How do you know how many direct "type ins" for a keyword or search term?

I having been checking out many keywords and search terms. They will display the Global search and local, how do you know how many people try to type that directly instead of going to search engine? Is it just basically a guess considering the number of searches performed? Say 1 million global searches it must have at least 1000 type-ins. I am just curious as to where some numbers I see posted come from.

Thanks domainers, Nick