Website Content & Structure
The optimal keyword density doesn't appear to have changed but rather appears to have declined in value altogether. Sites with low keyword densities are starting to appear more often for phrases based more on their links than their content and also overall site relevancy.While the importance of a specific keyword density on a page has declined, this has been countered by an increasing importance of relevancy throughout the site. Google is opting to assign relevancy based more on the overall content of the site rather than a single page. General directories will be showing up less and less in exchange for topic-specific directories. Additionally, sites with a central theme carried throughout the majority of pages will tend to rank over sites with a specific page or even section on a topic.
Internal links are carrying a solid weight in attaching relevancy to specific internal pages. Properly worded internal links, preferably built into the content of your site (see note on natural links above) will add weight to those internal pages and increase the likelihood of those pages ranking for specific secondary phrases.
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