I recently came across an SEO test that attempted to verify whether compression ratio affects rankings. It seems there may be some who believe that higher compression ratios correlate with lower rankings. Understanding compressibility in the context of SEO requires reading both the original source on compression ratios and the research paper itself before drawing conclusions about whether or not it’s an SEO myth.
Search Engines Compress Web Pages
Compressibility, in the context of search engines, refers to how much web pages can be compressed. Shrinking a document into a zip file is an example of compression. Search engines compress indexed web pages because it saves space and results in faster processing. It’s something that all search engines do.
Websites & Host Providers Compress Web Pages
Web page compression is a good thing because it helps search crawlers quickly access web pages which in turn sends the signal to Googlebot that it won’t strain the server and it’s okay to grab even more pages for indexing.
Compression speeds up websites, providing site visitors a high quality user experience. Most web hosts automatically enable compression because it’s good for websites, site visitors and also good for web hosts because it saves on bandwidth loads. Everybody wins with website compression.
High Levels Of Compression Correlate With Spam
Researchers at a search engine discovered that highly compressible web pages correlated with low-quality content. The study called Spam, Damn Spam, and Statistics: Using Statistical Analysis to Locate Spam Web Pages (PDF) was conducted in 2006 by two of the world’s leading researchers, Marc Najork and Dennis Fetterly.
Najork currently works at DeepMind as Distinguished Research Scientist. Fetterly, a software engineer at Google, is an author of many important research papers related to search, content analysis and other related topics. This research paper isn’t just any research paper, it’s an important one.
What the 2006 research paper shows is that 70% of web pages that compress at a level of 4.0 or higher tended to be low quality pages with a high level of redundant word usage. The average compression level of sites was around 2.0.
Here are the averages of normal web pages listed by the research paper:
- Compression ratio of 2.0:
The most frequently occurring compression ratio in the dataset is 2.0. - Compression ratio of 2.1:
Half of the pages have a compression ratio below 2.1, and half have a compression ratio above it. - Compression ratio of 2.11:
On average, the compression ratio of the pages analyzed is 2.11.
It would be an easy first-pass way to filter out the obvious content spam so it makes sense that they would do that to weed out heavy-handed content spam. But weeding out spam is more complicated than simple solutions. Search engines use multiple signals because it results in a higher level of accuracy.
The researchers from 2006 reported that 70% of sites with a compression level of 4.0 or higher were spam. That means that the other 30% were not spam sites. There are always outliers in statistics and that 30% of non-spam sites is why search engines tend to use more than one signal.
Do Search Engines Use Compressibility?
It’s reasonable to assume that search engines use compressibility to identify heavy handed obvious spam. But it’s also reasonable to assume that if search engines employ it they are using it together with other signals in order to increase the accuracy of the metrics. Nobody knows for certain if Google uses compressibility.
Impossible To Determine If Google’s Using Compression
This article is about the fact that there is no way to prove that a compression ratio is an SEO myth or not.
Here’s why:
1. If a site triggered the 4.0 compression ratio plus the other spam signals, what would happen is that those sites wouldn’t be in the search results.
2. If those sites are not in the search results, there is no way to test the search results to see if Google is using compression ratio as a spam signal.
It would be reasonable to assume that the sites with high 4.0 compression ratios were removed. But we don’t know that, it’s not a certainty. So we can’t prove that they were removed.
The only thing we do know is that there is this research paper out there that’s authored by distinguished scientists.
Compressibility Is Not Something To Worry About
Compressibility may or may not be an SEO myth. But one thing is fairly certain: it’s not something that publishers or SEOs who publish normal sites should worry about. For example, Google canonicalizes duplicate pages and consolidates the PageRank signals to the canonicalized page. That’s entirely normal with dynamic websites like ecommerce web pages. Product pages may also compress at a higher rate because there might not be a lot of content on them. That’s okay, too. Google is able to rank those.
Something like compression takes abnormal levels of heavy-handed spam tactics to trigger them. Then consider that spam signals are not used in isolation because of false positives, it’s probably not unreasonable to say that the average website does not have to worry about compression ratios.
Featured Image by Shutterstock/Roman Samborskyi
