I haven't read the full PDF, but the below diagram gives a breakdown, and since it is a diagram from Forrester, it is now also a fact:

I've always thought infosec people had the nicest bums. Especially if you compare them to network monkey or coder bums, which are usually flabby. Now we have proof!

I did think Yusuf's take via IRC was rather funny:

<cynic> I get the feeling that Forrester, Gartner et al are making it up sometimes.
<cynic> "Heat level" for roles in IT? What is this, TheStyleNetwork? Next we'll be seeing a report that ranks "Most Bodacious Management Skillz" ... sheesh!
<cynic> Moral Of The Story: It doesn't become less stupid if you attach a graph to it.