Because Google and other search engines are using LSI to decide the relevance of your words to your subject matter. This obviously determines how much traffic you can expect from search engine results.
If you're still using old-fashioned keyword density analysis (KDA) to optimize your on-page factors, Google is way ahead of you. With LSI, Google and other search engines figure out what your page is about based on the other important words you use, plus checks for words that commonly appear in other content related to your site -- NOT by the percentage amount you use your targeted keyword.
So what is Latent Semantic Indexing (also known as Latent Semantic Analysis)?
On a technical level, it's computers using complex mathematical models to figure out what text in documents means. This article doesn't pretend to explain the equations that make it work.
The real question is, what does LSI mean to us web content writers? How can or how should we be using LSI to make Google rank us higher?
Basically, LSI can use the other words in your page to help it figure out what your site is really about. This helps solve the problem of synonyms (where two or more words can mean much the same thing) and polysemy (where one word can mean more than one thing).
Also, using LSI, Google can compare the vocabulary of your page to the words used on all relevant websites -- and all the books in its database. Therefore, you're compared against authority sites and the experts who've written "real" books!
So how can you use LSI?
When you write, use your keywords in a natural way -- and also all related and "expert" vocabulary.
If you're writing about lemon pie instead of lemon poor quality cars, make sure you include the relevant vocabulary of pies instead of cars.
If you're writing about Jaguar the car make sure you include the details that will distinquish it from jaguar the big cat and Jaguar the Mac OS X computer operating system. Don't just use "Jaguar" in isolation.
Include relevant synonyms and other expert vocabulary.
With keyword density analysis you avoid synonyms and repeat the targeted keyword to reach the (supposedly) optimal density percentage.
With LSI, you include your main targeted keyword but as the top of a pyramid of synonyms and relevant expert vocabulary. The more you write like an expert on a given subject, the higher you'll rank.
After all, Google wants to give its searchers the best, most expert web sites. So write with the vocabulary of an expert even if you aren't one.
What's the first step?
Before you write anything, do keyword research -- but not in the usual way. Think about synonyms. Common sense and your own basic knowledge of the subject comes first.
Then go to Google and put your main keyword into the search box with a tilde sign (~) in front of it. The results will then include what Google regards as synonyms to your keywords -- they'll be in boldface type.
Repeat with the synonyms you bring up.
Go to the top sites and look for the keywords in their meta tags and look for the expert vocabulary they use in their content.
Do the same ~Google search on those keywords.
Soon you'll have a large list of terms relevant to your main keyword. Include as many of them as possible in your sales letter or web article.
Of course, make everything sound natural and well-written to your reader.
