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Google AdWords Broad Match Explained
7/16/2009
As most junior search marketers, knows Google's Broad Match is quite liberal in matching your keywords to search queries. Indeed, this is the intent of the match type, but sometimes it gets pretty crazy. Recently I had a scenario come up where the search queries that were mapping to the keywords did not seem logical. It was something like this:
Search query: car dealer sale
Keyword 1: car sale
Keyword 2: auto sale
Both keyword 1 and keyword 2 were on broad match. Logically, you would think the search query should map to keyword 1 because it has more words in common (2 out of 3 instead of 1 out of 3). I had a chat some folks in the know, and we got into something called "match length" - basically, a scoring system that Google uses to choose which of your own keywords will "win" to enter the SERP auction. We also got into how Google looks at the semantics of the keywords, and how that plays into match length. With the example, one would logically think keyword 1 would get +100 points (hypothetical) for car, and +100 for sale. In turn, Keyword 2 would only get 100 points, because it has only one word which actually matches. Points are assigned for other characteristics as well (see bad MS Paint illustration below)
In actuality, keyword 2 got selected over keyword 1. This is because the unique keywords were viewed as the exact same things. This has to do with how Google's system "re-writes" keywords. Google re-wrote the word "auto" to "car" because the intent is so similar (they call them "related words"). Google verifies these re-writes internally by looking at the CTRs of the re-writes, and if the CTR is bad, it eventually verifies a bad re-write. Other ways Google re-writes are spell correction, and so called "query broadening." Thus, each of the keywords appeared as if they were the same. So keyword 2 was selected due to factors other than the words themselves (geo-targeting, bid, quality score). In this case, keyword 2 was chosen because it had a higher ad rank (and ad rank is your quality score times your bid).
Some other details of how the paid search algorithms work were divulged to me. Some of them were pretty "duh," such as the fact that exact match will always trump phrase and broad match, and other fairly common-sense nuggets. Exact match will always, always win, regardless of ad rank, quality score, or bid. So, if you bid your exact keywords down to a nickel, beware! However, a keyword in campaign that is more geo-targeted than another will get more "points" when considering which of your keywords to choose. If someone is sitting in Memphis, TN, and they perform a search with a query that could potentially map to multiple keywords in your account (all other things being equal), the likelihood of the keyword in a campaign geo-targeted to Memphis is greater a keyword in a nationally targeted campaign. I assume all of this was put into layman's terms so that a search marketer such as myself can understand the basics of the algorithm, but you get the gist of things.
Google makes it very difficult to have precise control with Broad match. The best way to mitigate for the "efficiencies" Google creates is with many ad groups and proper negative keywords to ensure cross -coverage. This can become cumbersome quickly, however, so pick and choose your battles wisely!
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