| In the SEO realm there is a lot of focus on PageRank as an indicator of a domain's worth. Although it is probably one of the most important aspects of a domain's worth in the eyes of Google, there are a few details that should be understood.
Google PageRank has eleven values, between 1 and 10. This holds true for both external and internal links. The higher the PageRank, the more likely Google is to trust it. Google assigns each page on the internet a score and when one web page links to another it passes some value onto the page it is linking to. First of all, for anybody who doesn't know what PageRank is - it is a score used by Google to decide how important a domain is based on analysis of hyperlinks. Web pages that don't have any PageRank are often symbolised as having N/A PageRank.
Probably the most important factor in the distribution of PageRank to a web page is the PageRank of the pages linking to it. So, if a page has 4 PageRank 4 and 3 PageRank 3 links pointing at it, it will probably be assigned a PageRank of 4. PageRank is generally not assigned to a page higher than the pages that link to it. In addition, pages that have a lot of low PageRank and PageRank N/A hyperlinks pointing to them can have their PageRank lowered as a result. The higher the PageRank of web pages linking to a given page, the higher its PageRank is likely to be. Sheer quantity of links does not help to increase PageRank. A site can have a high PageRank with relatively few links pointing to it if those links are of a high PageRank.
Some suggest that the text content of the page affects PageRank assignment, but this doesn't seem to be the case. There is no substantiated evidence that text affects PageRank other than pages that have been spammed often have their PageRank reduced.
When it come to sub-pages, time is a factor in PageRank assignment. When new sites first get assigned PageRank their sub-pages often remain without any PageRank. In general, sub-pages are a little slow to get give PageRank. Google is generally less trusting of sub-pages unless they belong to a trusted domain. In particular websites with a lot of sub-pages and even more so sites that link to a lot of internal pages (like directories) can struggle to pass their PageRank to internal pages.
The architecture of the site has a major role to play in the distribution of PageRank. Google uses what is known as block level analysis to analyses web pages. They use their vast knowledge of the structure of the web to decide what links on a page are probably the most trustworthy and the pages these links point to are more likely to receive PageRank.
Google can and do modify websites' PageRank. This is generally as a penalty for sites that have used unhonest practices. This can often cause all the site's sub-pages to loose their PageRank. It has also been claimed that in the past Google has made mistakes in PageRank assignment.
Finally, the PageRank of a web page may change even when there has been no change in the hyperlinks pointing to that page. This is either due to changes in the structure of links between all websites or modifications made by Google.
Sky Alfaro is an SEO consultant with the SEM Labs SEO Agency where she helps small to medium sized companies with search engine marketing training. |