A few days ago, I read a post on one of those SEO boards asking about how to hide that you are using SSI by using a .htaccess file. The poster was convinced that .shtml files would rank lower than .html files, so they wanted to create .html files, but still have them parsed for SSI.
I've seen similar posts where people are trying to hide that they are using PHP or ASP for their sites. Somehow, they are convinced that pages ending in .html are going to rank higher than pages ending in something else. Are they right? No! In fact, .html is the worst extension you can have for ranking well on the leading search engine.
Let's get into how we did the study. I gathered the results of the queries I naturally performed last month using the leading search engine and analyzed the URLs of the results. The endings were sorted and tabulated for the first 10 rankings and converted into a normalized "ranking correlation."
The resulting number shows each stem extension normalized to a number between -100 and +100 showing the likelihood of being ranked higher/lower. A value of +100 shows that all 10 rankings were in the proper order to show that pages of the studied size ALWAYS rank HIGHER than pages of another size. A value of -100 shows that all 10 rankings were in the proper order to show that pages of the studied size ALWAYS rank LOWER than pages of another size. Numbers in between show the varying likelihood of rankings proportionally between -100 and +100. That is the number you see on the Y-axis.
On the X-axis, we have various stem extensions. I found many other extensions, but I didn't have a sufficient sample size to accurately calculate a ranking correlation. Here is the graph: http://www.SearchEngineGeek.com/graphs/dag01.jpg
The far right attribute on the X-axis shows results that had no stem whatsoever (otherwise known as home pages). I included it to show why all of the other bars are in the negative. The leading search engine really prefers home pages to any sub-pages!
The attribute just left of that shows pages that had a stem, but didn't have an ending at all. They were subdirectories that ended in a slash. Although the result is negative, this turns out to be the very best page extension for ranking in this study.
So; what happened to our .html pages? Yep; that's right. They turn out to be the very worst! Trying to disguise PHP, ASP or SSI (shtml) pages as .html pages turns out to be a very, very counter-productive exercise. Once again, the popular belief is shown to be completely inaccurate with this study.
Notes:
1. Over 1,000 queries were examined for this study.
2. There was no exercise to attempt to isolate different keywords. I merely took a random sampling of the queries I performed during the month.
Conclusion:
Sub-pages ending in a slash rank higher than any stem extension on the leading search engine! Sub-pages ending in .html and .htm tie for ranking the lowest of any page extension studied!
This is merely a correlation study, so it cannot be determined from this study whether the leading search engine purposefully entertains this factor or not. The actual factors used may be far distant from the factor we studied, but the end result is that this search engine does, in fact, rank sub-pages ending in a slash higher than sub-pages ending in .html, .htm, .php, .asp or .shtml.