Keyword density has always been an important factor in on-page SEO. While stuffing your page with the same keyword over and over again used to work ten years ago, a too high or too low density could render your optimization efforts useless.

Semantically related words

End of 2006 marks an important moment in how search engines “view” and index your page. Google was the first to introduce the so-called “semantically related words” that gives webmasters an incentive to use natural sounding language. The concept is just a fancy word for saying you don’t have to re-iterate the same keyword throughout the text, since the spider will evaluate your page as a whole, figure out what it’s about and act accordingly. Latent Semantic Indexing (LSI) is one particular algorithm search engines use to indentify the semantically related keywords.

What it does for the site owner

Keyword stuffed articles look bad. Writing solely for search engines and not taking your (human) readers into account will make you lose your audience in the long run. Let’s illustrate this with an example of unnatural content:

The quick brown fox jumps over the lazy dog. Then, the quick brown fox jumps over that dog again. Finally, the quick brown fox runs back into the forest.

This would be a keyword stuffed paragraph, optimized for the phrase “the quick brown fox”. The following sounds much more natural:

The quick brown fox jumps over the lazy dog twice and then runs back into the forest.

LSI encourages webmasters to write naturally flowing content, i.e. articles that aren’t necessarily meant for web spiders. An LSI algorithm would figure out that the second sentence is about the quick brown fox and something it did and index it accordingly. Moreover, the spider can tell from a sentence like The German shepherd is playing with its owner that it’s about a dog, as opposed to a German person who herds sheep.

Why you need to understand about how LSI works

As already outlined above, search engines use LSI to understand what a page is about. A whole lot of on-page and off-page optimization factors are impacted:

• Inbound link relevancy. Using LSI, search engines can figure what the page that hosts your link is about and assess its power accordingly. If you run a tennis blog, a link coming from a sports authority will pass more juice than one from a gambling site.
• Outbound linking policies. Following the example above, linking from your tennis blog to a CNN piece of news about Rafa Nadal’s latest match would be perfectly understandable, while a link to spam directory is very likely to raise a warning flag.
• Loosen up with the on-page optimization. A keyword density of 2-3%—i.e. using a three word phrase 3-4 times throughout a 500 word article—can be done without jeopardizing readability. Use synonyms as well and the spiders will understand what your article is about.