Review of Statistics with Stata (Updated for Version 7)

The new book by Hamilton (2002) is reviewed. Copyright 2002 by Stata Corporation.

The impact of baryons on the direct detection of dark matter

The spatial and velocity distributions of dark matter particles in the Milky Way Halo affect the signals expected to be observed in searches for dark matter. Results from direct detection experiments are often analyzed assuming a simple isothermal distribution of dark matter, the Standard Halo Model (SHM). Yet there has been skepticism regarding the validity of this simple model due to the complicated gravitational collapse and merger history of actual galaxies. In this paper we compare the SHM to the results of cosmological hydrodynamical simulations of galaxy formation to investigate whether or not the SHM is a good representation of the true WIMP distribution in the analysis of direct detection data. We examine two Milky Way-like galaxies from the MaGICC cosmological simulations (a) with dark matter only and (b) with baryonic physics included. The inclusion of baryons drives the shape of the DM halo to become more spherical and makes the velocity distribution of dark matter particles less anisotropic especially at large heliocentric velocities, thereby making the SHM a better fit. We also note that we do not find a significant disk-like rotating dark matter component in either of the two galaxy halos with baryons that we examine, suggesting that dark disks are not a generic prediction of cosmological hydrodynamical simulations. We conclude that in the Solar neighborhood, the SHM is in fact a good approximation to the true dark matter distribution in these cosmological simulations (with baryons) which are reasonable representations of the Milky Way, and hence can also be used for the purpose of dark matter direct detection calculations.Comment: Minor changes to match JCAP version. 21 pages, 9 figure

The generalizability of survey experiments

Survey experiments have become a central methodology across the social sciences. Researchers can combine experiments’ causal power with the generalizability of population-based samples. Yet, due to the expense of population-based samples, much research relies on convenience samples (e.g., students, online opt-in samples). The emergence of affordable, but non-representative online samples has reinvigorated debates about the external validity of experiments. We conduct two studies of how experimental treatment effects obtained from convenience samples compare to effects produced by population samples. In Study 1, we compare effect estimates from four different types of convenience samples and a population-based sample. In Study 2, we analyze treatment effects obtained from 20 experiments implemented on a population-based sample and Amazon’s Mechanical Turk. The results reveal considerable similarity between many treatment effects obtained from convenience and nationally representative population-based samples. While the results thus bolster confidence in the utility of convenience samples, we conclude with guidance for the use of a multitude of samples for advancing scientific knowledge

Alcohol Use and Cognition at Mid-Life: The Importance of Adjusting for Baseline Cognitive Ability and Educational Attainment

The nature of the relationship between cognition and alcohol consumption remains controversial. Studies have reported negative, positive, and nonsignificant effects of alcohol consumption on cognition. Problematic throughout the literature is that baseline cognitive ability has not been adequately controlled in previous studies, and even educational attainment is only sometimes controlled. Because such variables may be associated with both alcohol intake and later-life cognition, we hypothesize that the observed relationship between alcohol intake and cognition may change when these variables or other conditions in early life have been controlled. Methods : We examined the relationship of alcohol intake and cognition at age 53 using the Wisconsin Longitudinal Study, which has followed Wisconsin high school graduates from 1957 to 1992. Our measures include cognitive ability test scores from the freshman and junior years of high school, educational attainment, an abstract reasoning test score at age 53, alcohol intake at age 53, and other measures. Results : When no controls were used, both men and women with low levels of alcohol consumption at 53 (i.e., 0–1 drink per day) had better scores on the abstract reasoning subtest of the Wechsler Adult Intelligence Scale (WAIS-R) at age 53 than subjects who never drank or currently did not drink. However, after adjusting for adolescent-measured cognitive ability and educational attainment, men with low levels of consumption no longer had higher abstract reasoning scores than nondrinking men, but they still did have higher abstract reasoning scores than men who drank more than one drink per day. For women, adjusting for cognitive ability and educational attainment eliminated all significant effects of alcohol on cognition, and reversed the nonsignificant result that women with higher consumption had the highest cognition scores. These results demonstrate the importance of adjusting for baseline cognitive ability when attempting to study the effect of long-term alcohol use patterns on cognition, and that educational attainment cannot be considered a valid substitute for baseline cognition scores. Conclusions : Much of the apparent benefit of moderate alcohol intake on cognition in our society may well be explained by differential rates of alcohol consumption among subjects with differing baseline cognitive ability scores. Neither is there evidence that moderate alcohol intake reduces cognitive functioning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65631/1/01.ALC.0000078060.18662.C1.pd

The provision of hospital chaplaincy in the United States: a national overview

Abstract: Over the past 25 years, the Joint Commission for the Accreditation of Healthcare Organizations has changed its guidelines regarding religious/spiritual care of hospitalized patients to increase attention concerning this aspect of hospital-based care. Little empirical evidence assesses the extent to which hospitals relied on hospital chaplains as care providers during these years. This study investigates (1) the extent of chaplaincy service availability in US hospitals between 1980 and 2003; (2) the predictors of having chaplaincy services in 1993 and 2003; and (3) the change in the magnitude of these predictors between years. This study examines the presence or absence of chaplaincy or pastoral care services in hospitals using the American Hospital Association Annual Survey of Hospitals (ranging from 4,946 -6,353 hospitals) in 1980 -1985, 1992-1993, and 2002-2003. Between 54% and 64% of hospitals had chaplaincy services between 1980 and 2003, with no systematic trend over this period. In 1993 and 2003, hospital size, location, and church affiliation were central factors influencing the presence of chaplaincy services. Smaller hospitals and those in rural areas were less likely to have chaplaincy services. Church-operated hospitals were much more likely to have chaplaincy services; but between 1993 and 2003, church-operated hospitals were more likely to drop chaplaincy services than to add them. Not-for-profit hospitals were more likely than investor-owned hospitals to add chaplaincy services. Changes to Joint Commission for the Accreditation of Healthcare Organizations policies about the religious/spiritual care of hospitalized patients between 1980 and 2003 seem to have had no discernible effect on the fraction of US hospitals that had chaplaincy services. Rather, characteristics of hospitals, their surroundings, and their religious affiliations influenced whether they provided chaplaincy services to patients. were more likely to drop chaplaincy services than to add them. • Not-for-profit hospitals were more likely than investor-owned hospitals to add chaplaincy services. 62

The Shifting Salience of Skin Color for Educational Attainment

Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.Findings of an association between skin color and educational attainment have been fairly consistent among Americans born before the civil rights era, but little is known regarding the persistence of this relationship in later born cohorts. The authors ask whether the association between skin color and educational attainment has changed between black American baby boomers and millennials. The authors observe a large and statistically significant decline in the association between skin color and educational attainment between baby boomer and millennial black women, whereas the decline in this association between the two cohorts of black men is smaller and nonsignificant. Compared with baby boomers, a greater percentage of the association between skin color and educational attainment among black millennials appears to reflect educational disparities in previous generations. These results emphasize the need to conceptualize colorism as an intersectional problem and suggest caution when generalizing evidence of colorism in earlier cohorts to young adults today

Most Reported Genetic Associations with General Intelligence Are Probably False Positives

General intelligence (g) and virtually all other behavioral traits are heritable. Associations between g and specific single-nucleotide polymorphisms (SNPs) in several candidate genes involved in brain function have been reported. We sought to replicate published associations between g and 12 specific genetic variants (in the genes DTNBP1, CTSD, DRD2, ANKK1, CHRM2, SSADH, COMT, BDNF, CHRNA4, DISC1, APOE, and SNAP25) using data sets from three independent, well-characterized longitudinal studies with samples of 5,571, 1,759, and 2,441 individuals. Of 32 independent tests across all three data sets, only 1 was nominally significant. By contrast, power analyses showed that we should have expected 10 to 15 significant associations, given reasonable assumptions for genotype effect sizes. For positive controls, we confirmed accepted genetic associations for Alzheimer’s disease and body mass index, and we used SNP-based calculations of genetic relatedness to replicate previous estimates that about half of the variance in g is accounted for by common genetic variation among individuals. We conclude that the molecular genetics of psychology and social science requires approaches that go beyond the examination of candidate genes.Economic