"What this means is that while just as many productive contributors enter the project today as in 2006, they are entering an environment that is increasingly challenging, critical, and/or hostile to their work. These latter findings have also been confirmed through previous research."

This confirms to me what I argued on HN last year: http://news.ycombinator.com/item?id=3272926 and http://news.ycombinator.com/item?id=3273204