PageRank is what Google uses to determine the importance of a web page. It's one of many factors used to determine which pages appear in search engine result page (SERP) and how it crawls websites.
The link analysis algorithm was named after Larry Page in 1996, and used by the Google web search engine, that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of measuring its relative importance within the specific niche. The algorithm may be applied to any collection of entities with reciprocal links and references.
First implemented and patented at Stanford. At the time that Page and Sergey Brin met, search engines typically linked to pages that had the highest keyword density, which meant people could cheat into the system by repeating the same phrase over and over to attract higher search page results.
A PageRank results from a mathematical algorithm based on the webgraph, created by all World Wide Web pages as nodes and hyperlinks as a way to jump from one page to another. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it (incoming links or backlinks). A page that is linked to by many pages with high PageRank receives a high rank itself. If there are no links to a certain page, then there is no purpose to rank and support that page.
Numerous academic papers concerning PageRank have been published since Page and Brin's original paper. In practice, the PageRank concept is vulnerable to manipulation. Research has been conducted into identifying falsely influenced PageRank rankings. The goal is to find an effective means of ignoring links from documents with falsely influenced PageRank.
The SERP is the actual result returned by a search engine in response to a keyword query. The SERP consists of a list of links to web pages with associated text snippets. The SERP rank of a web page refers to the placement of the corresponding link on the SERP, where higher placement means higher SERP rank. Search engine optimization (SEO) is targeted at influencing the SERP rank of websites and web pages.
Positioning of a webpage on Google SERPs for a keyword depends on relevance and reputation, also known as authority and popularity. PageRank is Google’s indication of its assessment of the reputation of a webpage: It is non-keyword specific. Google uses a combination of webpage and website authority to determine the overall authority of a webpage competing for a keyword.
The word PageRank is a trademark of Google, and the process has been patented.
PageRank Measurements
Google PageRank measure's a web page's importance. Page and Brin's theory is that the most important pages on the internet are the pages with the most links leading to them. PageRank thinks of links as votes, where a page linking to another page is casting a vote.
PageRank also looks at the importance of the page that contains the link. Pages with higher PageRank have more weight in "voting" with their links than pages with lower PageRank. It also looks at the number of links on the page casting the "vote." Pages with more links have less weight.
Pages that are important are probably better authorities in leading web surfers to better sources, and pages that have more links are likely to be less discriminating on where they're linking.
PageRank Importance and Flaws
PageRank is one of many factors that determines where a web page appears in search result ranking, but if all other factors are equal, PageRank can have significant impact on Google rankings.
Although PageRank keeps developing, it certainly still have flaws. Now that people know the secrets to obtaining a higher PageRank, the data can be manipulated. Google Bombs are a classic example of PageRank manipulation. "Link farming" is another method people attempt to use manipulate PageRank. Link farming is the practice of linking without thought of the relevance of the pages being linked, and it's often automated.
For SEO purposes, some companies offer links exchange and/or sell links with high PageRank to webmasters and web owners. As links from higher PageRank pages are said to be more valuable, they tend to be more expensive. It can be an effective marketing strategy to buy link advertisements on content pages of quality and relevant sites to drive traffic and increase a link's popularity. However, Google has warned webmasters that if they are or were discovered to be selling links for the purpose of conferring PageRank and reputation, their links will be devalued.
The practice of buying and selling links is intensely debated across the Webmaster community.
PageRank Scale
PageRank is measured on a scale of "unranked" and one to ten. This is assigned to individual pages within a website and not the entire website.
Unranked pages are pages that are relatively new and have no links and importance to Google. Very few pages have a PageRank of 10, especially as the number of pages on the internet increases.
Increasing PageRank
Backlinks and the actual information within the page that have high measurement of attractiveness are two of the way to increase PageRank. To make backlinks, make sure that the links traded are relevant, and make sure that it's not traded with a link farm. Registering the website to web directories is one example.
As a website have more pages, the website can create some of its own backlinks by linking to relevant pages within its site. However, the number of links created counts into the equation so it's necessary to not overdo it.
The best way to increase a PageRank is to have quality content that other people want to link.
Google now also relies on other strategies as well as PageRank, one of them is the Google Penguin.
PageRank and NoFollow
In early 2005, Google implemented "nofollow" value for the rel attribute of HTML link and anchor elements. This is done so web developers and bloggers can make their links not considered by Google and will make it ranked by PageRank. The value in the link makes it no longer constitute a "vote" in the PageRank system. The nofollow relationship was added in an attempt to help combat spamdexing.
In an effort to manually control the flow of PageRank among pages within a website, many webmasters practice what is known as PageRank Sculpting - which is the act of strategically placing the nofollow attribute on certain internal links of a website in order to drive PageRank towards those pages the webmaster deemed most important. This tactic has been used since the inception of the nofollow attribute, but may no longer be effective since Google announced that blocking PageRank transfer with nofollow does not redirect that PageRank to other links.