Explaining Google's algorithm
Friday, 30 May 2008
By Chris Thomas
Perhaps the eighth wonder of the world should be Google’s mysterious “algorithm”. By the way, I do say that with tongue planted firmly in cheek (never really understood that turn of phrase, if any one can tell its origins that’d be great).
But I do regularly get asked about it. What is it? What’s in it? What does it do?
Today, I’ll take a bit of a stab at what it is and what we know about it.
I think I mentioned many-a-blog-post-ago that there are three parts to a search engine; the robots, the index and the algorithm. I’ll do a very simple re-cap to put it into context.
Remember, the “bots” go out over the internet and find and collect web pages. When they find a page, they scurry back and plonk it into Google’s massive storage system, the index.
The third part of the “engine” is the algorithm, which effectively analyses each page for relevance. When someone performs a search, it tries its best to sort all pages in the index, ranking the most relevant result highest, then the second most relevant page... well, second, and the third and so on.
The problem for you and I is that Google doesn’t tell us exactly how the algorithm works. It can’t really, because for starters, if Google did “give it all away” competitors would no-doubt copy it, and there’d be an optimisation free-for-all by every website owner out there.
It’s Google’s own “11 secret herbs and spices” recipe.
I read recently that in 2007 Google changed or tweaked the algorithm around 450 times. That’s more than once a day! Talk about a moving target! That’s the main reason we will never guarantee a number one position at Google. Customer expectation management 101.
I think the most important thing to remember about the algorithm is that while it’s been written and updated by humans, there is no human involvement in a website’s ranking position.
It’s best summed up by Ubi Manber, Google vice president who oversees search quality. "If we find, for a particular query, that result No. 4 should be result No. 1, we do not have the capability to manually change it. We have to find what weakness in the algorithm caused that result and find a general solution to that, evaluate whether a general solution really works and if it's better, and then launch a general solution."
While Google might be constantly fiddling around the edges, there are things about the algorithm which tend to remain fairly constant. Over at SeoMoz (effectively the SEO industry’s version of SmartCompany), the world’s top SEO industry experts were invited to vote on what they believed were most important factors to influence Google’s algorithm.
The title tag came in first, followed by body text and headings etc. Certainly, links are also a play a huge factor, and the anchor text of in-bound-links to a site was of “exceptional importance” to all respondents.
Even so, the algorithm doesn’t always get it spot on. The main inspiration for this post was the research I was doing to the AIMIA speech last week, “the future of search”. When I typed that key phrase into Google for some inspiration, the number 1 result’s content was written in 2004.
So, there’s still some work left for Google to do!
Read more on search engine rankings
Chris Thomas heads Reseo a search engine optimisation company which specialises in setting up and maintaining Google AdWords campaigns, Affiliate Programs and Search Engine Optimisation campaigns for a range of corporate clients.
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Comments
Matt writes: I recall one of the Google guys talking about their initial premise. Sure the algorithm looks at content, but the thing that made Google different was it looked at how many references there were to that page. If people put the time and effort into linking to a page, then it must be pretty relevant. They likened it to the academic referencing principles. Many theses will reference a reputable source. I wouldn't be surprised that another part is user provided. That is, the search results provide an abstract. From that a user will determine whether the article is relevant. Therefore, the more users who select a result the more relevant it must be. It's not rocket science :)
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