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What is LSI and why it matters for SEO

Ibrahim Elsherbiny
I have been working within the SEO industry for 12 years now (since 2007). Today I run my own SEO Software known as SimilarContent. I help teach people SEO, as well as connect folks who need SEO services with expert consultants

Optimizing a website about ten years ago was all about using as many keywords as possible. Now, many experts in the SEO and content marketing community explain that keywords shouldn’t be the focus anymore.

They do matter, of course, but concentrating exclusively on keywords is a narrow approach to optimization. Instead, the smart use of keywords should be complemented by the smart use of LSI keywords, which can not only boost content quality, but also result in higher traffic, conversions, and rankings. 

But what exactly are LSI keywords and why is it important to include them in your content marketing strategy? Let’s find out. 

LSI – Definition 

LSI stands for Latent Semantic Indexing, a mathematical model developed in the 1980s to facilitate information retrieval. 

Why is a technology developed so many decades ago gaining traction now? Well, the technology has been used ever since, but it was only known to those who worked with natural language processing. 

What Latent Semantic Indexing does is that it helps put words in context by determining the relationship between words and concepts. Search engines use this technology to understand the content of each web page, index it, and then deliver relevant results to users, based on their search intent. 

In simple terms, LSI keywords are related words and phrases that are thematically related to your main keyword.

These words and phrases help make your content clearer, more relevant, and also help search engines deeply understand what your page is about. 

How does Latent Semantic Indexing work?

Imagine the word agile. In plain English, it means being able to move quickly and easily. However, if you capitalize it, Agile becomes a method of project management used in software development that splits tasks into short phases.

For search engines, understanding the difference between the two very different meanings of these words is very important if they are to retrieve relevant information for the user. So, how does LSI help them do that?

By using the context to create logical connections between concepts. 

For example, if a user looks up “agile animals” on Google, it’s clear that they’re interested in the common meaning of the word.

The user may be a student who needs help writing a biology paper, or just someone looking for fun animal facts. However, if the user searches for something like “agile and scrum”, “agile methodology” or “the 12 principles of agile”, then they’re interested in the specialized meaning of the word.

As you can see, the context and the words we use in combination with agile (even when it’s in lowercase) make all the difference. 

Let’s look at another example. Tesla. Depending on user intent, Tesla can refer to Nikola Tesla, the inventor, or it can refer to the popular car company.

To make the difference between the two, search engines scan for other terms in the text to give them a better idea of the topic.

If the text includes words like electricity, engineer, Serbian-American inventor, Edison, electricity, coil, or AC current, then it’s about Nikola Tesla the inventor. But if it includes electric car, stocks, Elon Musk, Cybertruck, Model S, or Roadster, then it’s about the car company. 

When indexing your pages, bots will obviously analyze the text for the main keyword, Tesla. But they will also scan it for related LSI keywords to have a deeper understanding of what it’s about and know how to recommend pages depending on their relevance. 

The evolution from keywords to natural LSIs

Let’s hop into the time machine and remember what it meant to optimize a web page for the keyword “shoes” back in 2010. In many cases, you would have stumbled about something like this: 

If you look closely, this text is about shoes. 

And it could have gone on for 500 words. Today, content of this type is no longer acceptable. It doesn’t read well, it doesn’t add value to the user, and you could have replaced “shoes” with almost any other word and it would have made just as much sense. 

Why did content look like this back in the day? Well, search engines are sophisticated now, but they weren’t always like this. About a decade ago, their algorithms weren’t that refined and they only looked at keywords when indexing pages.

So, if your page didn’t have the word “shoes” in it at the right density, it had fewer chances to rank in search engine results pages. 

This led to the now shunned practice of keyword stuffing, which gave us millions of pages of repetitive, generic content written entirely for search engines.

With time, search engines became more advanced and learned to understand natural language and conversational queries, making keyword stuffing not only obsolete, but also harmful. 

With updates like Panda, Penguin, and Hummingbird, Google moved away from keyword stuffing and started to mass-penalize websites that cluttered the same money term over and over. Modern search engines are much smarter and can’t be fooled as easily.

You don’t need to repeat plumbing services again and again for it to include you in SERPs. You can mention it a few times, and it will understand what your business does by analyzing related terms, such as burst pipe repairs or hot water system installation. 

By using main keywords less aggressively and including the right LSIs, you can first and foremost create more readable content that actually adds value to users.

Then, you avoid having your content being labelled as spam and visitors leaving your website too soon because they didn’t find what they were looking for. 

The transition from strict to natural search terms was also sped up by AI virtual assistants like Alexa, Siri, and Google Assistant, which are capable of understanding natural speech patterns. 

Keyword research vs. intent research 

Another important reason why search engines started to pay more attention to LSI keywords is that they help them understand search intent. 

Why does this matter? Because for several years now, the folks at Google have been very vocal about delivering more targeted, highly relevant results. 

So, with LSI, you cover not just the main keyword, but also the user’s intent when searching for it. There are four types of user intent: 

  • Informational: includes terms like who, what, where, why, how 
  • Navigational: usually includes website and company names because the user already knows where they want to go, but use the search bar instead of the address bar 
  • Transactional: includes terms like buy, coupon, sale, price, because the user already knows what they want and want to make a purchase 
  • Commercial: includes terms like review, opinion, best, top. The user has a general idea of the product they want to buy, but they haven’t decided on a final option yet. 

When writing content for your website, it’s essential to include LSIs that address user intent so that Google knows to display the content to relevant users.

Let’s say your main keyword is “sushi”. Using this keyword alone is not enough and you’ll need to add LSIs that give search engines a better idea of what you offer.

For example, if you have a recipe blog, then you’ll need LSIs like how to make sushi at home and homemade sushi recipes. But, if you have a restaurant, your LSIs will be more along the lines of sushi restaurant [+location], or sushi delivery [+location]. 

Knowing who your visitors are and what brings them to your website is the first and most important step in building a list of effective LSIs. 

LSIs vs. long-tail keywords vs. synonyms 

Most content marketers are now aware that keyword stuffing is a bad practice and they try to pay more attention to LSIs, but a common misconception is that LSI keywords are the same as synonyms or long-tail keywords. They’re not. 

A synonym is an equivalent of the main keyword (for example, financing instead of lending.)

A long-tail keyword is a phrase of at least three words containing your main keyword (for example, buy or rent commercial properties in Houston Texas)

An LSI keyword is a word or phrase that is related to your main keyword and pertains to the same field.

For example, if you have a digital marketing company, terms like call to action, click thru rate, cost per click, or pay-per-click advertising are all LSIs. As you can see, these terms aren’t long and they’re not synonyms either.

However, they fit in the context and help search engines understand your content better. In some cases, the three terms can overlap, but this isn’t a general rule. 

This isn’t to say that synonyms and long-tail keywords are not important. They are, and you should alternate between them to avoid spamming, but don’t think of LSIs as just synonyms or long-tail keywords because this approach is very limited and will have you miss out on many opportunities. 

Why does LSI matter for your website SEO? 

Now that you know what LSI keywords are and how search engines use them to display results, the question is: why should you bother using them? Do they really have an impact on SEO performance or are they just a trend that will go away soon? 

Yes, using the right LSI keywords can influence the way your website performs in search engines and, since their main goals revolve around context and relevance, we don’t see them going away any time soon. 

Increase content relevance 

As a brand, you want to get your message across accurately and be found on Google for the products and services you offer. Using only general keywords, without paying any attention to LSI, could create a lot of confusion because it doesn’t put your services in context and makes your message too vague.

For example, if you’re a photographer, you’ll want your content to include LSIs that give more information about what types of photography you offer. If you only do wedding photography, you don’t want search engines to assume that you also do commercial photography or food photography.

In the short term, you might be tempted to think that gathering a lot of traffic from everyone is good for you, but, as we’ll explain later, there is such a thing as useless traffic and quantity shouldn’t be your main focus here. 

Boost your TF*IDF score

TF*IDF stands for Term Frequency times Inverse Document Frequency and it’s a complex mathematical equation that determines whether you’re using a term too often or too rarely, based on the context in which it appears.

Words with high TF*IDF have a strong relationship with the target keyword they appear in. Although TF*IDF has nothing to do with LSI, it’s a metric that helps robots understand what your content is about. 

Increase readability 

Let’s recall the example with online shoes we mentioned in the beginning. Even a decade ago, when Google’s algorithms weren’t as sophisticated as they are today, that kind of text wasn’t popular among human users.

And it’s not hard to understand why. The mindless repetition of the same keyword again and again was bothersome on the eyes and the overall text didn’t add any value to the user.

People who clicked on an overly optimized page where the keyword “shoes” had been stuffed in the content dozens of times didn’t get any real, actionable information, they didn’t feel that their needs were understood or that they mattered in any way. 

By comparison, a carefully crafted piece of content where the use of keywords is alternated with the use of LSI is much easier to read and understand. Now, readability is a complex topic that includes many other factors, such as writing style and sentence length, but if you use the same keyword over and over, you won’t be able to maximize your score. 

Lower bounce rate 

What happens when the content people view isn’t relevant to their needs? They leave the website. And when that happens, the bounce rate increases. 

The bounce rate refers to the percentage of visitors who leave your website soon after clicking on it, without taking any action, such as making a purchase, subscribing, or clicking on more pages.

So, if you have thousands of views on a service page, but almost everyone leaves the page in less than one minute after viewing it, without making a purchase, this traffic doesn’t help you.

Granted, they could leave for many reasons, including that the page took too long to load or the design wasn’t user-friendly, but they could also leave because the service page they see doesn’t match what they were looking for. 

However, if you include more relevant LSIs in the content, you help Google match and rank you for the right keyword.

This way, visitors see content that matches their intent, they spend more time on your website and make purchases, thus lowering the bounce rate and increasing the conversion rate. 

Improve SEO performance 

Search engines are becoming more and more specific when it comes to analyzing and ranking content and they’re now looking for the best and most relevant content that they can display in response to a user query.

Search engines are likely to display the pages that include LSIs versus the ones that only include keywords, so you shouldn’t ignore them. Naturally, LSI keywords are not a quick hack or an easy fix. You still need to pay attention to what LSIs you use and how and, even so, content quality is measured by additional metrics too. 

How to find LSI keywords and use them in your content 

Some argue that if you know your field you will use the right LSIs naturally, and, to some extent, this is true.

If you’re an expert in FinTech, for instance, terms like Big Data, PCI compliance, peer-to-peer lending, underbanked, or User as Owner will naturally find their way into your content.

But can you know for sure that you included enough related terms and that you didn’t miss anything important? 

If you did, don’t you want to know what terms performed the best so that you can do that again for future content? 

Even if using LSIs is much less restrictive than using fixed keywords and sticking to a certain keyword density, it’s not a guessing game either, which is why you should know how to look for the most relevant LSIs and how to use them as part of your content. 

Use SimilarContent to find LSIs 

SimilarContent helps you create better, more effective, and more targeted content in two steps: 

  1. It checks your score against any search query, and then compares it to similar content on the web, including that of your competitors. 
  2. It suggests terms and phrases that you can include in your content so that you can increase keyword coverage and make it more optimized. The list of generated terms is based on the keywords and semantic variants used in the top-ranking pages of your focus topic. 

content keyword suggestion

SimilarContent’s Keyword Optimizer feature also helps you by retrieving search results and grouping them in related topics, so that you can better optimize your text to address search intent. The Keyword Optimizer suggests both main keywords, as well as closely related terms. 

The beauty of this service is that you can predict content performance before publishing it, and scan old content so that you can make it more relevant and possibly increase its rankings. 

Overall, SimilarContent makes it possible to gain total control of your content and use smart insights to boost its performance and surpass the competition. 

Place your LSIs in key positions

After you’ve made a list of relevant LSIs, placing them throughout the next might not look like a difficult task, but there are a few tricks that could boost performance: 

  • Include one or more LSIs in the title tag and description tag 
  • Add them in headings, where appropriate 
  • Make sure you have LSIs in the introduction (above the fold content is very important!) and conclusion
  • Add one LSI in the URL 
  • When building links, LSIs can be used as anchor texts 

If you’ve had a website for many years and worry that some of the content you wrote by old standards dangerously leans towards keyword stuffing, you can go over it and replace overused keywords with more natural phrases. While you’re at it, you should also consider expanding or refreshing that old content, so that you can get Google to crawl your website more frequently. 

Place LSIs naturally 

Although keyword density no longer exists, it’s difficult to get rid of old habits. Business owners who used keyword stuffing in the past still look at LSIs with a focus on quantity, not quality, and that’s not a good thing.

lsi content

The very purpose of LSI phrases is to make the content look more readable and more natural, so you shouldn’t try to force dozens of LSIs just for the sake of rankings.

We really can’t emphasize enough just how good Google has become at filtering relevant content from spam one and how quick it is to penalize bad practices through updates. 

So, once you’ve found a list of 100 effective LSIs that work for your competitors, don’t scatter them randomly in your content. They should belong in the text and make logical sense. Otherwise, they don’t address the user intent.

For example, if you’re going to include LSIs along the lines of best shooter games for Xbox but you don’t include any actual recommendations and notable releases, that kind of content isn’t useful, no matter how many other keywords it features. 

Analyze your content for SEO performance 

After you’ve drafted your content and hit publish, the optimization process isn’t over.

You’ll need to analyze that content to track top metrics, such as the sources from where you’re receiving traffic, the search phrases that people use to find your content, and how much time users spend on the website.

If the metrics are positive, you can continue with the same strategy. If not, you can continue to experiment with various strategies until you find the one that can drive growth. 

Conclusion

If your content optimization strategy revolves only around keyword research, now is the time to switch it up and consider the benefits that LSI phrases can have for your website.

In a time when search engines focus on user intent and natural language more than ever before, LSIs are becoming an essential part of SEO, so you shouldn’t ignore them, especially considering that tools like SimilarContent make them so easy to find. 

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