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As Frederico says, Open Site Explorer uses the Mozscape link index which only crawls a portion of the internet. On the front page of Open Site Explorer you'll see some stats about the index: 106 Billion URLs, 150 Million Root domains, 764 Billion Links. While this sounds like a lot - it's nowhere near every link and every domain on the internet! I believe Raven uses MajecticSEO's link index which may (or may not) index the sites that link to your site hence the disparity between the two.

Hi, many thanks for your response. Yes I am sure I selected the exact match option before. However, is there away to select Borad Match in the new Keyword Planner to see if this displays similar levels of traffic to that I received earlier, in order to double check.

I'm using this toolhttp://www.seocentro.com/tools/search-engines/pagerank.html