Showing papers by "University of Chicago published in 2001"

Historical overfishing and the recent collapse of coastal ecosystems.

Abstract: Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.

A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease

Abstract: Crohn's disease is a chronic inflammatory disorder of the gastrointestinal tract, which is thought to result from the effect of environmental factors in a genetically predisposed host. A gene location in the pericentromeric region of chromosome 16, IBD1, that contributes to susceptibility to Crohn's disease has been established through multiple linkage studies, but the specific gene(s) has not been identified. NOD2, a gene that encodes a protein with homology to plant disease resistance gene products is located in the peak region of linkage on chromosome 16 (ref. 7). Here we show, by using the transmission disequilibium test and case-control analysis, that a frameshift mutation caused by a cytosine insertion, 3020insC, which is expected to encode a truncated NOD2 protein, is associated with Crohn's disease. Wild-type NOD2 activates nuclear factor NF-kappaB, making it responsive to bacterial lipopolysaccharides; however, this induction was deficient in mutant NOD2. These results implicate NOD2 in susceptibility to Crohn's disease, and suggest a link between an innate immune response to bacterial components and development of disease.

Risk as feelings.

Abstract: Virtually all current theories of choice under risk or uncertainty are cognitive and consequentialist. They assume that people assess the desirability and likelihood of possible outcomes of choice alternatives and integrate this information through some type of expectation-based calculus to arrive at a decision. The authors propose an alternative theoretical perspective, the risk-as-feelings hypothesis, that highlights the role of affect experienced at the moment of decision making. Drawing on research from clinical, physiological, and other subfields of psychology, they show that emotional reactions to risky situations often diverge from cognitive assessments of those risks. When such divergence occurs, emotional reactions often drive behavior. The risk-as-feelings hypothesis is shown to explain a wide range of phenomena that have resisted interpretation in cognitive-consequentialist terms.

Laplacian Eigenmaps and Spectral Techniques for Embedding and Clustering

Abstract: Drawing on the correspondence between the graph Laplacian, the Laplace-Beltrami operator on a manifold, and the connections to the heat equation, we propose a geometrically motivated algorithm for constructing a representation for data sampled from a low dimensional manifold embedded in a higher dimensional space. The algorithm provides a computationally efficient approach to nonlinear dimensionality reduction that has locality preserving properties and a natural connection to clustering. Several applications are considered.

Ulcerative Colitis

Abstract: developing countries. It has been proposed that this is the result of improved hygiene and sanitation, which have led to reduced exposure to enteric infections and immaturity of the immune system. In a recent systematic review of population based studies, incidence varied from 0.6 to more than 20 people per 100 000 person years in Europe and North America, compared with 0.1 to 6.3 per 100 000 person years in Asia and the Middle East. Overall, incidence appeared to be on the rise worldwide. Peak incidence occurred in the second to fourth decade of life, although a modest rise was also seen in later life. Prevalence was estimated at 5-500 people per 100 000 worldwide. No consistent difference was seen between the sexes. Smoking protects against developing ulcerative colitis. Risk is eight times higher in first degree relatives of people with the disorder compared with first degree relatives of healthy controls, although this is not completely explained by known genetic risk factors.

Multilevel Analyses of Neighbourhood Socioeconomic Context and Health Outcomes: a Critical Review

Abstract: PURPOSE—Interest in the effects of neighbourhood or local area social characteristics on health has increased in recent years, but to date the existing evidence has not been systematically reviewed. Multilevel or contextual analyses of social factors and health represent a possible reconciliation between two divergent epidemiological paradigms—individual risk factor epidemiology and an ecological approach. DATA SOURCES—Keyword searching of Index Medicus (Medline) and additional references from retrieved articles. STUDY SELECTION—All original studies of the effect of local area social characteristics on individual health outcomes, adjusted for individual socioeconomic status, published in English before 1 June 1998 and focused on populations in developed countries. DATA SYNTHESIS—The methodological challenges posed by the design and interpretation of multilevel studies of local area effects are discussed and results summarised with reference to type of health outcome. All but two of the 25 reviewed studies reported a statistically significant association between at least one measure of social environment and a health outcome (contextual effect), after adjusting for individual level socioeconomic status (compositional effect). Contextual effects were generally modest and much smaller than compositional effects. CONCLUSIONS—The evidence for modest neighbourhood effects on health is fairly consistent despite heterogeneity of study designs, substitution of local area measures for neighbourhood measures and probable measurement error. By drawing public health attention to the health risks associated with the social structure and ecology of neighbourhoods, innovative approaches to community level interventions may ensue. Keywords: socioeconomic status; local area; contextual analysis; hierarchical analysis

The Great Reversals: The Politics of Financial Development in the 20th Century

Abstract: Indicators of the development of the financial sector do not improve monotonically over time. In particular, we find that by most measures, countries were more financially developed in 1913 than in 1980 and only recently have they surpassed their 1913 levels. This pattern cannot be explained by structural theories that attribute cross-country differences in financial development to time-invariant factors, such as a country's legal origin or culture. We propose an "interest group" theory of financial development where incumbents oppose financial development because it breeds competition. The theory predicts that incumbents' opposition will be weaker when an economy allows both cross-border trade and capital flows. This theory can go some way in accounting for the cross-country differences and the time series variation of financial development. When we recognize that different kinds of institutional heritages afford different scope for private interests to express themselves, we obtain a synthesis between the structural theories and private interest theory, which is supported by the data.

Composite Quasar Spectra from the Sloan Digital Sky Survey

Abstract: We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 A at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s-1, compared with shifts of up to 550 km s-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 A. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 A and -2.45 redward of ≈5000 A. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 A, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.

The Power of Suggestion: Inertia in 401(k) Participation and Savings Behavior

Abstract: This paper analyzes the impact of automatic enrollment on 401(k) savings behavior. We have two key e ndings. First, 401(k) participation is signie cantly higher under automatic enrollment. Second, a substantial fraction of 401(k) participants hired under automatic enrollment retain both the default contribution rate and fund allocation even though few employees hired before automatic enrollment picked this particular outcome. This “ default” behavior appears to result from participant inertia and from employee perceptions of the default as investment advice. These e ndings have implications for the design of 401(k) savings plans as well as for any type of Social Security reform that includes personal accounts over which individuals have control. They also shed light more generally on the importance of both economic and noneconomic (behavioral) factors in the determination of individual savings behavior.

Neighborhood inequality, collective efficacy, and the spatial dynamics of urban violence

Abstract: Highlighting resource inequality, social processes, and spatial interdependence, this study combines structural characteristics from the 1990 census with a survey of 8,872 Chicago residents in 1995 to predict homicide variations in 1996–1998 across 343 neighborhoods. Spatial proximity to homicide is strongly related to increased homicide rates, adjusting for internal neighborhood characteristics and prior homicide. Concentrated disadvantage and low collective efficacy—defined as the linkage of social control and cohesion—also independently predict increased homicide. Local organizations, voluntary associations, and friend/kinship networks appear to be important only insofar as they promote the collective efficacy of residents in achieving social control and cohesion. Spatial dynamics coupled with neighborhood inequalities in social and economic capacity are therefore consequential for explaining urban violence.

Grid information services for distributed resource sharing

Abstract: Grid technologies enable large-scale sharing of resources within formal or informal consortia of individuals and/or institutions: what are sometimes called virtual organizations. In these settings, the discovery, characterization, and monitoring of resources, services, and computations are challenging problems due to the considerable diversity; large numbers, dynamic behavior, and geographical distribution of the entities in which a user might be interested. Consequently, information services are a vital part of any Grid software infrastructure, providing fundamental mechanisms for discovery and monitoring, and hence for planning and adapting application behavior. We present an information services architecture that addresses performance, security, scalability, and robustness requirements. Our architecture defines simple low-level enquiry and registration protocols that make it easy to incorporate individual entities into various information structures, such as aggregate directories that support a variety of different query languages and discovery strategies. These protocols can also be combined with other Grid protocols to construct additional higher-level services and capabilities such as brokering, monitoring, fault detection, and troubleshooting. Our architecture has been implemented as MDS-2, which forms part of the Globus Grid toolkit and has been widely deployed and applied.

The Rational Design of International Institutions

Abstract: Why do international institutions vary so widely in terms of such key institutional features as membership, scope, and flexibility? We argue that international actors are goal-seeking agents who make specific institutional design choices to solve the particular cooperation problems they face in different issue-areas. In this article we introduce the theoretical framework of the Rational Design project. We identify five important features of institutions—membership, scope, centralization, control, and flexibility—and explain their variation in terms of four independent variables that characterize different cooperation problems: distribution, number of actors, enforcement, and uncertainty. We draw on rational choice theory to develop a series of empirically falsifiable conjectures that explain this institutional variation. The authors of the articles in this special issue of International Organization evaluate the conjectures in specific issue-areas and the overall Rational Design approach.

Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data

Abstract: We study the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over ~100 deg2 of high Galactic latitude sky along the celestial equator. The distribution of galaxies in the g*-r* versus u*-g* color-color diagram is strongly bimodal, with an optimal color separator of u*-r* = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies, respectively, to show that the two peaks correspond roughly to early- (E, S0, and Sa) and late-type (Sb, Sc, and Irr) galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late-type galaxies are bluer than early-type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts versus apparent magnitude relations for the two color types are significantly different and demonstrate that the fraction of blue galaxies increases toward the faint end.

Naive Diversification Strategies in Defined Contribution Saving Plans

Abstract: There is a worldwide trend toward defined contribution saving plans and growing interest in privatized social security plans. In both environments, individuals are given some responsibility to make their own asset-allocation decisions, raising concerns about how well they do at this task. This paper investigates one aspect of the task, namely diversification. It is shown that some investors follow the "1/n strategy": they divide their contributions evenly across the funds offered in the plan. Consistent with this naive notion of diversification, it is found that the proportion invested in stocks depends strongly on the proportion of stock funds in the plan.

The Importance of Noncognitive Skills: Lessons from the GED Testing Program

Abstract: It is common knowledge outside of academic journals that motivation, tenacity, trustworthiness, and perseverance are important traits for success in life. Thomas Edison wrote that "genius is 1 percent inspiration and 99 percent perspiration." Most parents read the Aesop fable of the "Tortoise and The Hare" to their young children at about the same time they read them the story of "The Little Train That Could." Numerous instances can be cited of high-IQ people who failed to achieve success in life because they lacked self discipline and low-IQ people who succeeded by virtue of persistence, reliability, and self-discipline. The value of trustworthiness has recently been demonstrated when market systems were extended to Eastern European societies with traditions of corruption and deceit. It is thus surprising that academic discussions of skill and skill formation almost exclusively focus on measures of cognitive ability and ignore noncognitive skills. The early literature on human capital (e.g. Gary Becker, 1964) contrasted cognitive-ability models of earnings with human capital models, ignoring noncognitive traits entirely. The signaling literature (e.g., Michael Spence, 1974), emphasized that education was a signal of a one-dimensional ability, usually interpreted as a cognitive skill. Most discussions of ability bias in the estimated return to education treat omitted ability as cognitive ability and attempt to proxy the missing ability by cognitive tests. Most assessments of school reforms stress the gain from reforms as measured by the ability of students to perform on a standardized achievement test. Widespread use of standardized achievement and ability tests for admissions and educational evaluation are premised on the belief that the skills that can be tested are essential for success in schooling, a central premise of the educational-testing movement since its inception. Much of the neglect of noncognitive skills in analyses of earnings, schooling, and other lifetime outcomes is due to the lack of any reliable measure of them. Many different personality and motivational traits are lumped into the category of noncognitive skills. Psychologists have developed batteries of tests to measure noncognitive skills (e.g., Robert Sternberg, 1985). These tests are used by companies to screen workers but are not yet used to ascertain college readiness or to evaluate the effectiveness of schools or reforms of schools. The literature on cognitive tests ascertains that one dominant factor ("g") summarizes cognitive tests and their effects on outcomes. No single factor has yet emerged to date in the literature on noncognitive skills, and it is unlikely that one will ever be found, given the diversity of traits subsumed under the category of noncognitive skills. Studies by Samuel Bowles and Herbert Gintis (1976), Rick Edwards (1976), and Roger Klein et al. (1991) demonstrate that job stability and dependability are traits most valued by employers as ascertained by supervisor ratings and questions of employers although they present no direct evidence on wages and educational t Discussants: Susan Mayer, University of Chicago; Cecilia Rouse, Princeton University; Nan Maxwell, California State University-Hayward; Janet Currie, University of California-Los Angeles.

Prospect Theory and Asset Prices

Abstract: We study asset prices in an economy where investors derive direct utility not only from consumption but also from fluctuations in the value of their financial wealth. They are loss averse over these fluctuations, and the degree of loss aversion depends on their prior investment performance. We find that our framework can help explain the high mean, excess volatility, and predictability of stock returns, as well as their low correlation with consumption growth. The design of our model is influenced by prospect theory and by experimental evidence on how prior outcomes affect risky choice.

Syndication Networks and the Spatial Distribution of Venture Capital Investments

Abstract: Sociological investigations of economic exchange reveal how institutions and social structures shape transaction patterns among economic actors. This article explores how interfirm networks in the U.S. venture capital (VC) market affect spatial patterns of exchange. Evidence suggests that information about potential investment opportunities generally circulates within geographic and industry spaces. In turn, the circumscribed flow of information within these spaces contributes to the geographic‐ and industry‐localization of VC investments. Empirical analyses demonstrate that the social networks in the VC community—built up through the industry’s extensive use of syndicated investing—diffuse information across boundaries and therefore expand the spatial radius of exchange. Venture capitalists that build axial positions in the industry’s coinvestment network invest more frequently in spatially distant companies. Thus, variation in actors’ positioning within the structure of the market appears to differentia...

Robust Control and Model Uncertainty

Abstract: The following sections are included:IntroductionA Benchmark Resource Allocation ProblemModel MisspecificationTwo Robust Control ProblemsRecursivity of the Multiplier FormulationTwo Preference OrderingsRecursivity of the Preference OrderingsConcluding Remarks

Bounds on Universal Extra Dimensions

Abstract: We show that the bound from the electroweak data on the size of extra dimensions accessible to all the standard model elds is rather loose. These \universal" extra dimensions could have a compactication scale as low as 300 GeV for one extra dimension. This is because the Kaluza-Klein number is conserved and thus the contributions to the electroweak observables arise only from loops. The main constraint comes from weak-isospin violation eects. We also compute the contributions to the S parameter and the Zb b vertex. The direct bound on the compactication scale is set by CDF and D0 in the few hundred GeV range, and the Run II of the Tevatron will either discover extra dimensions or else it could signicantly raise the bound on the compactication scale. In the case of two universal extra dimensions, the current lower bound on the compactication scale depends logarithmically on the ultra-violet cuto of the higher dimensional theory, but can be estimated to lie between 400 and 800 GeV. With three or more extra dimensions, the cuto dependence may be too strong to allow an estimate.

The genic view of the process of speciation

Abstract: The unit of adaptation is usually thought to be a gene or set of interacting genes, rather than the whole genome, and this may be true of species differentiation. Defining species on the basis of reproductive isolation (RI), on the other hand, is a concept best applied to the entire genome. The biological species concept (BSC; Mayr, 1963) stresses the isolation aspect of speciation on the basis of two fundamental genetic assumptions ‐ the number of loci underlying species differentiation is large and the whole genome behaves as a cohesive, or coadapted genetic unit. Under these tenets, the exchange of any part of the genomes between diverging groups is thought to destroy their integrity. Hence, the maintenance of each species’ genome cohesiveness by isolating mechanisms has become the central concept of species. In contrast, the Darwinian view of speciation is about differential adaptation to different natural or sexual environments. RI is viewed as an important by product of differential adaptation and complete RI across the whole genome need not be considered as the most central criterion of speciation. The emphasis on natural and sexual selection thus makes the Darwinian view compatible with the modern genic concept of evolution. Genetic and molecular analyses of speciation in the last decade have yielded surprisingly strong support for the neo-Darwinian view of extensive genetic differentiation and epistasis during speciation. However, the extent falls short of what BSC requires in order to achieve whole-genome ‘cohesiveness’. Empirical observations suggest that the gene is the unit of species differentiation. Significantly, the genetic architecture underlying RI, the patterns of species hybridization and the molecular signature of speciation genes all appear to support the view that RI is one of the manifestations of differential adaptation, as Darwin (1859, Chap. 8) suggested. The nature of this adaptation may be as much the result of sexual selection as natural selection. In the light of studies since its early days, BSC may now need a major revision by shifting the emphasis from isolation at the level of whole genome to differential adaptation at the genic level. With this revision, BSC would in fact be close to Darwin’s original concept of speciation.

Do People Mean What They Say? Implications for Subjective Survey Data

Abstract: Four main messages emerge from the study of subjective survey data. First, a large experimental literature by and large supports economists' skepticism of subjective questions. Second, put in an econometric framework, these findings cast serious doubts on attempts to use subjective data as dependent variables, because the measurement error appears to correlate with a large set of characteristics in behaviors. Third, these data may be useful as explanatory variables. Finally, the empirical work suggests that subjective variables are useful in practice for explaining differences in behavior across individuals. Changes in answers to these questions, however, do not appear useful in explaining changes in behavior.

Spectroscopic Target Selection for the Sloan Digital Sky Survey: The Luminous Red Galaxy Sample

Abstract: We describe the target selection and resulting properties of a spectroscopic sample of luminous red galaxies (LRGs) from the imaging data of the Sloan Digital Sky Survey (SDSS). These galaxies are selected on the basis of color and magnitude to yield a sample of luminous intrinsically red galaxies that extends fainter and farther than the main flux-limited portion of the SDSS galaxy spectroscopic sample. The sample is designed to impose a passively evolving luminosity and rest-frame color cut to a redshift of 0.38. Additional, yet more luminous red galaxies are included to a redshift of ~0.5. Approximately 12 of these galaxies per square degree are targeted for spectroscopy, so the sample will number over 100,000 with the full survey. SDSS commissioning data indicate that the algorithm efficiently selects luminous (M^+_g ≈ -21.4) red galaxies, that the spectroscopic success rate is very high, and that the resulting set of galaxies is approximately volume limited out to z = 0.38. When the SDSS is complete, the LRG spectroscopic sample will fill over 1 h^(-3) Gpc^3 with an approximately homogeneous population of galaxies and will therefore be well suited to studies of large-scale structure and clusters out to z = 0.5.

Complexities of CD28/B7: CTLA-4 Costimulatory Pathways in Autoimmunity and Transplantation

Abstract: Recent advances in the understanding of T cell activation have led to new therapeutic approaches in the treatment of immunological disorders. One attractive target of intervention has been the blockade of T cell costimulatory pathways, which result in more selective effects on only those T cells that have encountered specific antigen. In fact, in some instances, costimulatory pathway antagonists can induce antigen-specific tolerance that prevents the progression of autoimmune diseases and organ graft rejection. In this review, we summarize the current understanding of these complex costimulatory pathways including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2 (CD86) molecules. We present evidence that suggests that multiple mechanisms contribute to CD28/B7-mediated T cell costimulation in disease settings that include expansion of activated pathogenic T cells, differentiation of Th1/Th2 cells, and the migration of T cells into target tissues. Additionally, the negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection supports a dynamic but complex process of immune regulation that is prominent in the control of self-reactivity. This is most apparent in regulation of the CD4(+)CD25(+)CTLA-4(+) immunoregulatory T cells that control multiple autoimmune diseases. The implications of these complexities and the potential for use of these therapies in clinical immune intervention are discussed.

The Role of Social Capital in Financial Development

Abstract: To identify the effect of social capital on financial development, we exploit the well-known differences in social capital (Banfield (1958), Putnam (1993)) across different parts of Italy. In areas of the country with high levels of social capital, households invest less in cash and more in stock, are more likely to use checks, have higher access to institutional credit, and make less use of informal credit. The effect of social capital is stronger where legal enforcement is weaker and among less-educated people. These results are not driven by omitted environmental variables, since we show that the behavior of movers is still affected by the level of social capital present in the province where they were born.