SAN FRANCISCO: Adjustments to Facebook's algorithm have had an adverse impact on the reach of publishers' posts, new data has claimed.

According to SocialFlow, a social media optimisation business, stories posted to the platform in May reached an average of 68,000 users, down from 117,000 in January. The figures come from SocialFlow's own customer base.

"Facebook is constantly adjusting its algorithms up and down to tune the user experience," said Jim Anderson, SocialFlow chief executive.

"Back in the fourth quarter and through January, media companies were doing phenomenally well," he told the Financial Times. "Then Facebook made a change to the algorithm.

"These algorithms are pretty complicated," he added. "I'm not sure even Facebook engineers know their impact, they just have to measure and respond."

His own company's measurements indicated that, in addition to reaching 42% fewer people with each story, the total combined reach of all Facebook posts was down 12%, from 42bn to 37bn over the same period; the difference is explained by the total number of posts rising at the same time.

While Facebook declined to provide an explanation, Anderson speculated that the social networking site could have prioritised posts from individuals in order to reward them for sharing more personal stories.

Or it could have been trying to ensure people's feeds didn't feature several articles from the same news organisation consecutively. A third possibility could be that it was seeking to prioritise video content.

A separate study from analytics firm NewsWhip has also noted a 44% decline in engagement with publishers' posts.

MediaPost reported that the combined activity for the ten biggest English-language publishers on Facebook fell from 287m engagements per month in July 2015 to 162m in April 2016 and ventured that the platform might be gearing up to get publishers to pay to achieve wider reach.

Data sourced from Financial Times, MediaPost; additional content by Warc staff