Showing papers by "University of Chicago published in 1984"

Financial Intermediation and Delegated Monitoring

Abstract: This paper develops a theory of financial intermediation based on minimizing the cost of monitoring information which is useful for resolving incentive problems between borrowers and lenders. It presents a characterization of the costs of providing incentives for delegated monitoring by a financial intermediary. Diversification within an intermediary serves to reduce these costs, even in a risk neutral economy. The paper presents some more general analysis of the effect of diversification on resolving incentive problems. In the environment assumed in the model, debt contracts with costly bankruptcy are shown to be optimal. The analysis has implications for the portfolio structure and capital structure of intermediaries.

Reducing Bias in Observational Studies Using Subclassification on the Propensity Score

Abstract: The propensity score is the conditional probability of assignment to a particular treatment given a vector of observed covariates. Previous theoretical arguments have shown that subclassification on the propensity score will balance all observed covariates. Subclassification on an estimated propensity score is illustrated, using observational data on treatments for coronary artery disease. Five subclasses defined by the estimated propensity score are constructed that balance 74 covariates, and thereby provide estimates of treatment effects using direct adjustment. These subclasses are applied within sub-populations, and model-based adjustments are then used to provide estimates of treatment effects within these sub-populations. Two appendixes address theoretical issues related to the application: the effectiveness of subclassification on the propensity score in removing bias, and balancing properties of propensity scores with incomplete data.

The 2 Sigma Problem: The Search for Methods of Group Instruction as Effective as One-to-One Tutoring:

Abstract: T w o University of Chicago doctoral students in education, Anania (1982, 1983) and Burke (1984), completed dissertations in which they compared student learning under the following three conditions of instruction: 1. Conventional. Students learn the subject matter in a class with about 30 students per teacher. Tests are given periodically for marking the students. 2. Mastery Learning. Students learn the subject matter in a class with about 30 students per teacher. The instruction is the same as in the conventional class (usually with the same teacher). Formative tests (the same tests used with the conventional group) are given for feedback followed by corrective procedures and parallel formative tests to determine the extent to which the students have mastered the subject matter. 3. Tutoring. Students learn the subject matter with a good tutor for each student (or for two or three students simultaneously). This tutoring instruction is followed periodically by formative tests, feedback-corrective procedures, and parallel formative tests as in the mastery learning classes. It should be pointed out that the need for corrective work under tutoring is very small.

Organization Strategy and Structural Differences for Radical Versus Incremental Innovation

Abstract: The purpose of this study was to test a model of the organizational innovation process that suggests that the strategy-structure causal sequence is differentiated by radical versus incremental innovation. That is, unique strategy and structure will be required for radical innovation, especially process adoption, while more traditional strategy and structure arrangements tend to support new product introduction and incremental process adoption. This differentiated theory is strongly supported by data from the food processing industry. Specifically, radical process and packaging adoption are significantly promoted by an aggressive technology policy and the concentration of technical specialists. Incremental process adoption and new product introduction tends to be promoted in large, complex, decentralized organizations that have market dominated growth strategies. Findings also suggest that more traditional structural arrangements might be used for radical change initiation if the general tendencies that occur in these dimensions as a result of increasing size can be delayed, briefly modified, or if the organization can be partitioned structurally for radical vs. incremental innovation. In particular, centralization of decision making appears to be necessary for radical process adoption along with the movement away from complexity toward more organizational generalists. This suggests that a greater support of top managers in the innovation process is necessary to initiate and sustain radical departures from the past for that organization.

Monoclonal antibodies localize oestrogen receptor in the nuclei of target cells.

Abstract: Although it is widely accepted that specific intracellular receptor proteins are involved in the oestrogenic regulation of gene expression and growth in reproductive tissues, the precise nature of the regulation is poorly understood. Among the unresolved issues are the distribution and dynamics of the oestrogen receptor protein (oestrophilin) in target tissues in the presence and absence of oestrogens and antioestrogens. The use of radio-labelled and unlabelled receptor ligands to detect and measure oestrogen receptors in tissues has been complicated by the presence of other intracellular steroid-binding proteins1 and by the low concentration of receptors in responsive tissues. We report here the development of an immunocytochemical procedure that is suitable for localizing oestrophilin directly in frozen tissue sections or cells from human and several non-human sources. When monoclonal antibodies to oestrophilin were used to detect receptor in various oestrogen-sensitive tissues, specific staining was confined to the nucleus of all stained cells, suggesting that both cytosol and nuclear forms of the receptor protein may reside in the nuclear compartment.

On the measurement of natural and sexual selection: theory.

Abstract: The aim of this paper is to illustrate an approach to the empirical measurement of selection that is directly related to formal evolutionary theory. Recent field studies have demonstrated that it is feasible to measure fitness in natural populations. The most successful studies have yielded accurate tallies of survivorship, mating success and fertility (e.g., Tinkle, 1965; Howard, 1979; Downhower and Brown, 1980; Lennington, 1980; Kluge, 1981; Clutton-Brock et al., 1982). Despite this success, no concensus has been reached on how to analyze the data and relate them to evolutionary theory. We present here a mode of data analysis that describes selection in useful, theoretical terms, so that field or experimental results will have a tangible relationship to equations for evolutionary change. Multivariate, polygenic theory (Lande, 1979, 1980, 1981; Bulmer, 1980) is particularly useful as a conceptual framework because it is concerned with the evolution of continuously distributed traits such as those commonly studied in laboratory and field situations. Multivariate equations have been used for many years by plant and animal breeders in order to impose selection and predict its impact (Smith, 1936; Hazel, 1943; Dickerson et al., 1954, 1974; Yamada, 1977), but this quantitative genetic theory has only recently been applied to evolutionary problems. Definitions and Aims. -It is critical to distinguish between selection and evolutionary response to selection (Fisher, 1930; Haldane, 1954). Selection causes observable changes within a generation in the means, variances and covariances of phenotypic distributions. Thus selection can be described in purely phenotypic terms without recourse to the inheritance of characters. In contrast, evolutionary response to selection, for example, the change in phenotypic mean from one generation to the next, certainly does depend on inheritance. In the following sections we show how knowledge of inheritance can be combined with purely phenotypic measures of selection to predict evolutionary response to selection. By distinguishing between selection and response to selection we can measure selection on characters whose mode of inheritance may be unknown and make prediction of evolutionary response a separate issue. Thus knowledge of inheritance is essential for complete

Conformal Invariance, Unitarity, and Critical Exponents in Two Dimensions

Abstract: Conformal invariance and unitarity severely limit the possible values of critical exponents in two-dimensional systems.

The dirichlet problem for nonlinear second‐order elliptic equations I. Monge‐ampégre equation

Abstract: On considere le probleme de Dirichlet pour des equations elliptiques non lineaires pour une fonction reelle u definie dans la fermeture Ω d'un domaine borne Ω dans R n avec une frontiere ∂Ω C ∞

Culture and the Development of Everyday Social Explanation

Abstract: The impact of cultural meaning systems on the development of everyday social explanation is explored in a cross-cultural investigation undertaken among Indian and American adults and children (ages 8, 11, and 15 year). It is demonstrated that at older ages Americans make greater reference to general dispositions and less reference to contextual factors in explanation than do Hindus . References to general dispositions also undergo a much greater developmental increase among Americans than among Hindus , whereas references to contextual factors show the opposite pattern of developmental change. Evidence suggests that these cross-cultural and developmental differences result from contrasting cultural conceptions of the person acquired over development in the two cultures rather than from cognitive., experiential, or informational differences between attributors . Discussion focuses on theoretical implications of such a demonstration for understanding: (a) the importance of integrating semantic with structural considerations in theories of social attribution, (b) the need to develop nonteleological frameworks for interpreting age and cultural diversity in conceptualization, and (c) the role of cultural communication in the acquisition of everyday social knowledge.

On the measurement of natural and sexual selection: applications.

Abstract: In this paper, we use measures of selection developed by quantitative geneticists and some new results (Arnold and Wade, 1984) to analyze multiple episodes of selection in natural populations of amphibians, reptiles, and insects. These examples show how different methods of data collection influence the potential for relating field observations to formal evolutionary theory. We adhere to the Darwinian tradition of distinguishing between natural and sexual selection (Darwin, 1859, 1871; Ghiselin, 1974). We view sexual selection as selection arising from variance in mating success and natural selection as arising from variance in other components of fitness. The justification for this formal distinction is developed by Wade (1979), Lande (1980), Wade and Arnold (1980), Arnold and Houck (1982) and Arnold (1 983 a). (We define mating success as the number of mates that bear progeny given survival of the mating organsim to sexual maturity. We do not equate mating success with mere copulatory success.) The utility of the distinction between sexual and natural selection is that the two forms of selection may often act in opposite directions on particular characters (Darwin, 1859, 1871). While we find the distinction between these two forms of selection useful, the difference is not crucial to our analysis. The essential point is that the recognition of selection episodes permits analysis of selection that may change in magnitude and direction during the life cycle. Defining Fitness Components. -The key first step in the analysis of data is to define multiplicative components of fitness so that selection can be partitioned into parts corresponding to these components or episodes of selection. Using an animal example, if the number of offspring zygotes is taken as total fitness, we can define the following components of fitness: viability (survivorship to sexual maturity), mating success (the number of mates) and fertility per mate (the average number of zygotes produced per mate). These components of fitness are defined so that their product gives total fitness. As a second example, consider the components of fitness in a plant in which yield (seeds/plant) is taken as the measure of total fitness (Primack and Antonovics, 1981). We might define the following components of fitness: number of stems per plant, average number of inflorescences per stem, average number of seed capsules per inflorescence, and average number of seeds per capsule. Again, these four fitness components are defined so that their product gives total fitness. We will need to measure each component of fitness and each character on each individual in order to partition selection into parts corresponding to the separate episodes of selection or to the separate components of fitness. Thus in the animal example, we need to measure the viability, mating success and fertility of each individual. With this accomplished we can estimate the separate forces of viability, sexual and fertility selection on each phenotypic character. In addition we can calculate the opportunities of selection corresponding to these three episodes and covariances between the different kinds of selection. In the plant example, we might begin with the intuition that larger plants have a greater yield. Using our methodology we can reword and extend this intuition. We can not only test the proposition of

A kinetic model of Phanerozoic taxonomic diversity; III, Post-Paleozoic families and mass extinctions

Abstract: A three-phase kinetic model with time-specific perturbations is used to describe large-scale patterns in the diversification of Phanerozoic marine families. The basic model assumes that the Cambrian, Paleozoic, and Modern evolutionary faunas each diversified logistically as a consequence of early exponential growth and of later slowing of growth as the ecosystems became filled; it also assumes interaction among the evolutionary faunas such that expansion of the combined diversities of all three faunas above any single fauna's equilibrium caused that fauna's diversity to begin to decline. This basic model adequately describes the diversification of the evolutionary faunas through the Paleozoic Era as well as the asymmetrical rise and fall of background extinction rates through the entire Phanerozoic. Declines in diversity and changes in faunal dominance associated with mass extinctions can be accommodated in the model with short-term accelerations in extinction rates or declines in equilibria. Such accelerations, or perturbations, cause diversity to decline exponentially and then to rebound sigmoidally following release. The amount of decline is dependent on the magnitude and duration of the perturbation, the timing of the perturbation with respect to the diversification of the system, and the system's initial per-taxon rates of diversification and turnover. When applied to the three-phase model, such perturbations describe the changes in diversity and faunal dominance during and after major mass extinctions, the long-term rise in total diversity following the Late Permian and Norian mass extinctions, and the peculiar diversification and then decline of the remnants of the Paleozoic fauna during the Mesozoic and Cenozoic Eras. The good fit of this model to data on Phanerozoic familial diversity suggests that many of the large-scale patterns of diversification seen in the marine fossil record of animal families are simple consequences of nonlinear interrelationships among a small number of parameters that are intrinsic to the evolutionary faunas and are largely (but not completely) invariant through time.

A Price Discrimination Theory of Coupons

Abstract: The objective of this paper is to analyze the consumer's decision in electing to use cents-off coupons distributed by manufacturers of consumer products. Arguing that the decision to use coupons is based on the tradeoff between costs of using coupons and the savings obtained, it is shown that coupons can serve as a price discrimination device to provide a lower price to a particular segment of consumers. Based on a price theoretic model, it is shown that the users of coupons are more price elastic than nonusers of coupons and that the opportunity cost of time and other household resource variables are determinant factors in consumers' decisions. Implications derived from the model are tested using diary panel data.

Variation among floral visitors in pollination ability: a precondition for mutualism specialization.

Abstract: The unusual floral biology of a neotropical herb provided an opportunity to determine that floral visitors varied significantly in their ability to effect fruit-set. Pollination efficiency and visitation frequency varied among Hymenoptera (five taxa), which were responsible for 99 percent of all fruits set. Lepidoptera (four taxa) were common visitors but poor pollinators. These results indicate that flower visitors vary in their beneficial effects on plants, fulfilling one of the primary conditions required for the specialization of plants on pollinators.

A New Approach for Testing the Significance of Differences Between ROC Curves Measured from Correlated Data

Abstract: Receiver Operating Characteristic analysis is now generally recognized as the most appropriate methodology for evaluating the diagnostic performance of medical imaging procedures (1–7). ROC analysis has been used in the field of psychophysics for three decades, and its theory and experimental methodology have been developed in considerable detail (8–13). Perhaps surprisingly, the statistical properties of ROC measures had received relatively little attention until several years ago, when the limited size of practical data sets in medical applications indicated the need for careful study of this issue. Recent progress in the statistical analysis of ROC data includes the work of Metz and Kronman (14,15), who developed a bivariate test for the statistical significance of differences between ROC curves measured from independent data sets; the work of Hanley and McNeil, who studied the statistical properties of the area under an ROC curve and developed techniques to predict the number of cases required tc demonstrate the significance of differences between ROC “Area Indexes” measured from either independent (16) or correlated (17) data sets; and the work of Swets and Pickett (7), who identified three components of variation in ROC measures and outlined a general statistical protocol for testing the significance of differences in the Area Index.

What happens when an accelerating observer detects a Rindler particle

Abstract: The nature of the interaction between a quantum field and an accelerating particle detector is analyzed from the point of view of an inertial observer. It is shown in detail for the simple case of a two-level detector how absorption of a Rindler particle corresponds to emission of a Minkowski particle. Several apparently paradoxical aspects of this process related to causality and energy conservation are discussed and resolved.

Retarding Effect of Lowered Heart Rate on Coronary Atherosclerosis

Abstract: The role of heart rate in the development of coronary atherosclerosis was assessed in adult male cynomolgus monkeys (Macaca fascicularis). Heart rate was lowered in six animals by surgical ablation of the sinoatrial node. A sham procedure, which included all of the surgical steps except for sinoatrial node ablation, was carried out in eight animals. All of the monkeys were fed an atherogenic high cholesterol diet for 6 months, and heart rates were monitored repeatedly by telemetry during 24-hour test periods. Coronary atherosclerosis in animals with postoperative heart rates less than the preoperative mean for all of the animals that underwent surgery was less than half that of animals with heart rates above the mean or of diet-fed control animals not subjected to surgery. Groups did not differ in blood pressure, serum lipids, or body weight. These results suggest that heart rate in itself may contribute to the mechanisms by which behavioral patterns and physical training influence coronary artery disease.

Technical guidelines for assessing computerized adaptive tests

Abstract: Guidelines are proposed for evaluating a computerized adaptive test. Topics include dimensionality, measurement error, validity, estimation of item parameters, item pool characteristics and human factors. Equating CAT and conventional tests is considered and matters of equity are addressed.