Marketers have suspected for some time that organic Facebook post reach is on the decline. Last year, Facebook released an algorithm update with the stated goal of weeding out spammy content. At the time, the social network reassured business users that median page reach would not change. But after the change some brands claimed that their unpaid (organic) posts were appearing in fewer fans' News Feeds. Companies were understandably concerned about their continued ability to reach consumers.

Shortly after the...