Their hypothesis was the following: that wahhabi was a dominant term used after 9/11, with its use waning over the years and being replaced by the term salafi.
By looking at Google Trends, they found that Salafi was a far more popular search term since 2005 globally, but wahhabi was about as popular a term in the United States as salafi in 2005, with the steady decline in the former since then. [Graphs]
However, wahhabi is a term that can be spelled in other ways as well – the simplest being wahabi. By looking at the Google Trends search indices for all three terms, we get a slightly different picture.
Worldwide, Salafi is a term that is more prominent than both wahabi and wahhabi combined, but wahabi appears to be increasingly in use, especially since 2009. In the US, the difference between the use of either terms is less marked.
Google Trends gives us a sense of the extent of interest in these multiple terms, by examining how often people search for them. But how often are they used in writing? Another tool by Google, the excellent Ngram viewer, lets us look at how often terms are used in all books indexed in the Google Books database.
If one compares the use of wahabi, wahhabi and salafi in all books, salafi comes out as the clear victor. However, these searches are case-sensitive. Turns out that capitalised versions of all three terms are used a lot more often in books than un-capitalised versions! And with them, the trends are completely different. A comparison of Wahabi, Wahhabi and Salafi tells us that Wahhabi is the most used term in books – and it always was. It also tells us that since 9/11, more was written about both Wahhabism and Salafism. And while slow on the start, there certainly is some evidence for how Salafi is being increasingly used in books today.