A recent study by Wildfire Interactive looked at 10,000 randomly sampled Facebook campaigns to see which got the highest response rates and earned media. Among the findings were a lack of correlation between the two. The campaigns that got the most earned media were not the ones that got the highest response rates.
If you’re looking for the latter, then coupons, giveaways and sweepstakes are the way to go. If you want people to share your posts, though, then try “pick your favorites” queries, quizzes and trivia contests.
The report speculated about why such campaigns tend to be more shareable. One possibility is that questions let the user discover an aspect of her personality she was unaware of. Another is the show-off factor: Quizzes let users display their knowledge of trivia, and “pick your favorites” challenges let them flout their good taste.