The NBA provides an intriguing place to test for taste-based discrimination: referees and players are involved in repeated interactions in a high-pressure setting with referees making the type of split-second decisions that might allow implicit racial biases to manifest themselves. Moreover, the referees receive constant monitoring and feedback on their performance. (Commissioner Stern has claimed that NBA referees "are the most ranked, rated, reviewed, statistically analyzed and mentored group of employees of any company in any place in the world.") The essentially arbitrary assignment of refereeing crews to basketball games, and the number of repeated interactions allow us to convincingly test for own-race preferences. We find --even conditioning on player and referee fixed effects (and specific game fixed effects) --that more personal fouls are called against players when they are officiated by an opposite-race refereeing crew than when officiated by an own-race crew. These biases are sufficiently large that we find appreciable differences in whether predominantly black teams are more likely to win or lose, based on the racial composition of the refereeing crew.

How Uber affects public transit ridership is a relevant policy question facing cities worldwide. Theoretically, Uber's effect on transit is ambiguous: while Uber is an alternative mode of travel, it can also increase the reach and flexibility of transit's fixed-route, fixed-schedule service. We use a difference-indifferences design to measure the effect of Uber on public transit ridership. The design exploits variation across U.S. metropolitan areas in both the intensity of Uber penetration (as measured using data from Google Trends) and the timing of Uber entry. We find that Uber is a complement for the average transit agency. This average effect masks considerable heterogeneity, with Uber being more of a complement in larger cities and for smaller transit agencies. Comparing the effect across modes, we find that Uber's impact on bus ridership follows the same pattern as for total ridership, though for rail ridership, it is a complement for larger agencies.

a b s t r a c tUsing data from the American Time Use Survey, I find that a first-born child receives 20-30 more minutes of quality time each day with his or her parent than a second-born child of the same age from a similar family. The birth-order difference results from parents giving roughly equal time to each child at any point in time while the amount of parent-child quality time decreases as children get older. These results provide a plausible explanation for recent research showing a very significant effect of birth order on child outcomes.

The elaborate songs of songbirds are frequent models for investigating the evolution of animal signals. However, few previous studies have attempted to reconstruct historical changes in song evolution using a phylogenetic comparative approach. In particular, no comparative studies of bird song have used a large number of vocal characters and a well-supported, independently derived phylogeny. We identified 32 features in the complex vocal displays of male oropendolas (genera Psarocolius, Gymnostinops, and Ocyalus) that are relatively invariant within taxa and mapped these characters onto a robust molecular phylogeny of the group. Our analysis revealed that many aspects of oropendola song are surprisingly evolutionarily conservative and thus are potentially useful characters for reconstructing historical patterns. Of the characters that varied among taxa, nearly two thirds (19 of 29) showed no evidence of evolutionary convergence or reversal when mapped onto the tree, which was reflected in a high overall consistency index (CI = 0.78) and retention index (RI = 0.88). Some reconstructed patterns provided evidence of selection on these signals. For example, rapid divergence of the songs of the Montezuma oropendola, Gymnostinops montezuma, from those of closely related taxa suggests the recent influence of strong sexual selection. In general, our results provide insights into the mode of vocal evolution in songbirds and suggest that complex vocalizations can provide information about phylogeny. Based on this evidence, we use song characters to estimate the phylogenetic affinities of three oropendola taxa for which molecular data are not yet available.

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We use data from the General Social Survey (GSS) over a 40-year period (1973-2012) to evaluate changes in attitudes about pornography and pornography consumption among American young adults. One of the major challenges in making comparisons across birth generations is separating the effect of birth cohort from age and period effects. We use an intrinsic estimator to separately identify the effects of age, birth cohort, and time period using 40 years of repeated cross-section data. We find that, relative to the general population, young people's beliefs about whether pornography should be illegal have stayed relatively constant over this 40-year period and, if anything, have slightly increased. We also find that pornography consumption has been increasing across birth generations, though this increase has been smaller than would be inferred based on differences across generations at a single point in time, due to a strong age component in consumption patterns.

Using data from the American Time Use Survey, I find that a first-born child receives 20-30 more minutes of quality time each day with his or her parent than a second-born child of the same age from a similar family. The birth-order difference results from parents giving roughly equal time to each child at any point in time while the amount of parent-child quality time decreases as children get older. These results provide a plausible explanation for recent research showing a very significant effect of birth order on child outcomes.