Finish It and It’s Free: An Evaluation of College Graduation Subsidies

Despite the rapid increase in the returns to higher education witnessed in the labor market over the past few decades, there has also been a marked increase in the share of individuals who dropout of college or university. To boost student persistence in higher education, several Canadian provincial governments introduced a set of reforms that were designed as subsidies for college graduation. In addition, these policies were designed to discourage internal migration following graduation. Using data from both administrative tax records as well as longitudinal surveys, I analyze the effectiveness of these policies. The main findings are that the programs had no effect on internal migration, but significantly reduced college dropout rates

An HST Search for Lyman Continuum Emission From Galaxies at z=1.1--1.4

If enough of their Lyman limit continuum escapes, star-forming galaxies could be significant contributors to the cosmic background of ionizing photons. To investigate this possibility, we obtained the first deep imaging in the far ultraviolet of eleven bright blue galaxies at intermediate redshift (z=1.1--1.4). NO Lyman continuum emission was detected. Sensitive, model-independent, upper limits of typically 2 x 10**-19 erg/sec/cm2/Ang were obtained for the ionizing flux escaping from these normal galaxies. This corresponds to lower limits on the observed ratio of 1500 to 700Ang flux of 150 up to 1000. Based on a wide range of stellar synthesis models, this suggests that less than 6%, down to less than 1%, of the available ionizing flux emitted by hot stars is escaping these galaxies. The magnitude of this spectral break at the Lyman l imit confirms that the basic premise of `Lyman break' searches for galaxies at high redshift can also be applied at intermediate redshifts. This implies that the integrated contribution of galaxies to the UV cosmic background at z around 1.2 is less than 15%, and may be less than 2%.Comment: 20 manuscript pages, which includes two tables and two figures. To be published in 1 December 2003 issue of The Astrophysical Journa

The Subcluster Wild Bootstrap for Few (Treated) Clusters

Inference based on cluster-robust standard errors or the wild cluster bootstrap is known to fail when the number of treated clusters is very small. We propose a family of new procedures called the subcluster wild bootstrap. In the case of pure treatment models, where all observations within clusters are either treated or not, the new procedures can work remarkably well. The key requirement is that all cluster sizes, regardless of treatment, should be similar. Unfortunately, the analog of this requirement is not likely to hold for difference-in-differences regressions. Our theoretical results are supported by extensive simulations and an empirical example

Decision Making with Risky, Rival Outcomes: Theory and Evidence

Little is known about how individuals make decisions when they must choose several options from a set of options when the outcomes are risky and the payoffs are rival. When researchers model these decisions, they assume people maximize their expected utility. We design an experiment in which subjects face either rival or independent payoffs. While theory predicts different behavior, subjects behave nearly identically under these payoff schemes. This suggests individuals are not maximizing expected utility. Additional treatments demonstrate that this behavior is likely driven by a heuristic used to simplify a complex math problem, rather than a preference for lotteries with the highest independent expected utilities. Our results suggest that using expected utility as peoples' objective function in these types of environments will lead to biased predictions

Randomization Inference for Differences-in-Differences with Few Treated Clusters

Inference using difference-in-differences with clustered data requires care. Previous research has shown that, when there are few treated clusters, t tests based on a cluster-robust variance estimator (CRVE) severely over-reject, different variants of the wild cluster bootstrap can over-reject or under-reject dramatically, and procedures based on randomization inference show promise. We demonstrate that randomization inference (RI) procedures based on estimated coefficients, such as the one proposed by Conley and Taber (2011), fail whenever the treated clusters are atypical. We propose an RI procedure based on t statistics which fails only when the treated clusters are atypical and few in number. We also propose a bootstrap-based alternative to randomization inference, which mitigates the discrete nature of RI P values when the number of clusters is small. Two empirical examples demonstrate that alternative procedures can yield dramatically different inferences

Wild Bootstrap Inference for Wildly Different Cluster Sizes

The cluster robust variance estimator (CRVE) relies on the number of clusters being sufficiently large. Monte Carlo evidence suggests that the 'rule of 42' is not true for unbalanced clusters. Rejection frequencies are higher for datasets with 50 clusters proportional to US state populations than with 50 balanced clusters. Using critical values based on the wild cluster bootstrap performs much better. However, this procedure fails when a small number of clusters is treated. We explain why CRVE t statistics and the wild bootstrap fail in this case, study the 'effective number' of clusters and simulate placebo laws with dummy variable regressors

Immigrant category of admission and the earnings of adults and children: how far does the apple fall?

Immigrants in many Western countries have experienced poor economic outcomes. This has led to a lack of integration of child immigrants (the 1.5 generation) and the second generation in some countries. However, in Canada, child immigrants and the second generation have on average integrated very well economically. We examine the importance of Canada’s admission classes to determine if there is an earnings benefit of the selection under the economic classes to (1) the Adult Arrival immigrants and (2) the Child Arrival immigrants (1.5 generation) once old enough to enter the labour market. We employ unique administrative data on landing records matched with subsequent income tax records that also allows for the linking of the records of Adult Arrival parents and their Child Arrival children. We find, relative to the Family Class, the Adult Arrivals in the Skilled Worker category have earnings that are 29% higher for men and 38% higher for women. These differences persist even after controlling for detailed personal characteristics such as education and language fluency at 21% for men and 27% for women. Child Arrival immigrants landing in the Skilled Worker Class have earnings advantages (as adults) over their Family Class counterparts of 17% for men and 21% for women. These Child Arrival Skilled Worker advantages remain at 9% for men and 14% for women after controlling for child characteristics, the Principal Appl

Mechanisms of increased Trichodesmium fitness under iron and phosphorus co-limitation in the present and future ocean

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 7 (2016): 12081, doi:10.1038/ncomms12081.Nitrogen fixation by cyanobacteria supplies critical bioavailable nitrogen to marine ecosystems worldwide; however, field and lab data have demonstrated it to be limited by iron, phosphorus and/or CO2. To address unknown future interactions among these factors, we grew the nitrogen-fixing cyanobacterium Trichodesmium for 1 year under Fe/P co-limitation following 7 years of both low and high CO2 selection. Fe/P co-limited cell lines demonstrated a complex cellular response including increased growth rates, broad proteome restructuring and cell size reductions relative to steady-state growth limited by either Fe or P alone. Fe/P co-limitation increased abundance of a protein containing a conserved domain previously implicated in cell size regulation, suggesting a similar role in Trichodesmium. Increased CO2 further induced nutrient-limited proteome shifts in widespread core metabolisms. Our results thus suggest that N2-fixing microbes may be significantly impacted by interactions between elevated CO2 and nutrient limitation, with broad implications for global biogeochemical cycles in the future ocean.Grant support was provided by U.S. National Science Foundation OCE 1260490 to D.A.H., E.A.W. and F.-X.F., and OCE OA 1220484 and G.B. Moore Foundation 3782 and 3934 to M.A.S

Prioritizing Conservation of Ungulate Calving Resources in Multiple-Use Landscapes

BACKGROUND: Conserving animal populations in places where human activity is increasing is an ongoing challenge in many parts of the world. We investigated how human activity interacted with maternal status and individual variation in behavior to affect reliability of spatially-explicit models intended to guide conservation of critical ungulate calving resources. We studied Rocky Mountain elk (Cervus elaphus) that occupy a region where 2900 natural gas wells have been drilled. METHODOLOGY/PRINCIPAL FINDINGS: We present novel applications of generalized additive modeling to predict maternal status based on movement, and of random-effects resource selection models to provide population and individual-based inference on the effects of maternal status and human activity. We used a 2×2 factorial design (treatment vs. control) that included elk that were either parturient or non-parturient and in areas either with or without industrial development. Generalized additive models predicted maternal status (parturiency) correctly 93% of the time based on movement. Human activity played a larger role than maternal status in shaping resource use; elk showed strong spatiotemporal patterns of selection or avoidance and marked individual variation in developed areas, but no such pattern in undeveloped areas. This difference had direct consequences for landscape-level conservation planning. When relative probability of use was calculated across the study area, there was disparity throughout 72-88% of the landscape in terms of where conservation intervention should be prioritized depending on whether models were based on behavior in developed areas or undeveloped areas. Model validation showed that models based on behavior in developed areas had poor predictive accuracy, whereas the model based on behavior in undeveloped areas had high predictive accuracy. CONCLUSIONS/SIGNIFICANCE: By directly testing for differences between developed and undeveloped areas, and by modeling resource selection in a random-effects framework that provided individual-based inference, we conclude that: 1) amplified selection or avoidance behavior and individual variation, as responses to increasing human activity, complicate conservation planning in multiple-use landscapes, and 2) resource selection behavior in places where human activity is predictable or less dynamic may provide a more reliable basis from which to prioritize conservation action

Constraining the Thermal Dust Content of Lyman-Break Galaxies in an Overdense Field at z~5

We have carried out 870 micron observations in the J1040.7-1155 field, known to host an overdensity of Lyman break galaxies at z=5.16 +/- 0.05. We do not detect any individual source at the S(870)=3.0 mJy/beam (2 sigma) level. A stack of nine spectroscopically confirmed z>5 galaxies also yields a non-detection, constraining the submillimeter flux from a typical galaxy at this redshift to S(870)<0.85 mJy, which corresponds to a mass limit M(dust)<1.2x10^8 M_sun (2 sigma). This constrains the mass of thermal dust in distant Lyman break galaxies to less than one tenth of their typical stellar mass. We see no evidence for strong submillimeter galaxies associated with the ultraviolet-selected galaxy overdensity, but cannot rule out the presence of fainter, less massive sources.Comment: 5 pages, 2 figures. MNRAS in pres