Knowledge that Transforms

This study makes use of detailed student-level data from eight cohorts of first-year students at Northwestern University to investigate the relative effects of tenure track/tenured versus contingent faculty on student learning. We focus on classes taken during a student’s first term at Northwestern and employ an identification strategy in which we control for both student-level fixed effects and next-class-taken fixed effects to measure the degree to which contingent faculty contribute more or less to lasting student learning than do other faculty. We find consistent evidence that students learn relatively more from contingent faculty in their firstterm courses. This result is driven by the fact that the bottom quarter of tenure track/tenured faculty (as indicted by our measure of teaching effectiveness) has lower “value added” than their contingent counterparts. Differences between contingent and tenure track/tenured faculty are present across a wide variety of subject areas and are particularly pronounced for Northwestern’s averages and less-qualified students.

We use georeferenced information on the location of violent events in sub-Saharan African countries and provide evidence that external income shocks are important determinants of the intensity and geography of civil conflicts. More precisely, we find that (a) the incidence, intensity, and onset of conflicts are generally negatively and significantly correlated with income variations at the local level; (b) this relationship is significantly weaker for the most remote locations; and (c) at the country level, these shocks have an insignificant impact on the overall probability of conflict outbreak but do affect the probability that conflicts start in the most opened regions.

We use unique longitudinal data to document an economically and statistically significant positive correlation between the facial attractiveness of male high school graduates and their subsequent labor market earnings. There are only weak links between facial attractiveness and direct measures of cognitive skills and no link between facial attractiveness and mortality. Even after including a lengthy set of characteristics, including IQ, high school activities, proxy measures for confidence and personality, family background, and additional respondent characteristics in an empirical model of earnings, the attractiveness premium is present in the respondents' mid-30s and early 50s. Our findings are consistent with attractiveness being an enduring, positive labor market characteristic.

We exploit daylight saving time (DST) as an exogenous shock to daylight, using both the discontinuous nature of the policy and the 2007 extension of DST, to consider the impact of light on criminal activity. Regression discontinuity estimates show a 7% decrease in robberies following the shift to DST. As expected, effects are largest during the hours directly affected by the shift in daylight. We discuss our findings within the context of criminal decision making and labor supply, and estimate that the 2007 DST extension resulted in $59 million in annual social cost savings from avoided robberies.

Governments around the world are reforming their social security systems in light of the challenges posed by population aging. We study the 1993 Australian Age Pension reform, which progressively increased the eligibility age for women from 60 to 65 years. We find economically significant responses to the reform. An increase in the eligibility age of one year induced a decline in the probability of retirement by 12 to 19 percentage points. In addition, the reform induced significant program substitution, with increases in enrollment in other social insurance programs, particularly the disability support pension, which effectively functioned as an alternative source of retirement income.

We model spatial clusters of similar firms. Our model highlights how agglomerative forces lead to localized, individual connections among firms, while interaction costs generate a defined distance over which attraction forces operate. Overlapping firm interactions yield agglomeration clusters that are much larger than the underlying agglomerative forces themselves. Empirically, we demonstrate that our model’s assumptions are present in the structure of technology and labor flows within Silicon Valley. Our model further identifies how the lengths over which agglomerative forces operate influence the shapes and sizes of industrial clusters; we confirm these predictions using variations across patent technology clusters.

We show that very large firms shape country export patterns. Among 32 countries, the top firm on average accounts for 14% of a country’s total (nonoil) exports, and the top five firms make up 30%. These export superstars are also important in the sectoral distribution of exports. Variation in exports from the top firm in a country explains about one-third of the variation in sectoral exports relative to income across countries, and variation in exports from the top five firms explains nearly half. Revealed comparative advantage in a sector can be created by a single firm.

We draw on macroeconomic models of diffusion and productivity to explain empirical patterns of survival gains in heart attacks. Using Medicare data for 2.8 million patients during 1986-2004, we find that hospitals rapidly adopting cost-effective innovations such as beta blockers, aspirin, and reperfusion, had substantially better outcomes for their patients. Holding technology adoption constant, the marginal returns to spending were relatively modest. Hospitals increasing the pace of technology diffusion ("tigers") experienced triple the survival gains compared to those with diminished rates ("tortoises"). In sum, small differences in the propensity to adopt effective technology lead to wide productivity differences across hospitals.

Suppose that all people in the world are allocated only two characteristics over which they have (almost) no control: country of residence and income distribution within that country. Assume further that there is no migration. We show that more than one-half of variability in income of world population classified according to their household per capita in 1% income groups (by country) is accounted for by these two characteristics. The role of effort or luck cannot play a large role in explaining the global distribution of individual income.

Quantitative estimates of the impacts of climate change on economic outcomes are important for public policy. We show that the vast majority of estimates fail to account for well-established uncertainty in future temperature and rainfall changes, leading to potentially misleading projections. We reexamine seven well-cited studies and show that accounting for climate uncertainty leads to a much larger range of projected climate impacts and a greater likelihood of worst-case outcomes, an important policy parameter. Incorporating climate uncertainty into future economic impact assessments will be critical for providing the best possible information on potential impacts.