UGC. Describing much of the current research being done in this area, this chapter has
focused on the impact of UGC on behavior, the unique biases and challenges to the qual-
ity of content that these platforms face, and the design of incentives to generate sufficient
high-quality content, among other issues.
Several themes have arisen throughout the chapter. One is methodological. Much of
the frontier of this field involves finding the correct method to study a given problem. In
many cases, this means identifying strategies to pinpoint causal effects that go beyond
descriptive work and associations. There is also scope for pure prediction problems in
cases where UGC may help to predict and target a variable of interest. But it is important
to be