Economists have become increasingly interested in studying the nature of production functions in social policy applications, with the goal of improving productivity. Traditionally models have assumed workers are homogenous inputs. However, in practice, substantial variability in productivity means the marginal productivity of labor depends substantially on which new workers are hired--which requires not an estimate of a causal effect, but rather a prediction. We demonstrate that there can be large social welfare gains from using machine learning tools to predict worker productivity, using data from two important applications - police hiring and teacher tenure decisions.

We investigate whether Facebook users have become more private in recent years. Specifically, we examine if there have been any important trends in the information Facebook users reveal about themselves on their public profile pages since early 2010. To this end, we have crawled the public profile pages of 1.4 million New York City (NYC) Facebook users in March 2010 and again in June 2011.We have found that NYC users in our sample have become dramatically more private during this period. For example, in March 2010 only 17.2% of users in our sample hid their friend lists, whereas in June 2011, just 15 months later, 52.6% of the users hid their friend lists. We explore privacy trends for several personal attributes including friend list, networks, relationship, high school name and graduation year, gender, and hometown. We find that privacy trends have become more pronounced for certain demographics. Finally, we attempt to determine the primary causes behind the dramatic decrease in the amount of information Facebook users reveal about themselves to the general public.

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