I saw an article referenced on the Wall Street Journal's webpage and found the analysis to be interesting (but that may be because I am a dork). Basically, they use the frequency each columnist uses specific, unique words and then apply that to individual columns to see if they can determine the author of the different columns.
I think the most interesting part was the list of the top words and adjectives/adverbs used by each author.
Sad news. I admit I've only read I Am Legend (or rather, heard it on audio book), but Matheson was prolific. Here's a 2011 story on why Hollywood loved his works as source material for movies. (theatlantic.com)