Marketers are increasingly creating more content but are receiving less engagement from consumers with each piece, according to a recent report from TrackMaven.

The report was based on an analysis of the content pieces posted by 22,957 brands between January and December 2015 on blogs and five major social networks (Facebook, Twitter, Instagram, Pinterest, and LinkedIn). The sample included 75.7 billion interactions across 50 million pieces of brand-generated content.

The output of content per brand, per channel, increased 35% from its highest to lowest points last year, the analysis found. However, engagement with branded content fell, on average, 17% in 2015, to 2.19 interactions per post, per brand, per 1,000 followers.

In other words, as marketers ramped up content production through the year, they began to receive less engagement per piece of content.

Below, additional key findings from the report.

Engagement by Social Channel

Facebook had the highest average engagement ratio per post per 1,000 followers in 2015.

Average engagement per post dropped 49% on Pinterest from the beginning of 2015 to the end.