Manipulation-Robust Regression Discontinuity Designs

In regression discontinuity designs, manipulation threatens identification. A known channel of harmful manipulations is precise control over the observed assignment, but this channel is only an example. This study uncovers the only other channel: sample selection by deciding manipulation precisely based on the given assignment status. For example, in the assignment design of a qualification exam, self-selection by allowing test retakes precisely based on failing the exam is a precise decision. This precise decision harms identification without precisely controlling the final assignment. For instance, retaking the test never ensures passage, but it distorts the qualification assignment because some students that failed then pass. However, students that have already passed, never fail. This novel channel redefines the justification for identification. Furthermore, under a new auxiliary condition, McCrary (2008)'s test is able to confirm identification and the existing worst-case bounds are nested within our new bounds. In a replication study, another sample selection by analysts appears critical in the robustness of their original conclusion.Comment: This work has been circulated as "Harmless and Detectable Manipulations of the Running Variable in Regression Discontinuity Designs: Tests and Bounds.

Joint diagnostic test of regression discontinuity designs: multiple testing problem

Current diagnostic tests for regression discontinuity (RD) design face a multiple testing problem. We find a massive over-rejection of the identifying restriction among empirical RD studies published in top-five economics journals. Each test achieves a nominal size of 5%; however, the median number of tests per study is 12. Consequently, more than one-third of studies reject at least one of these tests and their diagnostic procedures are invalid for justifying the identifying assumption. We offer a joint testing procedure to resolve the multiple testing problem. Our procedure is based on a new joint asymptotic normality of local linear estimates and local polynomial density estimates. In simulation studies, our joint testing procedures outperform the Bonferroni correction

EFFECTS OF TAI CHI EXERCIE ON ATTENTION IN HEALTHY ELDERLY SUBJECTS AS MEASURED BY NEAR-INFRARED SPECTROSCOPY DURING THE STROOP TASK

Background: To our knowledge，there is no study that has examined the effect of Tai Chi exercise(Tai Chi) on attention function using functional brain imaging methodologies. Recent developments in near-infrared spectroscopy(NIRS) have enabled non-invasive clarification of brain functions by measurement of hemoglobin concentrations as cerebral blood volume. So, in the present study, we examined the effects of Tai Chi in the healthy elderly as measured by NIRS during the Stroop task. Methods: Twelve healthy elderly subjects participated in the present study after giving consent. The relative concentrations of oxyhemoglobin(oxy-Hb) were measured with frontal probes every 0.1 sec during the Stroop color-word task, using 24-channel NIRS machines. Results: The Stroop task scores after the Tai Chi term were significantly higher than those before the Tai Chi term. There were no significant differences in the mean oxy-Hb changes between the conditions before and after Tai Chi. Conclusions: Our study suggested that Tai Chi promoted attention function in healthy elderly subjects, and maintained oxy-Hb concentration changes in healthy elderly subjects

EFFECTS OF TAI CHI EXERCISE ON THE HEALTHY ELDERLY AS MEASURED BY EVENT-RELATED POTENTIALS

Aim: Tai Chi exercise could be recommended as a mental training method to ameliorate cognitive function, especially attention function. Event-related potentials(ERPs) are commonly used as physiological measures of cognitive function as they are easily measured and nor-invasive. However, to our knowledge, there is no report to indicate Tai Chi's effect on cognitive function using ERPs. Therefore, in the present study we examined the effects of Tai Chi exercise on the healthy elderly as measured by ERPs. Methods: Eight healthy elderly subjects participated after giving consent. Based on the guidelines for evoked potential measurement, mismatch negativity(MMN) and P300 were obtained by auditory odd-ball tasks. We measured both MMN and P300 in the conditions before and after the Tai Chi term. Results: The MMN amplitudes after the Tai Chi term tend to be greater than those before the Tai Chi term at Fz and Cz. The P300 latency after the Tai Chi term was significantly shorter than that before the Tai Chi term at Pz. Conclusion: MMN and P300 might be sensitive tools for measuring the effects of Tai Chi exercise on the healthy elderly

The Impact of a Supernova Explosion in a Very Massive Binary

We consider the effect of a supernova (SN) explosion in a very massive binary that is expected to form in a portion of Population III stars with the mass higher than 100$M_\odot$. In a Population III binary system, a more massive star can result in the formation of a BH and a surrounding accretion disc. Such BH accretion could be a significant source of the cosmic reionization in the early universe. However, a less massive companion star evolves belatedly and eventually undergoes a SN explosion, so that the accretion disc around a BH might be blown off in a lifetime of companion star. In this paper, we explore the dynamical impact of a SN explosion on an accretion disc around a massive BH, and elucidate whether the BH accretion disc is totally demolished or not. For the purpose, we perform three-dimensional hydrodynamic simulations of a very massive binary system, where we assume a BH of $10^3 M_{\odot}$ that results from a direct collapse of a very massive star and a companion star of $100 M_{\odot}$ that undergoes a SN explosion. We calculate the remaining mass of a BH accretion disc as a function of time. As a result, it is found that a significant portion of gas disc can survive through three-dimensional geometrical effects even after the SN explosion of a companion star. Even if the SN explosion energy is higher by two orders of magnitude than the binding energy of gas disc, about a half of disc can be left over. The results imply that the Population III BH accretion disc can be a long-lived luminous source, and therefore could be an important ionizing source in the early universe.Comment: 12 pages, 9 figures, accepted for publication in MNRAS, for high resolution figures, see http://www.rccp.tsukuba.ac.jp/Astro/Members/junichi/sus2008.pd

Resolved Measurements of X_(CO) in NGC 6946

We present the largest sample to date of giant molecular clouds (GMCs) in a substantial spiral galaxy other than the Milky Way. We map the distribution of molecular gas with high resolution and image fidelity within the central 5 kpc of the spiral galaxy NGC 6946 in the ^(12)CO (J = 1-0) transition. By combining observations from the Nobeyama Radio Observatory 45 m single dish telescope and the Combined Array for Research in Millimeter Astronomy interferometer, we are able to obtain high image fidelity and accurate measurements of L_CO compared with previous purely interferometric studies. We resolve individual GMCs, measure their luminosities and virial masses, and derive X CO—the conversion factor from CO measurements to H2 masses—within individual clouds. On average, we find that X_CO = 1.2 × 10^(20) cm^(–2) (K km s^(–1))^(–1), which is consistent within our uncertainties with previously derived Galactic values as well as the value we derive for Galactic GMCs above our mass sensitivity limit. The properties of our GMCs are largely consistent with the trends observed for molecular clouds detected in the Milky Way disk, with the exception of six clouds detected within ~400 pc of the center of NGC 6946, which exhibit larger velocity dispersions for a given size and luminosity, as has also been observed at the Galactic center