Fronts from complex two-dimensional dispersal kernels: theory and application to Reid's paradox

Bimodal dispersal probability distributions with characteristic distances differing by several orders of magnitude have been derived and favorably compared to observations by Nathan [Nature (London) 418, 409 (2002)]. For such bimodal kernels, we show that two-dimensional molecular dynamics computer simulations are unable to yield accurate front speeds. Analytically, the usual continuous-space random walks (CSRWs) are applied to two dimensions. We also introduce discrete-space random walks and use them to check the CSRW results (because of the inefficiency of the numerical simulations). The physical results reported are shown to predict front speeds high enough to possibly explain Reid's paradox of rapid tree migration. We also show that, for a time-ordered evolution equation, fronts are always slower in two dimensions than in one dimension and that this difference is important both for unimodal and for bimodal kernels

Information provision and information needs in adult survivors of childhood cancer.

BACKGROUND: Knowledge about their past medical history is central for childhood cancer survivors to ensure informed decisions in their health management. Knowledge about information provision and information needs in this population is still scarce. We thus aimed to assess: (1) the information survivors reported to have received on disease, treatment, follow-up, and late effects; (2) their information needs in these four domains and the format in which they would like it provided; (3) the association with psychological distress and quality of life (QoL). PROCEDURE: As part of the Follow-up survey of the Swiss Childhood Cancer Survivor Study, we sent a questionnaire to all survivors (≥18 years) who previously participated to the baseline survey, were diagnosed with cancer after 1990 at an age of <16 years. RESULTS: Most survivors had received oral information only (on illness: oral: 82%, written: 38%, treatment: oral: 79%, written: 36%; follow-up: oral: 77%, written: 23%; late effects: oral: 68%, written: 14%). Most survivors who had not previously received any information rated it as important, especially information on late effects (71%). A large proportion of survivors reported current information needs and would like to receive personalized information especially on late effects (44%). Survivors with higher information needs reported higher psychological distress and lower QoL. CONCLUSIONS: Survivors want to be more informed especially on possible late effects, and want to receive personalized information. Improving information provision, both qualitatively and quantitatively, will allow survivors to have better control of their health and to become better decision makers.

Capital, Wages, and Growth: Theory and Evidence

Returns to scale to capital and the strength of capital externalities play a key role for the empirical predictions and policy implications of different growth theories. We show that both can be identified with individual wage data and implement our approach at the city-level using US Census data on individuals in 173 cities for 1970, 1980, and 1990. Estimation takes into account fixed effects, endogeneity of capital accumulation, and measurement error. We find no evidence for human or physical capital externalities and decreasing aggregate returns to capital. Returns to scale to physical and human capital are around 80 percent. We also find strong complementarities between human capital and labor and substantial total employment externalities.

Social Security in Theory and Practice (II): Efficiency Theories, Narrative Theories, and Implications for Reform

166 countries have some kind of public old age pension. What economic forces create and sustain old age Social Security as a public program? Mulligan and Sala-i-Martin (1999b) document several of the internationally and historically common features of social security programs, and explore "political" theories of Social Security. This paper discusses the "efficiency theories", which view creation of the SS program as a full of partial solution to some market failure. Efficiency explanations of social security include the "SS as welfare for the elderly" the "retirement increases productivity to optimally manage human capital externalities", "optimal retirement insurance", the "prodigal father problem", the "misguided Keynesian", the "optimal longevity insurance", the "government economizing transaction costs", and the "return on human capital investment". We also analyze four "narrative" theories of social security: the "chain letter theory", the "lump of labor theory", the "monopoly capitalism theory", and the "Sub-but-Nearly-Optimal policy response to private pensions theory". The political and efficiency explanations are compared with the international and historical facts and used to derive implications for replacing the typical pay-as-you-go system with a forced savings plan. Most of the explanations suggest that forced savings does not increase welfare, and may decrease it.

Activity assays and immunoassays for plasma Renin and prorenin: information provided and precautions necessary for accurate measurement.

BACKGROUND: Measurement of plasma renin is important for the clinical assessment of hypertensive patients. The most common methods for measuring plasma renin are the plasma renin activity (PRA) assay and the renin immunoassay. The clinical application of renin inhibitor therapy has thrown into focus the differences in information provided by activity assays and immunoassays for renin and prorenin measurement and has drawn attention to the need for precautions to ensure their accurate measurement. CONTENT: Renin activity assays and immunoassays provide related but different information. Whereas activity assays measure only active renin, immunoassays measure both active and inhibited renin. Particular care must be taken in the collection and processing of blood samples and in the performance of these assays to avoid errors in renin measurement. Both activity assays and immunoassays are susceptible to renin overestimation due to prorenin activation. In addition, activity assays performed with peptidase inhibitors may overestimate the degree of inhibition of PRA by renin inhibitor therapy. Moreover, immunoassays may overestimate the reactive increase in plasma renin concentration in response to renin inhibitor therapy, owing to the inhibitor promoting conversion of prorenin to an open conformation that is recognized by renin immunoassays. CONCLUSIONS: The successful application of renin assays to patient care requires that the clinician and the clinical chemist understand the information provided by these assays and of the precautions necessary to ensure their accuracy.

Capital, wages and growth: Theory and evidence

Returns to scale to capital and the strength of capital externalities play a key role for the empirical predictions and policy implications of different growth theories. We show that both can be identified with individual wage data and implement our approach at the city-level using US Census data on individuals in 173 cities for 1970, 1980, and 1990. Estimation takes into account fixed effects, endogeneity of capital accumulation, and measurement error. We find no evidence for human or physical capital externalities and decreasing aggregate returns to capital. Returns to scale to physical and human capital are around 80 percent. We also find strong complementarities between human capital and labor and substantial total employment externalities.

The role of awareness, information gathering and processing in school choice

This paper studies the determinants of school choice, focusing on the role of information. Weconsider how parents' search efforts and their capacity to process information (i.e., tocorrectly assess schools) affect the quality of the schools they choose for their children. Usinga novel dataset, we are able to identify parents' awareness of schools in their neighborhoodand measure their capacity to rank the quality of the school with respect to the officialrankings. We find that parents education and wealth are important factors in determiningtheir level of school awareness and information gathering. Moreover, these search effortshave important consequences in terms of the quality of school choice.

Information revelation and market incompleteness

\documentstyle[portada,11pt]{article}This paper shows that the presence of private information in aneconomy can be a source of market incompleteness even when it is feasibleto issue a set of securities that completely eliminates the informationalasymmetries in equilibrium. We analyze a simple security design model in which avolume maximizing futures exchange chooses not only the characteristics ofeach individual contract but also the number of contracts. Agents have rationalexpectations and differ in information, endowments and, possibly, attitudestoward risk. The emergence of complete or incomplete markets in equilibriumdepends on whether the {\it adverse selection effect} is stronger or weakerthan the {\it Hirshleifer effect}, as new securitiesare issued and prices reveal more information. When the Hirshleifer effectdominates, the exchange chooses an incomplete set of financial contracts, andthe equilibrium price is partially revealing.

Information acquisition and entry

Before firms decide whether to enter a new market or not, they havethe opportunity to buy information about several variables that might affectthe profitability of this market. Our model differs from the existing literatureon endogenous information acquisition in two respects: (1) there is uncertaintyabout more than one variable, and (2) information is acquired secretly. Whenthe cost of acquiring information is small, entry decisions will be as ifthere was perfect information. Equilibria where each firm acquires only asmall amount of information are more robust than the socially undesirableequilibria where all firms gather all information. Examples illustrate theimportance of assumptions (1) and (2).

The optimum quantity of money: Theory and evidence

In this paper we propose a simple and general model for computing the Ramsey optimal inflation tax, which includes several models from the previous literature as special cases. We show that it cannot be claimed that the Friedman rule is always optimal (or always non--optimal) on theoretical grounds. The Friedman rule is optimal or not, depending on conditions related to the shape of various relevant functions. One contribution of this paper is to relate these conditions to {\it measurable} variables such as the interest rate or the consumption elasticity of money demand. We find that it tends to be optimal to tax money when there are economies of scale in the demand for money (the scale elasticity is smaller than one) and/or when money is required for the payment of consumption or wage taxes. We find that it tends to be optimal to tax money more heavily when the interest elasticity of money demand is small. We present empirical evidence on the parameters that determine the optimal inflation tax. Calibrating the model to a variety of empirical studies yields a optimal nominal interest rate of less than 1\%/year, although that finding is sensitive to the calibration.

Social security in theory and practice (II): Efficiency theories, narrative theories and implications for reform

166 countries have some kind of public old age pension. What economic forcescreate and sustain old age Social Security as a public program? Mulligan and Sala-i-Martin (1999b) document several of the internationally and historically common features of social security programs, and explore "political" theories of Social Security. This paper discusses the "efficiency theories", which view creation of the SS program as a full of partial solution to some market failure. Efficiency explanations of social security include the "SS as welfare for the elderly" the "retirement increases productivity to optimally manage human capital externalities", "optimal retirement insurance", the "prodigal father problem", the "misguided Keynesian", the "optimal longevity insurance", the "governmenteconomizing transaction costs", and the "return on human capital investment". We also analyze four "narrative" theories of social security: the "chain letter theory", the "lump of labor theory", the "monopoly capitalism theory", and the "Sub-but-Nearly-Optimal policy response to private pensions theory".The political and efficiency explanations are compared with the international and historical facts and used to derive implications for replacing the typical pay-as-you-go system with a forced savings plan. Most of the explanations suggest that forced savings does not increase welfare, and may decrease it.