What is Latent Semantic Indexing, and Why is it Important?

– Posted in: Keywords, SEO

What is Latent Semantic Indexing (LSI)?

Latent Semantic Indexing (LSI) is one way that search engines analyze your content and ascertains that it is on topic and not spam. Search engine algorithms determine this by taking all words in your article and determining how relevant they are to each other. Ergo, if your article is about losing weight, for instance, the search engine will understand that the words in your article should closely relate to “losing weight”. It looks for words that pertain to losing weight, such as weight loss, diet, exercise, eating right, etc. These are latent semantic indexing terms.

What Search Engines do when they find your article?

  1. It reads your article.
  2. It evaluates keyword density of each word or phrase in your post. It takes all the words of your post and counts how many times particular words or phrases repeat in the article. Words and phrases that repeat more often have a higher keyword density. This is how the search engines determine the topic of your article. Say for instance that your article is about “fast weight loss.” Let’s also say your article has 1,000 words and the phrase “fast weight loss” shows up 5 times in that article. That would give your article a word density of about 1.5% (15/1000 x 100 = 1.5%). I’m using 15 because “fast weight loss” has three words in the phrase; the three words appear five times, which equals 15. It also helps the search engine determine what your article is about if you use the key phrase as your title, as a paragraph heading, and within several paragraphs.
  3. To search engines, your article is about whatever the highest keyword density is, or by what its relevancy score is. In our example, if the search engines find a high keyword density for “losing weight,” it then knows to expect high densities for other terms like, weight loss, dieting, exercise, and eating right.

Why Latent Semantic Indexing (LSI) is Important for your Website

With all the information out there today, search engines have become very smart. They know what to expect for most related keywords and phrases. Therefore, if they expect to see certain related keywords, but don’t find them, they will give a lower relevancy score. The relevancy score is what places your article at the top of the Search Engine Results Page (SERP). Consequently, the lower relevancy score will directly affect where that article ranks in the SERPs.

Latent Semantic Indexing is one key concept to search engine optimization (SEO). Search engine algorithms are getting smarter every day. Moreover, having a good balance of latent semantic indexing terms with the main topic of your article proves to be rewarding in search engine results.

In the next article that you write, consider the whole picture from reader to search engine. Make it read well to humans, and be certain that the article has a good density of keywords that are relevant to your topic for good search engine optimization.

1 comment… add one
Nikolay Stoyanov March 29, 2016, 2:36 am

Heidi, I enjoyed your LSI article a lot. This is still a considerably unknown topic and I always love reading more about it.

I liked your search engine example too.

Keep up the great work!


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