Second, I find questionable the authors' conclusion that negative evaluations cause the subsequent decline in post quality and increase in post frequency, since they did not control the positive/negative evaluations. They model the positive/negative evaluations as random acts of chance
If a community really votes as random acts of chance, that explains that the voting doesn't lead to good behavior ;)
This article discusses how upvotes and downvotes influence the quality of posts on online communities. The article claims that downvotes lead to more posts of lower quality from the downvoted commenter.
From the abstract:
Social media systems rely on user feedback and rating mechanisms for personalization, ranking, and content filtering. [...] This paper investigates how ratings on a piece of content affect its author’s future behavior. [...] [W]e find that negative feedback leads to significant behavioral changes that are detrimental to the community. Not only do authors of negatively-evaluated content contribute more, but also their future posts are of lower quality, and are perceived by the community as such. In contrast, positive feedback does not carry similar effects, and neither encourages rewarded authors to write more, nor improves the quality of their posts.
The authors of the article are Justin Cheng, Cristian Danescu-Niculescu-Mizil, and Jure Leskovec.
Edited to add: NancyLebovitz already posted about this study in the Open Thread from September 8-14, 2014.