Reader Paul Berg wrote some weeks back to complain about a TV ad for a stop-smoking drug called Chantix. "During the commercial, the voice-over announcer proclaims: '40% of Chantix users were quit after 20 weeks' -- or words to that effect," he wrote. "'Were quit'? This drives me nuts!"
I'd never seen the commercial, but I dug one up, and the actual voiceover says, "44 percent of Chantix users were quit during weeks 9 to 12 of treatment, compared to 18 percent on sugar pill." Not normal English, I agree. Not because "were quit" is incorrect -- you'll run across it often in Brit lit -- but the idiom is 'be quit of [i.e., finished with] something." The OED's examples span the years from c. 1200 to 1997, and include one from Jane Austen: "They ... seemed to think it as great an escape to be quit of the intrusion of Charles Maddox."
But "be quit of" doesn't work when the subject is smoking (unless you want to say, "At last I am quit of that nasty habit"). So why use it? Well, "44 percent had quit" would suggest to many listeners that those smokers had quit forever, not just stopped for weeks 9 to 12 -- something very unlikely to be true. "Forty-four percent were not smoking" would be standard English, but it lacks the victorious ring of "were quit." I don't know if "were quit" is researchers' jargon or just marketers' bafflegab, but I strongly suspect that it's meant to gloss over the question of how many people on Chantix "stayed quit" in weeks 13 and up.