Showing papers on "Population published in 1981"

Introduction to quantitative genetics

Abstract: Part 1 Genetic constitution of a population: Hardy-Weinberg equilibrium. Part 2 Changes in gene frequency: migration mutation. Part 3 Small populations - changes in gene frequency under simplified conditions. Part 4 Small populations - less simplified conditions. Part 5 Small populations - pedigreed populations and close inbreeding. Part 6 Continuous variation. Part 7 Values and means. Part 8 Variance. Part 9 Resemblance between relatives. Part 10 Heritability. Part 11 Selection - the response and its prediction. Part 12 Selection - the results of experiments. Part 13 Selection - information from relatives. Part 14 Inbreeding and crossbreeding - changes of mean value. Part 15 Inbreeding and crossbreeding - changes of variance. Part 16 Inbreeding and crossbreeding - applications. Part 17 Scale. Part 18 Threshold characters. Part 19 Correlated characters. Part 20 Metric characters under natural selection.

The Causes of Cancer: Quantitative Estimates of Avoidable Risks of Cancer in the United States Today

Abstract: My lecture spanned not only the hour allocated for it in the morning, but also the first half of the round table that afternoon, where it acted as an introduction to the round table discussion that followed. The break between the two sessions was determined only by administrative and not by scientific matters, and so in this published account, the two may be read as a unit.

Models of speciation by sexual selection on polygenic traits

Abstract: The joint evolution of female mating preferences and secondary sexual characters of males is modeled for polygamous species in which males provide only genetic material to the next generation and females have many potential mates to choose among. Despite stabilizing natural selection on males, various types of mating preferences may create a runaway process in which the outcome of phenotypic evolution depends critically on the genetic variation parameters and initial conditions of a population. Even in the absence of genetic instability, rapid evolution can result from an interaction of natural and sexual selection with random genetic drift along lines of equilibria. The models elucidate genetic mechanisms that can initiate or contribute to rapid speciation by sexual isolation and divergence of secondary sexual characters.

Minimum Population Sizes for Species Conservation

Abstract: Many species cannot survive in mandominated habitats. Reserves of essentially undisturbed habitat are necessary if such species are to survive in the wild. Aside from increased efforts to accelerate habitat acquisition for such species, the most pressing need facing conservationists is development of a predictive understanding of the relationship between a population's size and its chances of extinction. Biologists have long known that the smaller the population, the more susceptible it is to extinction from various causes. During the current era of heightened competition for use of the world's remaining wildlands, this qualitative understanding is of limited utility to conservation and natural resource planners. The old adage that "the bigger the reserve, the better" must be replaced with more precise prescriptions for how much land is enough to achieve conservation objectives. Efforts at making such determinations have been clouded by inconsistencies in the focus on the unit to be preserved (population, species, community, ecosystem) and lack of an explicit definition of what constitutes successful preservation (persistence for 10, 100, 1000 years, etc.). The intricate interdependencies of living things dictate that conservation efforts be focused on the community and ecosystem level. Unfortunately, the very magnitude of complexity of these systems makes such efforts difficult. Moreover, certain species are more sensitive than others to changing conditions and begin to decline prior to any noticeable degradation of the community to which they belong. Consequently, conservation efforts have been and, in many cases, will continue to be at the singlespecies level. Many species currently in jeopardy are large-bodied and/or specialized, two characteristics that usually

A new prognostic classification of chronic lymphocytic leukemia derived from a multivariate survival analysis.

Abstract: Survivals of two series of CLL patients (99 from a retrospective series and 196 from a prospective series) were studied separately The three main staging systems (Rai, Binet, Rundles) agreed well, but as far as survival is concerned, too many stages are defined The authors performed a Cox multivariate analysis of survival in order to isolate important prognostic factors at diagnosis and to use them to build a simple three-stage classification Thrombopenia and anemia appeared as the most important risk factors Among the nonanemic and nonthrombopenic patients, the number of involved areas was clearly related to prognosis in the authors' two series This study allowed the authors to propose a new classification in three prognostic groups Group C: anemia (Hb less than 10 g) and/or thrombopenia (platelets less than 100,000/mm3); about 15% of the patients; median of 2 years Group B: no anemia, no thrombopenia, three or more involved areas (counting as one each of the following: axillary, cervical, inguinal, lymph nodes, whether unilateral or bilateral, spleen and liver); about 30% of patients; median of 7 years Group A: no anemia, no thrombopenia, less than three involved areas; about 55% of patients; the survival of this group does not seem different from that of the French population of the same age and sex distribution This three-stage classification only requires clinical examination and routine hemogram, has a good prognostic value which was confirmed on the series of Montserrat and Rozman (146 patients), and should therefore be helpful in planning new clinical trials

The nutritional ecology of immature insects

Abstract: An understanding of insect ecology has been hampered by an inadequate knowledge of nutritional physiology. The effects of food quality upon physi­ ology and behavior (24, 102, 185, 285) and at the population and ecosystem levels (107, 209) are too often neglected. Nutritional ecology is central to proper interpretations of life history phenomena (e.g. manner of feeding, habitat selection, defense, and reproduction) both in ecological and evolu­ tionary time. Careful consideration of present and future information on this topic can lead to better predictive capabilities in both coevolutionary theory and pest management. In this review we assess the importance of food quality relative to other environmental factors and organism adaptations that influence post-inges­ tive food utilization and growth performance of immature arthropods. Reviewed elsewhere are pre-ingestive factors affecting food choice and con­ sumption (52, 73, 142, 154), nutritional requirements (67, 129, 226, 252), and the physiology of food consumption and utilization (19, 130, 270).

The Masterpiece of Nature: The Evolution and Genetics of Sexuality

Abstract: Originally published in 1982, The Masterpiece of Nature examines sex as representative of the most important challenge to the modern theory of evolution. The book suggests that sex evolved, not as the result of normal Darwinian processes of natural selection, but through competition between populations or species - a hypothesis elsewhere almost universally discredited. The book also discusses the nature of sex and its consequences for the individual and for the population, as well as various other theories of sex. Since the value of these theories is held to reside wholly in their ability to predict the patterns of sexuality observed in nature, the book seeks to provide an extensive review of the circumstances in which sexuality is attenuated or lost throughout the animal kingdom, and these facts are then used to weigh up the merits of the rival theories. This book will be of interest to researchers in the area of genetics, ecology and evolutionary biology.

Exploitation Ecosystems in Gradients of Primary Productivity

Abstract: Based on the assumption that each trophic level acts as a single exploitative population, a model relating the trophic structure of ecosystems to their potential primary productivity is developed. According to the model, herbivory pressure should be most severe in relatively unproductive environments. With increased potential productivity, the role of predation in herbivore regulation should become more important and the impact of herbivory upon plant communities should decrease. In very productive environments, increase in herbivory pressure is again probable, at least in aquatic ecosystems. The predicted pattern of phytomass and predicted results of manipulations are compared with available data. A reasonable fit between predictions and observations is found, although the sparsity of data and methodological uncertainties weaken the corroboration in several cases. In terrestrial ecosystems, the present version of the model seems best applicable to the vertebrate branch of the grazing chain, whereas the a...

Job decision latitude, job demands, and cardiovascular disease : a prospective study of Swedish men

Abstract: The association between specific job characteristics and subsequent cardiovascular disease was tested using a large random sample of the male working Swedish population. The prospective development of coronary heart disease (CHD) symptoms and signs was analyzed using a multivariate logistic regression technique. Additionally, a case-controlled study was used to analyze all cardiovascular-cerebrovascular (CHD-CVD) deaths during a six-year follow-up. The indicator of CHD symptoms and signs was validated in a six-year prospective study of CHD deaths (standardized mortality ratio 5.0; p less than or equal to .001). A hectic and psychologically demanding job increases the risk of developing CHD symptoms and signs (standardized odds ratio 1.29, p less than 0.25) and premature CHD-CVD death (relative risk 4.0, p less than .01). Low decision latitude-expressed as low intellectual discretion and low personal schedule freedom-is also associated with increased risk of cardiovascular disease. Low intellectual discretion predicts the development of CHD symptoms and signs (SOR 1.44, p less than .01), while low personal schedule freedom among the majority of workers with the minimum statutory education increases the risk of CHD-CVD death (RR 6.6, p less than .0002). The associations exist after controlling for age, education, smoking, and overweight.

The Ultimate Resource

Abstract: Arguing that the ultimate resource is the human spirit, Julian Simon has led a vigorous challenge to conventional beliefs about scarcity of energy and natural resources, pollution of the environment, the effects of immigration, and the "perils of overpopulation". This new volume is updated and provides theory for the observed trends: population growth and increased income put pressure on supplies of resources. This increases prices, which provides opportunities and incentive for innovation. Eventually the innovative responses are so successful that prices end up below what they were before the shortage occurred. The book also tackles timely issues such as the supposed rate of species extinction, the "vanishing farmland crisis", and the wastefulness of coercive recycling. In Simon's view, the key factor in natural and world economic growth is our capacity for the creation of new ideas and contributions to knowledge. The more people alive who can be trained to help solve the problems that confront us, the faster we can remove obstacles, and the greater the economic inheritance we shall bequeath to our descendants. In conjunction with the size of the educated population, the key constraint on human progress is the nature of the economic-political system: talented people need economic freedom and security to bring their talents to fruition.

Cellular and dynamic aspects of oocyte growth in teleosts

Abstract: SYNOPSIS. Four principal stages of oocyte growth are recognized among teleosts. During gonadotropin-independent primary growth, multiple nucleoli form as well as a Balbiani body which eventually disperses throughout the ooplasm. The first gonadotropin-dependent stage involves the formation of yolk vesicles, the precursors to the cortical alveoli. True vitellogenesis follows during which vitellogenin is sequestered from the maternal blood and packaged into yolk granules or spheres. The latter generally fuse centripetally at some time during oocyte growth to give a continuous fluid phase surrounded by a peripheral layer of cytoplasm containing the cortical alveoli. Maturation represents the final stage and is accompanied in many teleosts by water uptake; among marine teleosts with pelagic eggs, most of the final egg volume may be achieved by this process. Ovaries may be synchronous, asynchronous, or group-synchronous. Among the latter, a clutch of oocytes may be recruited from an asynchronous population of earlier stages into any of the subsequent stages. In teleosts which spawn repeatedly, recruitment of new clutches can usually be associated with the transition of a previously recruited clutch from one stage to the next. Teleosts thus offer examples of virtually every conceivable type of ovarian physiology and provide a wealth of experimental material for exploring the cellular and hormonal mechanisms which regulate oocyte recruitment and growth throughout ovarian recrudescence.

Use of resonance energy-transfer to monitor membrane-fusion

Abstract: An assay for vesicle--vesicle fusion involving resonance energy transfer between N-(7-nitro-2,1,3-benzoxadiazol-4-yl), the energy donor, and rhodamine, the energy acceptor, has been developed. The two fluorophores are coupled to the free amino group of phosphatidylethanolamine to provide analogues which can be incorporated into a lipid vesicle bilayer. When both fluorescent lipids are in phosphatidylserine vesicles at appropriate surface densities (ratio of fluorescent lipid to total lipid), efficient energy transfer is observed. When such vesicles are fused with a population of pure phosphatidylserine vesicles by the addition of calcium, the two probes mix with the other lipids present to form a new membrane. This mixing reduces the surface density of the energy acceptor resulting in a decreased efficiency of resonance energy transfer which is measured experimentally. These changes in transfer efficiency allow kinetic and quantitative measurements of the fusion process. Using this system, we have studied the ability of phosphatidylcholine, phosphatidylserine, and phosphatidylcholine--phosphatidylserine (1:1) vesicles to fuse with cultured fibroblasts. Under the conditions employed, the majority of the cellular uptake of vesicle lipid could be attributed to the adsorption of intact vesicles to the cell surface regardless of the composition of the vesicle bilayer.

Limiting dilution assays for the determination of immunocompetent cell frequencies. I. Data analysis.

Abstract: A statistical method was developed for the analysis of experimental data from limiting dilution assays. Formulas for the estimation of the frequency of immunocompetent cells within a test population were derived by the statistical methods of weighted averaging, likelihood maximization, and X2 minimization. Equations for the latter 2 were solved by Newton's method of iterative approximation. Estimates obtained by these methods were found to be more valid than those obtained by least squares (LS) fitting as judged by the X2 test and as established by Monte Carlo experiments. X2 minimization was chosen as the preferable estimation method with maximum accuracy and precision (minimum bias and variance) for the standard determination of frequencies; likelihood maximization was used only for the confirmation of results. When data from previously published experiments were reanalyzed, both results and conclusions were found to differ significantly from those originally obtained by LS fitting, thus demonstrating the importance of using proper data analysis methods. In conjunction with the use of available calculators or microcomputers, the method presented here provides a simple and rapid procedure for the valid determination of immunocompetent cell frequencies.

Transport of Steroid Hormones: Binding of 21 Endogenous Steroids to Both Testosterone-Binding Globulin and Corticosteroid-Binding Globulin in Human Plasma

Abstract: This report describes a model of steroid transport in human plasma. The binding affinities of 21 endogenous steroids for both testosterone-binding globulin (TeBG) and corticosteroid-binding globulin (CBG) were determined under equilibrium conditions using a solid phase method at physiological pH and temperature. A computer program was used to solve the complex equilibrium interactions between these steroids and TeBG, CBG, and albumin. In this manner, we calculated the plasma distribution of each steroid into TeBG-bound, CBG-bound, albumin-bound, and unbound fractions in normal men, normal women during both the follicular and luteal phases of the ovarian cycle, and women during the third trimester of a normal pregnancy.

The quantification of ageing and survival in orthodox seeds

Abstract: Orthodox seed ageing, survival and longevity are discussed in relation to environmental factors during storage. It is explained why it has been necessary to introduce a new improved viability equation to quantify the relationship between seed longevity and storage environment. This new equation may be applied to predict the viability of seed lots of all cultivars of species after any period under a very wide range of storage environments. Other symptoms of seed deterioration which occur before death are discussed in terms of both the individual and the population. Evidence is presented for a model which represents and quantifies the development of ageing symptoms in seed lots.

The Population Dynamics of Microparasites and Their Invertebrate Hosts

Abstract: We show how directly transmitted microparasites, broadly defined to include viruses, bacteria, protozoans and fungi, may regulate natural populations of invertebrate hosts. The study combines elements of conventional epidemiology (where the host population is assumed constant) with elements of prey-predator studies (which conventionally emphasize how prey and predator populations may be regulated by their interaction). To this end, we construct simple models embodying the essentials of the dynamical interaction between invertebrate hosts and their directly transmitted microparasites. In successive refinements, these models include the effects of recovery and disease-induced mortality, castration or diminished reproduction of infected hosts, vertical transmission, latent periods of infection, stress-related pathogenicity, the interplay between disease and other density-dependent constraints on host population growth, and free-living infective stages. In analysing the dynamical behaviour of these models, we focus on: the possible regulation of the host population by the parasite; the basic reproductive rate of the parasite, and the way in which it affects the dynamics and the evolution of the host-parasite association; and the threshold host density and its implications for endemic or epidemic maintenance of the infection. These are examined in the light of synoptic compilations of field and laboratory data on: birth rates (and disease-induced reduction thereof), natural death rates and disease-induced death rates of hosts; latent periods and efficiencies of vertical transmission of pathogens; the rate of production and lifetime of free-living infective stages; and some characteristics of long-term cycles and of epidemic outbreaks of disease in forest insects. In particular, our models suggest that the baculovirus and microsporidian infections of many temperate forest insects will tend to produce stable cycles in host abundance and in prevalence of infection, with periods in the range 5-12 years. Enough is known about the European larch budmoth and an associated granulosis virus for us to undertake a detailed comparison between theory and data that strongly suggests that the observed 9-10 year cycles are driven by the host-parasite interaction. We also discuss the possible control of invertebrate pest species by pathogens, showing how our models could guide laboratory or field studies, to help estimate whether a given pathogen is capable of regulating the target pest population, and, if so, roughly what quantity is needed to effect a specific level of (local) control. Throughout, the emphasis is on the biological ingredients of the models, and on the biological conclusions to be drawn; mathematical details are given in appendixes.

Kaposis sarcoma and Pneumocystis pneumonia among homosexual men--New York City and California.

Abstract: Accurate incidence and mortality rates in the US for Kaposis sarcoma are not available but the annual incidence has been estimated at 0.02-0.06/100000. The disease has tended to affect primarily elder males. A departure from this pattern is the diagnosis in the past 30 months of Kaposis sarcoma in 26 homosexual men in New York City and California whose mean age was 39 years (range 26-51 years). In contrast to the clinical course in elderly men in whom the mean survival time is 8-13 years after diagnosis 8 of the homosexual patients died within 2 years after diagnosis. A review of the New York University Coordinated Cancer Registry for Kaposis sarcoma revealed no such cases in men under 50 years of age for the 1970-79 period. Presenting complaints in 20 of the homosexual men included skin lesions only (50%) and skin lesions plus lymphadenopathy (20%). After the initial physician visit 6 patients developed pneumonia and 1 had necrotizing toxoplasmosis of the central nervous system. Serologic evidence of past or present cytomegalovirus infection was found in all 12 patients who were tested. Also of concern is the incidence of 15 cases of Pneumocystis in homosexual men in California since 1979. These findings indicate that physicians should be alert for Kaposis sarcoma Pneumocystis pneumonia and other opportunistic infections associated with immunosuppression in homosexual men.

A Theory of Habitat Selection

Abstract: A graphical theory of habitat selection is built in steps. The theory treats two species in an environment with two usable patch types in a matrix of unusable space. The first step assumes habitat selection is density independent and free of search costs. The second assumes density independence, and the third assumes neither. The first two steps produce results already known from earlier theories. The third, however, requires a new analytical device, the isoleg, which is a line in a two—dimensional—state space of the two species' densities. An isoleg is a set of points in such a density space, such that on one side of the set, individuals of a species optimize their foraging by being strict habitat selectors, whereas on the other side, they do so by using at least a bit of a poorer patch. The population dynamics of the competitors is analyzed using their isolegs. The isolegs allow us to deduce that the zero isoclines of the species are warped into nonlinear forms capable of producing competitive coexistence. It is shown that at the equilibrium point of this coexistence, there may be no overt competition remaining. The difficulties this presents to the field investigator are mentioned, and a modified definition of interspecific competition is suggested.

Occupational self-selection: a human capital approach to sex differences in occupational structure.

Abstract: A rich and diverse literature exists concerning the distribution of labor incomes. One approach namely that of human capital concentrates on lifetime accumulation paths of "earnings capacity units" (human capital). Individual variations in human capital imply differences in earnings power thereby yielding strong implications concerning earnings distribution within a population. Despite its explanatory power the human capital model has been widely criticized. One criticism centers on its inability to obtain inferences concerning occupational distribution. The purpose of this paper is to alleviate at least some such criticism by applying the hedonic price approach so as to embed occupational choice into the human capital framework. The significance is that neoclassical economic theory can be used to obtain implications concerning the determinants of occupational structure. (excerpt)

Intertidal Landscapes: Disturbance and the Dynamics of Pattern

Abstract: The mussel Mytilus californianus is a competitive dominant on wave—swept rocky intertidal shores. Mussel beds may exist as extensive monocultures; more often they are an everchanging mosaic of many species which inhabit wave—generated patches or gaps. This paper describes observations and experiments designed to measure the critical parameters of a model of patch birth and death, and to use the model to predict the spatial structure of mussel beds. Most measurements were made at Tatoosh Island, Washington, USA, from 1970—1979. Patch size ranged at birth from a single mussel to 38 m2; the distribution of patch sizes approximates the lognormal. Birth rates varied seasonally and regionally. At Tatoosh the rate of patch formation varied during six winters from 0.4—5.4% of the mussels removed per month. The disturbance regime during the summer and at two mainland sites was 5—10 times less. Annual disturbance patterns tended to be synchronous within 11 sites on one face of Tatoosh over a 10—yr interval, and over larger distances (16 km) along the coastline. The pattern was asynchronous, however, among four Tatoosh localities. Patch birth rate, and mean and maximum size at birth can be used as adequate indices of disturbance. Patch disappearance (death) occurs by three mechanisms. Very small patches disappear almost immediately due to a leaning response of the border mussels (0.2 cm/d). Intermediate—sized patches (<3.0 m2) are eventually obliterated by lateral movement of the peripheral mussels: estimates based on 94 experimental patches yield a mean shrinking rate of 0.05 cm/d from each of two principal dimensions. Depth of the adjacent mussel bed accounts for much of the local variation in closing rate. In very large patches, mussels must recruit as larvae from the plankton. Recovery begins at an average patch age of 26 mo; rate of space occupation, primarily due to individual growth, is 2.0—2.5%/mo. Winter birth rates suggest a mean turnover time (rotation period) for mussel beds varying from 8.1—34.7 yr, depending on the location. The minimal value is in close agreement with both observed and calculated minimal recovery times. Projections of total patch area, based on the model, are accurate to within 5% of the observed. Using a method for determining the age of patches, based on a growth curve of the barnacle Balanus cariosus, the model permits predictions of the age—size structure of the patch population. The model predicts with excellent resolution the distribution of patch area in relation to time since last disturbance. The most detailed models which include size structure within age categories are inconclusive due to small sample size. Predictions are food for large patches, the major determinants of environmental patterns, but cannot deal adequately with smaller patches because of stochastic effects. Colonization data are given in relation to patch age, size and intertidal position. We suggest that the reproductive season of certain long—lived, patch—dependent species is moulded by the disturbance regime. The necessary and vital connection between disturbance which generates spatial pattern and species richness in communities open to invasion is discussed.

The Mathematical Experience

Abstract: Winner of the 1983 National Book Award! "...a perfectly marvelous book about the Queen of Sciences, from which one will get a real feeling for what mathematicians do and who they are. The exposition is clear and full of wit and humor..." - The New Yorker (1983 National Book Award edition) Mathematics has been a human activity for thousands of years. Yet only a few people from the vast population of users are professional mathematicians, who create, teach, foster, and apply it in a variety of situations. The authors of this book believe that it should be possible for these professional mathematicians to explain to non-professionals what they do, what they say they are doing, and why the world should support them at it. They also believe that mathematics should be taught to non-mathematics majors in such a way as to instill an appreciation of the power and beauty of mathematics. Many people from around the world have told the authors that they have done precisely that with the first edition and they have encouraged publication of this revised edition complete with exercises for helping students to demonstrate their understanding. This edition of the book should find a new generation of general readers and students who would like to know what mathematics is all about. It will prove invaluable as a course text for a general mathematics appreciation course, one in which the student can combine an appreciation for the esthetics with some satisfying and revealing applications. The text is ideal for 1) a GE course for Liberal Arts students 2) a Capstone course for perspective teachers 3) a writing course for mathematics teachers. A wealth of customizable online course materials for the book can be obtained from Elena Anne Marchisotto (elena.marchisotto@csun.edu) upon request.

Skepticism towards santa rosalia, or why are there so few kinds of animals?

Abstract: In a classic paper, Hutchinson (1959) set the tone for much of the ecological work done during the past 20 years by suggesting that ecologists try to explain the numbers of species of animals. Hutchinson's approach was ecological, explaining diversity by explaining how the species could coexist. There can be little question that competitive exclusion sets an upper limit on species diversity, but it is not obvious that this upper limit will be achieved. There may be additional constraints on the process of speciation, constraints set by genetics rather than ecology. It has been usual for evolutionists to reject the possibility of sympatric speciation, and this amounts to asserting the existence of such genetic constraints. Even if the ecological opportunity for coexistence is present, under the conventional view lack of geographic isolation can prevent speciation. The attempt by Rosenzweig (1975) to give a comprehensive explanation of continental species diversity takes as its starting point the assumption that geographic isolation is a necessary prerequisite to species formation. A number of workers have made and analyzed detailed population genetic models of sympatric or parapatric speciation, in particular Maynard Smith (1966), Dickinson and Antonovics (1973), and Caisse and Antonovics (1978). Balkau and Feldman (1973) made a model of migration modification which can also be regarded as a model of parapatric speciation. The upshot of these models is that it is not difficult for sympatric speciation to occur. While these authors have largely been concerned with showing that sym-

Performance Hypothesis Testing with the Sharpe and Treynor Measures

Abstract: Asymptotic distributions of the estimators of the Sharpe and Treynor performance measures are derived. Multivariate performance comparison measures, based on the traditional Sharpe and Treynor measures, are developed with their corresponding asymptotic distributions. The behavior of these new performance measures are evaluated in small samples. For single comparisons, a Sharpe z statistic is well behaved and for multiple comparisons a Sharpe chi-square statistic is reasonably well behaved. The powers of the tests are quite sensitive to the population coefficients of variation. Multivariate test statistics based upon the Treynor measure were not very satisfactory. THIS STUDY DEVELOPS SIGNIFICANCE tests of portfolio performance utilizing the Sharpe and Treynor measures. The approximate bias and asymptotic distributions of the estimators of the traditional Sharpe and Treynor performance measures are derived. Multivariate performance comparison measures based on these traditional measures are proposed for comparing the performance of n portfolios. The approximate bias and asymptotic distributions of the multivariate comparison measures are then derived and test statistics proposed. The behavior and usefulness of the statistics for hypothesis testing are evaluated in small samples with simulation experiments. We find that for single comparisons a z statistic based on Sharpe's measure is well behaved at small sample sizes although its power in detecting typical differences with monthly data is small. The z statistic, based on the Treynor measure, is not well behaved in small samples and also lacks power. For multiple comparisons a chi-square statistic, obtained from the Sharpe measures, is reasonably well behaved at small samples and its power increases as the number of portfolios increases and/or the coefficients of variation decrease. A chi-square statistic derived from the Treynor measure is not so well behaved. Section I of the paper discusses the availability of test statistics for various classes of performance measures. It also discusses the use of the Sharpe and Treynor statistics in light of certain undesirable properties they possess and the section concludes with a brief literature survey. Section II derives the performance measure moments, asymptotic distributions, and proposed test statistics. Section III contains the results and conclusions of the univariate and multivariate simul-ations.

Origins of Human Competence: A Cultural-Ecological Perspective.

Abstract: OGBU, JOHN U. Origins of Human Competence: A Cultural-Ecological Perspective. CHILD DEVELOPMENT, 1981, 52, 413-429. In this essay it is argued that child rearing in the family and similar micro settings in the early years of life and subsequent adolescent socialization are geared toward the development of instrumental competencies required for adult economic, political, and social roles. These cultural imperatives vary from 1 cultural group to another as do the required competencies. In the United States they are different for the white middle class and for minority groups like urban ghetto blacks. It follows that the conventional research approach which used white middle-class child-rearing practices and children's competencies as standards is not useful in understanding minority groups' child rearing and competencies. Rather, for cross-cultural research, a cultural-ecological model is proposed which is not ethnocentric and studies competence in the context of the cultural imperatives in a given population. Cross-cultural or intergroup comparison is appropriate if based on data from such contextual studies.

An optical classification of coastal and oceanic waters based on the specific spectral absorption curves of phytoplankton pigments, dissolved organic matter, and other particulate materials1

Abstract: The variations of the spectral absorption coefficient of seawater can be attributed to three principal factors—phytoplankton, nonchlorophyllous particles, and yellow substances— whose concentrations are represented in this study in terms of chlorophyll a and pheophytin a content (C), the total scattering coefficient (b), and the absorption by filtered seawater at a given wavelength (Y). By assuming an exponential absorption by yellow substances, we developed a new iterative method for identifying the in situ apparent specific spectral absorption curves of the other two factors. The weighting coefficients for each of the three components are calculated for over 80 spectral absorption measurements from different representative marine regions. The reconstruction of spectral absorption curves from the three coefficients and the three specific absorption curves fits the original data with an overall average error of 3%. Relationships between these coefficients and C, b, and Y are examined. Results show that, though the spectral form of absorption by pigments can be considered as more or less invariant, the absorption “efficiency” per unit C depends on the nature of the water, and hence on the type of phytoplankton population considered. An optical classification based on the three optical coefficients related to three absorbing agents is proposed.

The Emergence of Cooperation among Egoists

Abstract: This article investigates the conditions under which cooperation will emerge in a world of egoists without central authority. This problem plays an important role in such diverse fields as political philosophy, international politics, and economic and social exchange. The problem is formalized as an iterated Prisoner's Dilemma with pairwise interaction among a population of individuals.Results from three approaches are reported: the tournament approach, the ecological approach, and the evolutionary approach. The evolutionary approach is the most general since all possible strategies can be taken into account. A series of theorems is presented which show: (1) the conditions under which no strategy can do any better than the population average if the others are using the reciprocal cooperation strategy of TIT FOR TAT, (2) the necessary and sufficient conditions for a strategy to be collectively stable, and (3) how cooperation can emerge from a small cluster of discriminating individuals even when everyone else is using a strategy of unconditional defection.