“[A] seven-person team of statisticians, machine-learning experts and computer engineers …. was the longtime frontrunner in the contest…. The Netflix contest has been widely followed because its lessons could extend well beyond improving movie picks.”  – Steve Lohr, “Netflix Awards $1 Million Prize and Starts a New Contest,” New York Times, September 21, 2009

Finally…!  Someone who knows how to use a hyphen!  Lohr hyphenates “seven-person ” and “machine-learning” because these two-word phrases come before the nouns they describe – “team” and “experts.” There’d be no hyphen if either two-word phrase came afterthe noun: “They were experts in machine learning.” 

For more tips on how to use hyphens correctly, see Write It Well’s book Professional Writing Skills: A Self-Paced Training Program.