In the beginning, GTrends SE was intended for those who participated with TDC 2007. So I didn’t describe the algorithm here, as TDC’ers would already be familiar with it. However, now I’ve gotten some inquiries from new users as to how, exactly, is the number in the “Searches” column calculated. So here’s the algorithm, in short.
The search volume is calculated by comparing it to the reference keyword (Settings -> Criteria -> Reference keyword). The program sends a query with both keywords to Google Trends and calculates the searches based on the ratio of the reference/unknown keyword bar graphs. The keyword phrase that needs to be checked is wrapped in “quotes”.
The equation is something like this :
keyword_searches = ( keyword_bar_size / reference_bar_size ) * reference_searches
Pretty simple, right?
There’s one curious implication this algorithm has – for keywords that have very small search volume, it will always report the exact same (small) number of searches. The exact figure produced depends on the reference keyword and how many searches it has.
You get those similar results because Google Trends shows 1-pixel graph bars for those keywords (keyword_bar_size = 1). Trends will even show those 1-pixel bars for keywords that don’t get any searches at all. Obviously, plugging this value (1) into the above equation, you will always get the same result.
So if you notice lots of keywords with the same small number in the “Searches”, blame Google Trends, okay? 😉