could beat a higher PageRank page on account of them.

There are many reasons why pages beat higher PageRank pages in the search results. The important thing to realize is that PageRank on its own doesn’t determine rankings.

Why has my PageRank gone down?

When a page drops several Toolbar points, often to PR0, it is the result of a penalty, though not necessarily a penalty that has been applied to the page itself or even to the website. Penalties are applied when Google finds things about a website or page that they don’t like. E.g. involvement in link farms, doorway pages, multiple domain techniques, hidden text, cloaking, etc.

Link penalties: Google’s view is that webmasters cannot control which websites and pages link to their sites, but they can control where their own sites links to. Linking to a penalized page or site, or a page or site that is later penalized, can attract a penalty for the linking site.

It is possible to find a reduction in the Toolbar figure following the update after making internal link changes. I.e. by changing linkages, it is possible to divert the PageRank within the site to different pages.

Why have my pages disappeared from the search results?

There are a number of reasons why pages disappear from Google’s search results. Here are some of them:-

Occassionally pages, and whole websites, vanish from the search results following an update, but are restored after the next update. Google continually tweak the way they evaluate and rank pages and, sometimes, glitches occur. Sites and pages even get a PR0 as the result of a glitch, although usually PR0 indicates a penalty. Glitches are usually corrected at the next update.

New pages are given temporary evaluations and placed (ranked) in the search results. These are temporary rankings and a very unstable. For a new page to ranked correctly, it needs to be in Google’s main index. For that to happen the page needs to be crawled in Google Main Crawl, and then go through the following update. If a new page has only been Fresh Crawled (see Fresh Crawl), its rankings in the search results are not based on a full evaluation of the page, and are very volatile. They can appear, disappear, change position, and can even have other pages of the website taking their place for a while.

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2 Responses to “Page Rank Explained”

  1. Really useful article and very helpful thanks

  2. Stinky10 says:

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