One important subtlety is that the observed proportion of
up-votes is not entirely a direct consequence of the actual
textual quality of the post, but could also be due to a community’s
biased perception of a user. In particular, the drop
in the proportion of up-votes received by users after negative
evaluations observed in Figure 2 could be explained by
two non-mutually exclusive phenomena: (1) after negative
evaluations, the user writes posts that are of lower quality
than before (textual quality), or (2) users that are known to
produce low quality posts automatically receive lower evaluations
in the future, regardless of the actual textual quality
of the post (community bias).