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Uncertainty
Kinds of Uncertainty Terms modified by Uncertainty Selected AbstractsDEMAND UNCERTAINTY AND RESALE PRICE MAINTENANCECONTEMPORARY ECONOMIC POLICY, Issue 4 2000D FLATH When retailers must commit to shipment quantities prior to resolution of demand uncertainty, manufacturer stipulation of a minimum retail price is likely to be profitable for the manufacturer and not damaging to the retailers. The reason is simple: if demand turns out to be low, the unfettered market-clearing price can lie below the price that maximizes total sales revenue. A minimum retail price that is binding in the low-demand state can thus increase total revenue even though it saddles retailers with unsold merchandise. The ubiquity of full reimbursement for returns in Japan, even though it is in theory merely a second-best way of achieving minimum retail price stipulations, reveals important aspects of manufacturer maintenance of retail prices having to do with enforcement problems, the allocation of risk-bearing, and economic incentives. These aspects of resale price maintenance (RPM) are relevant to the normative evaluation of the special exemptions for RPM that Japan's Fair Trade Commission has long maintained but is now phasing out. [source] UNCERTAINTY AND MONETARY POLICY RULES IN THE UNITED STATESECONOMIC INQUIRY, Issue 2 2009CHRISTOPHER MARTIN This article analyzes the impact of uncertainty about the true state of the economy on monetary policy rules in the United States since the early 1980s. Extending the Taylor rule to allow for this type of uncertainty, we find evidence that the predictions of the theoretical literature on responses to uncertainty are reflected in the behavior of policymakers, suggesting that policymakers are adhering to prescriptions for optimal policy. Our estimates suggest that the effect of uncertainty on interest rates was most marked in 1983, when uncertainty increased interest rates by up to 140 basis points, in 1990,1991, when uncertainty reduced interest rates by up to 80 basis points, and in 1996,2001, when uncertainty reduced interest rates by up to 70 basis points over 5 yr. (JEL C51, C52, E52, E58) [source] THE EFFECTS OF UNCERTAINTY ON THE LEVERAGE OF NONFINANCIAL FIRMSECONOMIC INQUIRY, Issue 2 2009CHRISTOPHER F. BAUM This paper investigates the link between the optimal level of nonfinancial firms' short-term leverage and macroeconomic and idiosyncratic sources of uncertainty. We develop a structural model of a firm's value maximization problem that predicts a negative relationship between uncertainty and optimal levels of borrowing. This proposition is tested using a panel of nonfinancial U.S. firms drawn from the COMPUSTAT quarterly database covering the period 1993,2003. The estimates confirm that as either form of uncertainty increases, firms decrease their levels of short-term leverage. This effect is stronger for macroeconomic uncertainty than for idiosyncratic uncertainty. (JEL C23, D8, D92, G32) [source] RATIONAL PARTISAN THEORY, UNCERTAINTY, AND SPATIAL VOTING: EVIDENCE FOR THE BANK OF ENGLAND'S MPCECONOMICS & POLITICS, Issue 2 2010ARNAB BHATTACHARJEE The transparency and openness of the monetary policy-making process at the Bank of England has provided very detailed information on both the decisions of individual members of the Monetary Policy Committee (MPC) and the information on which they are based. In this paper, we consider this decision-making process in the context of a model in which inflation forecast targeting is used, but there is heterogeneity among the members of the committee. We find that rational partisan theory can explain spatial voting behavior under forecast uncertainty about the output gap. Internally generated forecasts of output and market-generated expectations of medium-term inflation provide the best description of discrete changes in interest rates, in combination with uncertainty in the macroeconomic environment. There is also a role for developments in asset, housing and labor markets. Further, spatial voting patterns clearly differentiate between internally and externally apzpointed members of the MPC. The results have important implications for committee design and the conduct of monetary policy. [source] POLICY UNCERTAINTY, ELECTORAL SECURITIES, AND REDISTRIBUTION,INTERNATIONAL ECONOMIC REVIEW, Issue 1 2010Andrea Mattozzi This article investigates how uncertainty about the adoption of a redistribution policy affects political support for redistribution when individuals can trade policy-contingent securities in the stock market. In equilibrium the support for redistribution is smaller than where no "policy-insurance market" is available. This implies that in economies with well-developed financial markets redistribution decreases with the level of participation in these markets and with income inequality. Furthermore, the existence of a policy-insurance market may lead to a less equal distribution of income than where no insurance is available even if a majority of individuals are redistributing resources through private transfers. [source] MODEL UNCERTAINTY AND ITS IMPACT ON THE PRICING OF DERIVATIVE INSTRUMENTSMATHEMATICAL FINANCE, Issue 3 2006Rama Cont Uncertainty on the choice of an option pricing model can lead to "model risk" in the valuation of portfolios of options. After discussing some properties which a quantitative measure of model uncertainty should verify in order to be useful and relevant in the context of risk management of derivative instruments, we introduce a quantitative framework for measuring model uncertainty in the context of derivative pricing. Two methods are proposed: the first method is based on a coherent risk measure compatible with market prices of derivatives, while the second method is based on a convex risk measure. Our measures of model risk lead to a premium for model uncertainty which is comparable to other risk measures and compatible with observations of market prices of a set of benchmark derivatives. Finally, we discuss some implications for the management of "model risk." [source] COURNOT OLIGOPOLY UNDER STRATEGIC UNCERTAINTY WITH OPTIMISTIC AND PESSIMISTIC FIRMSMETROECONOMICA, Issue 3 2005Fulvio Fontini ABSTRACT In this paper the Cournot oligopoly under uncertainty is analyzed by means of the Choquet Expected Utility (CEU) theory. Firms are supposed to be either optimistic (CEU maximizers who hold concave capacities) or pessimistic (convex capacities). Reaction functions, equilibrium quantities, prices and profits are derived and compared for different degrees of uncertainty and uncertainty attitude (optimism or pessimism). It is proved that optimists make higher profits than pessimists whenever uncertainty is sufficiently low. If it is high just optimists participate in the market making losses. An interpretation of the main results in terms of the market's level of maturity is provided. [source] SUSTAINABLE YIELDS IN FISHERIES: UNCERTAINTY, RISK-AVERSION, AND MEAN-VARIANCE ANALYSISNATURAL RESOURCE MODELING, Issue 3 2010CHRISTIAN-OLIVER EWALD Abstract We consider a model of a fishery in which the dynamics of the unharvested fish population are given by the stochastic logistic growth equation Similar to the classical deterministic analogon, we assume that the fishery harvests the fish population following a constant effort strategy. In the first step, we derive the effort level that leads to maximum expected sustainable yield, which is understood as the expectation of the equilibrium distribution of the stochastic dynamics. This replaces the nonzero fixed point in the classical deterministic setup. In the second step, we assume that the fishery is risk averse and that there is a tradeoff between expected sustainable yield and uncertainty measured in terms of the variance of the equilibrium distribution. We derive the optimal constant effort harvesting strategy for this problem. In the final step, we consider an approach that we call the mean-variance analysis to sustainable fisheries. Similar as in the now classical mean-variance analysis in finance, going back to Markowitz [1952], we study the problem of maximizing expected sustainable yields under variance constraints, and with this, minimizing the variance, e.g., risk, under guaranteed minimum expected sustainable yields. We derive explicit formulas for the optimal fishing effort in all four problems considered and study the effects of uncertainty, risk aversion, and mean reversion speed on fishing efforts. [source] GROWTH AND MEASUREMENT UNCERTAINTY IN AN UNREGULATED FISHERYNATURAL RESOURCE MODELING, Issue 3 2009ANNE B. JOHANNESEN Abstract Complete information is usually assumed in harvesting models of marine and terrestrial resources. In reality, however, complete information never exists. Fish and wildlife populations often fluctuate unpredictably in numbers, and measurement problems are frequent. In this paper, we analyze a time-discrete fishery model that distinguishes between uncertain natural growth and measurement error and in which exploitation takes place in an unregulated manner. Depending on the parameterization of the model and at which point of time uncertainty is resolved, it is shown that expected harvest under ecological uncertainty may be below or above that of the benchmark model with no uncertainty. On the other hand, when stock measurement is uncertain, expected harvest never exceeds the benchmark level. We also demonstrate that the harvesting profit, or rent, under uncertainty may be above that of the benchmark situation of complete information. In other words, less information may be beneficial for the fishermen. [source] OUTPUT VERSUS INPUT CONTROLS UNDER UNCERTAINTY: THE CASE OF A FISHERYNATURAL RESOURCE MODELING, Issue 2 2009SATOSHI YAMAZAKI Abstract The paper compares the management outcomes with a total allowable catch (TAC) and a total allowable effort (TAE) in a fishery under uncertainty. Using a dynamic programming model with multiple uncertainties and estimated growth, harvest, and effort functions from one of the world's largest fisheries, the relative economic and biological benefits of a TAC and TAE are compared and contrasted in a stochastic environment. This approach provides a decision and modeling framework to compare instruments and achieve desired management goals. A key finding is that neither instrument is always preferred in a world of uncertainty and that regulator's risk aversion and weighting in terms of expected net profits and biomass, and the trade-offs in terms of expected values and variance determine instrument choice. [source] SWITCHING TO A TEMPORARY CALL AUCTION IN TIMES OF HIGH UNCERTAINTYTHE JOURNAL OF FINANCIAL RESEARCH, Issue 1 2010David Abad Abstract We evaluate a stock-specific circuit breaker implemented in several European stock exchanges, which consists of a short-lived call auction triggered by intraday stock-specific price limits. It differs from U.S. trading halts in that it is short-lived and nondiscretionary, and a trading mechanism (continuous or discrete) is always going. It differs from daily price limits in that trade prices are not restricted once the limit is hit. Intraday price ranges are smaller and adjusted to the recent volatility, so that limit hits are more frequent. We contribute to the debate about circuit breakers by enlarging the span of these mechanisms studied. [source] DOES THE MAGNITUDE OF THE EFFECT OF INFLATION UNCERTAINTY ON OUTPUT GROWTH DEPEND ON THE LEVEL OF INFLATION?THE MANCHESTER SCHOOL, Issue 2 2010KUANG-LIANG CHANG A bivariate Markov regime switching model is employed to verify whether the relationship between inflation and inflation uncertainty, or the negative effects of inflation and inflation uncertainty on output growth, vary with the level of inflation. Inflation and inflation uncertainty are positively correlated in the high-inflation regime. In contrast, in the low-inflation regime, the direct effect of inflation on output growth is insignificant, but the indirect negative effect on growth via inflation uncertainty is highly significant. The negative influence in a high-inflation regime is 2.664 times greater than that in a low-inflation regime. [source] COPING WITH UNCERTAINTY: HISTORICAL AND REAL-TIME ESTIMATES OF THE NATURAL UNEMPLOYMENT RATE AND THE UK MONETARY POLICY*THE MANCHESTER SCHOOL, Issue 4 2009GEORGE CHOULIARAKIS The paper derives and compares historical and real-time estimates of the UK natural unemployment rate and shows that real-time estimates are fraught with noise and should be treated with scepticism. A counterfactual exercise shows that, for most of the 1990s, the Bank of England tracked changes in the natural rate relatively successfully, albeit with some recognition lag which, at times, might have led to excessively cautious policy. A careful scrutiny of the minutes of the monetary policy committee meetings reveals that such ,cautiousness' should be taken as evidence of awareness of the real-time informational limitations that monetary policy is facing. [source] UNCERTAINTY, LEARNING AND GROWTHTHE MANCHESTER SCHOOL, Issue 5 2008RAGCHAASUREN GALINDEV The paper extends Blackburn and Galindev's (Economics Letters, Vol. 79 (2003), pp. 417,421) stochastic growth model in which productivity growth entails both external and internal learning behaviour with a constant relative risk aversion utility function and productivity shocks. Consequently, the relationship between long-term growth and short-term volatility depends not only on the relative importance of each learning mechanism but also on a parameter measuring individuals' attitude towards risk. [source] UNCERTAINTY AND WAGE SETTING IN A MONETARY UNION,THE MANCHESTER SCHOOL, Issue 4 2008CARSTEN HEFEKER The enlargement of the European Monetary Union is likely to lead to an increase of uncertainty about the transmission of monetary policy for the larger union. Adding new members to the central bank council in addition implies that the policy reaction of the enlarged council will be uncertain for an initial period. The paper considers the influence of both types of uncertainty on wage setting and unemployment in the larger monetary union. [source] MERGERS UNDER UNCERTAINTY: THE EFFECTS OF DEBT FINANCING,THE MANCHESTER SCHOOL, Issue 5 2007M. PILAR SOCORRO In this paper, we consider a Cournot oligopoly with demand uncertainty, fixed costs and constant marginal costs. The demand uncertainty makes some mergers that would be unprofitable in a certain environment profitable in this model. However, socially advantageous mergers may be still unprofitable for the colluding firms, so public intervention may be needed. One possibility consists in subsidizing such mergers. However, the combination of limited liability debt financing and an appropriate antitrust policy leads to higher social welfare than subsidies. The reason is that, given the limited liability effect, merging parties compete more aggressively, so the reduction in market quantity is mitigated. [source] THE CHOICE OF CAPACITY IN MIXED DUOPOLY UNDER DEMAND UNCERTAINTY,THE MANCHESTER SCHOOL, Issue 3 2006YUANZHU LU We analyze the capacity choice of firms under demand uncertainty in a mixed duopoly market consisting of one private firm and one public firm. We define a two-stage game where firms choose capacity in the first stage without knowing which state of Nature is going to be realized, and output in the second stage knowing which state is realized. We address the question of maintaining over and under capacity in the equilibrium as a strategic device; and show that both symmetric and asymmetric outcomes can be realized. [source] MACROECONOMIC UNCERTAINTY AND MACROECONOMIC PERFORMANCE: ARE THEY RELATED?THE MANCHESTER SCHOOL, Issue 2005DON BREDIN We use a very general bivariate generalized autoregressive conditional heteroskedasticity-in-mean model and G7 monthly data covering the 1957,2003 period to test for the impact of real and nominal macroeconomic uncertainty on inflation and output growth. Our evidence supports a number of important conclusions. First, in most countries output growth uncertainty is a positive determinant of the output growth rate. Second, there is mixed evidence regarding the effect of inflation uncertainty on inflation and output growth. Hence, contrary to popular belief, uncertainty about the inflation rate is not necessarily detrimental to economic growth but in some cases it may also enhance growth. Finally, there is mixed evidence on the effect of output uncertainty on inflation. In sum, our results indicate that macroeconomic uncertainty may even improve macroeconomic performance. [source] ADAPTIVE SLIDING MODE BACKSTEPPING CONTROL OF NONLINEAR SYSTEMS WITH UNMATCHED UNCERTAINTYASIAN JOURNAL OF CONTROL, Issue 4 2004Ali J. Koshkouei ABSTRACT This paper considers an adaptive backstepping algorithm for designing the control for a class of nonlinear continuous uncertain processes with disturbances that can be converted to a parametric semi-strict feedback form. Sliding mode control using a combined adaptive backstepping sliding mode control (SMC) algorithm, is also studied. The algorithm follows a systematic procedure for the design of adaptive control laws for the output tracking of nonlinear systems with matched and unmatched uncertainty. [source] UNCERTAINTY AND CONSUMPTION: NEW EVIDENCE IN OECD COUNTRIESBULLETIN OF ECONOMIC RESEARCH, Issue 3 2010Mario Menegatti D91; E21 ABSTRACT This work analyses the empirical evidence about precautionary saving in OECD countries in the period 1955,2000. Unlike the previous literature, we perform the test using a measure of uncertainty allowing for heterogeneity in stochastic processes which generate data for each country and selecting for each economy the autoregressive moving average process which best describes the series. The results obtained support the main conclusion of precautionary saving theory, showing that a greater degree of uncertainty increases saving. A less clear conclusion is obtained with reference to the effect of uncertainty on consumption growth, which does not seem to be strongly supported by the data. [source] TIME-VARYING UNCERTAINTY AND THE CREDIT CHANNELBULLETIN OF ECONOMIC RESEARCH, Issue 4 2008Victor Dorofeenko E4; E5; E2 ABSTRACT We extend the Carlstrom and Fuerst (American Economic Review, 1997, 87, pp. 893,910) agency cost model of business cycles by including time-varying uncertainty in the technology shocks that affect capital production. We first demonstrate that standard linearization methods can be used to solve the model yet second moments enter the economy's equilibrium policy functions. We then demonstrate that an increase in uncertainty causes, ceteris paribus, a fall in investment supply. We also show that persistence of uncertainty affects both quantitatively and qualitatively the behaviour of the economy. [source] Evaluation of Uncertainties Associated with Geocoding TechniquesCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2004Hassan A. Karimi Geocoded data play a major role in numerous engineering applications such as transportation and environmental studies where geospatial information systems (GIS) are used for spatial modeling and analysis as they contain spatial information (e.g., latitude and longitude) about objects. The information that a GIS produces is impacted by the quality of the geocoded data (e.g., coordinates) stored in its database. To make appropriate and reasonable decisions using geocoded data, it is important to understand the sources of uncertainty in geocoding. There are two major sources of uncertainty in geocoding, one related to the database that is used as a reference data set to geocode objects and one related to the interpolation technique used. Factors such as completeness, correctness, consistency, currency, and accuracy of the data in the reference database contribute to the uncertainty of the former whereas the specific logic and assumptions used in an interpolation technique contribute to the latter. The primary purpose of this article is to understand uncertainties associated with interpolation techniques used for geocoding. In doing so, three geocoding algorithms were used and tested and the results were compared with the data collected by the Global Positioning System (GPS). The result of the overall comparison indicated no significant differences between the three algorithms. [source] Style of Knowing Regarding UncertaintiesCURRICULUM INQUIRY, Issue 1 2007DEBORAH HELSING This article addresses a key contrast in how teachers may regard the uncertainties of their work, considering how an orientation to uncertainty can be regarded as a decision-making style. Through the use of case studies, the author contrasts two teachers. One is oriented toward uncertainties in her work and describes her herself as being always "on the edge" of her capabilities, constantly seeking out perspectives that differ from and challenge her own and remaining vigilant to the need for improvising to respond to the circumstances of the moment. The other is oriented away from uncertainties and describes herself as prepared and deliberate; committed to achieving outcomes in line with her articulated goals and purposes; and purposeful about which unresolved questions she chooses to pursue. This contrast has implications not only for how these teachers make decisions and view their professional growth, but also for how some teachers may be understood, and misunderstood, by others. In a culture that often seeks to ignore pervasive moral ambiguities and focuses instead on questions for which there are easily identifiable answers (Cuban, 1992), an orientation toward uncertainty is more likely to be devalued or seen as an indication that one is not teaching well. Identifying these different approaches to decision-making styles enables us to appreciate the integrity and strength of each, as well as the limitations of each, suggesting new possibilities for research and for teachers' professional development. [source] Patient-centred and professional-directed implementation strategies for diabetes guidelines: a cluster-randomized trial-based cost-effectiveness analysisDIABETIC MEDICINE, Issue 2 2006R. F. Dijkstra Abstract Aims Economic evaluations of diabetes interventions do not usually include analyses on effects and cost of implementation strategies. This leads to optimistic cost-effectiveness estimates. This study reports empirical findings on the cost-effectiveness of two implementation strategies compared with usual hospital outpatient care. It includes both patient-related and intervention-related cost. Patients and methods In a clustered-randomized controlled trial design, 13 Dutch general hospitals were randomly assigned to a control group, a professional-directed or a patient-centred implementation programme. Professionals received feedback on baseline data, education and reminders. Patients in the patient-centred group received education and diabetes passports. A validated probabilistic Dutch diabetes model and the UKPDS risk engine are used to compute lifetime disease outcomes and cost in the three groups, including uncertainties. Results Glycated haemoglobin (HbA1c) at 1 year (the measure used to predict diabetes outcome changes over a lifetime) decreased by 0.2% in the professional-change group and by 0.3% in the patient-centred group, while it increased by 0.2% in the control group. Costs of primary implementation were < 5 Euro per head in both groups, but average lifetime costs of improved care and longer life expectancy rose by 9389 Euro and 9620 Euro, respectively. Life expectancy improved by 0.34 and 0.63 years, and quality-adjusted life years (QALY) by 0.29 and 0.59. Accordingly, the incremental cost per QALY was 32 218 Euro for professional-change care and 16 353 for patient-centred care compared with control, and 881 Euro for patient-centred vs. professional-change care. Uncertainties are presented in acceptability curves: above 65 Euro per annum the patient-directed strategy is most likely the optimum choice. Conclusion Both guideline implementation strategies in secondary care are cost-effective compared with current care, by Dutch standards, for these patients. Additional annual costs per patient using patient passports are low. This analysis supports patient involvement in diabetes in the Netherlands, and probably also in other Western European settings. [source] Bridging the gap between field data and global models: current strategies in aeolian researchEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Joanna Bullard Abstract Modern global models of earth-atmosphere-ocean processes are becoming increasingly sophisticated but still require validation against empirical data and observations. This commentary reports on international initiatives amongst aeolian researchers that seek to combine field-based data sets and geomorphological frameworks for improving the quality of data available to constrain and validate global models. These include a second iteration of the Dust Indicators and Records from Terrestrial Marine Palaeoenvironments (DIRTMAP2) database, the Digital Atlas of Sand Seas and Dunefields of the World and a new geomorphology-based land surface map produced by the QUEST (Quantifying Uncertainties in the Earth System) Working Group on Dust. Copyright © 2010 John Wiley & Sons, Ltd. [source] Seismic demand sensitivity of reinforced concrete shear-wall building using FOSM methodEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2005Tae-Hyung Lee Abstract The uncertainty in the seismic demand of a structure (referred to as the engineering demand parameter, EDP) needs to be properly characterized in performance-based earthquake engineering. Uncertainties in the ground motion and in structural properties are responsible for EDP uncertainty. In this study, sensitivity of EDPs to major uncertain variables is investigated using the first-order second-moment method for a case study building. This method is shown to be simple and efficient for estimating the sensitivity of seismic demand. The EDP uncertainty induced by each uncertain variable is used to determine which variables are most significant. Results show that the uncertainties in ground motion are more significant for global EDPs, namely peak roof acceleration and displacement, and maximum inter-storey drift ratio, than those in structural properties. Uncertainty in the intensity measure (IM) of ground motion is the dominant variable for uncertainties in local EDPs such as the curvature demand at critical cross-sections. Conditional sensitivity of global and local EDPs given IM is also estimated. It is observed that the combined effect of uncertainties in structural properties is more significant than uncertainty in ground motion profile at lower IM levels, while the opposite is true at higher IM levels. Copyright © 2005 John Wiley & Sons, Ltd. [source] Magnitude and sources of uncertainties in soil organic carbon (SOC) stock assessments at various scalesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2009E. Goidts Summary Uncertainties in soil organic carbon (SOC) stock assessments are rarely quantified even though they are critical in determining the significance of the results. Previous studies on this topic generally focused on a single variable involved in the SOC stock calculation (SOC concentration, sampling depth, bulk density and rock fragment content) or on a single scale, rather than using an integrated approach (i.e. taking into account interactions between variables). This study aims to apply such an approach to identify and quantify the uncertainties in SOC stock assessments for different scales and spatial landscape units (LSU) under agriculture. The error propagation method (, method) was used to quantify the relative contribution of each variable and interaction involved to the final SOC stock variability. Monte Carlo simulations were used to cross-check the results. Both methods converged (r2=0.78). As expected, the coefficient of variation of the SOC stock increased across scales (from 5 to 35%), and was higher for grassland than for cropland. Although the main source of uncertainty in the SOC stock varied according to the scale and the LSU considered, the variability of SOC concentration (due to errors from the laboratory and to the high SOC spatial variability) and of the rock fragment content were predominant. When assessing SOC stock at the landscape scale, one should focus on the precision of SOC analyses from the laboratory, the reduction of SOC spatial variability (using bulk samples, accurate re-sampling, high sampling density or stratified sampling), and the use of equivalent masses for SOC stock comparison. The regional SOC stock monitoring of agricultural soils in southern Belgium allows the detection of an average SOC stock change of 20% within 11 years if very high rates of SOC stock changes occur (1 t C ha,1 year,1). Amplitude et sources des incertitudes liées aux estimations des stocks de carbone organique dans le sol (COS) à différentes échelles Résumé Les erreurs associées aux estimations du stock de carbone organique dans le sol (COS) sont rarement quantifiées bien qu'elles puissent empêcher l'obtention de résultats significatifs. Les quelques études qui le font focalisent en général sur une seule variable nécessaire au calcul du stock de COS (concentration en COS, profondeur échantillonnée, densité apparente et contenu en fragments rocheux) ou sur une échelle spatiale particulière, sans utiliser d'approche intégrée (prenant en compte les interactions entre les variables). Cette étude a pour objectif d'utiliser une telle approche pour identifier et quantifier les incertitudes liées aux estimations de stock de COS à différentes échelles spatiales et pour diverses unités spatiales de paysages (USP) agricoles. La loi de propagation des erreurs (méthode ,) permet de quantifier la contribution relative de chaque variable et interaction à la variabilité finale du stock de COS. Les simulations de Monte Carlo sont utilisées pour la vérification croisée des résultats. Les deux méthodes ont convergé (r2= 0.78). Comme prévu, le coefficient de variation du stock de COS a proportionnellement augmenté avec l'échelle spatiale considérée (de 5 à 35%), et était plus élevé pour les cultures que pour les prairies. Bien que la principale source d'erreur sur le stock de COS soit fonction de l'échelle spatiale et du type d'USP considérés, la variabilité du contenu en COS (du fait des erreurs de laboratoire et de sa grande variabilité spatiale) et du contenu en fragments rocheux étaient prédominants. Lors de l'estimation des stocks de COS à l'échelle du paysage, l'attention devrait prioritairement porter sur la précision des analyses en COS du laboratoire, la réduction de la variabilité spatiale du COS (en utilisant des échantillons composites, un ré-échantillonnage précis, une densité d'échantillonnage élevée ou un échantillonnage stratifié), et sur l'utilisation de masses équivalentes pour comparer les stocks de COS. Le réseau régional de suivi des stocks de COS des sols agricoles dans le sud de la Belgique permet la détection d'un changement de stock de COS moyen de 20% en 11 ans pour un taux très élevé de changement en stock de COS (1 t C ha,1 year,1). [source] DETECTING CORRELATION BETWEEN CHARACTERS IN A COMPARATIVE ANALYSIS WITH UNCERTAIN PHYLOGENYEVOLUTION, Issue 6 2003John P. Huelsenbeck Abstract., The importance of accommodating the phylogenetic history of a group when performing a comparative analysis is now widely recognized. The typical approaches either assume the tree is known without error, or they base inferences on a collection of well-supported trees or on a collection of trees generated under a stochastic model of cladogenesis. However, these approaches do not adequately account for the uncertainty of phylogenetic trees in a comparative analysis, especially when data relevant to the phylogeny of a group are available. Here, we develop a method for performing comparative analyses that is based on an extension of Felsenstein's independent contrasts method. Uncertainties in the phylogeny, branch lengths, and other parameters are accommodated by averaging over all possible trees, weighting each by the probability that the tree is correct. We do this in a Bayesian framework and use Markov chain Monte Carlo to perform the high-dimensional summations and integrations required by the analysis. We illustrate the method using comparative characters sampled from Anolis lizards. [source] Soil organic carbon stock change due to land use activity along the agricultural frontier of the southwestern Amazon, Brazil, between 1970 and 2002GLOBAL CHANGE BIOLOGY, Issue 10 2010STOÉCIO M. F. MAIA Abstract The southwestern portion of the Brazilian Amazon arguably represents the largest agricultural frontier in the world, and within this region the states of Rondônia and Mato Grosso have about 24% and 32% of their respective areas under agricultural management, which is almost half of the total area deforested in the Brazilian Amazon biome. Consequently, it is assumed that deforestation in this region has caused substantial loss of soil organic carbon (SOC). In this study, the changes in SOC stocks due to the land use change and management in the southwestern Amazon were estimated for two time periods from 1970,1985 and 1985,2002. An uncertainty analysis was also conducted using a Monte Carlo approach. The results showed that mineral soils converted to agricultural management lost a total of 5.37 and 3.74 Tg C yr,1 between 1970,1985 and 1985,2002, respectively, along the Brazilian Agricultural Frontier in the states of Mato Grosso and Rondônia. Uncertainties in these estimates were ±37.3% and ±38.6% during the first and second time periods, respectively. The largest sources of uncertainty were associated with reference carbon (C) stocks, expert knowledge surveys about grassland condition, and the management factors for nominal and degraded grasslands. These results showed that land use change and management created a net loss of C from soils, however, the change in SOC stocks decreased substantially from the first to the second time period due to the increase in land under no-tillage. [source] Inversion of terrestrial ecosystem model parameter values against eddy covariance measurements by Monte Carlo samplingGLOBAL CHANGE BIOLOGY, Issue 8 2005Wolfgang Knorr Abstract Effective measures to counter the rising levels of carbon dioxide in the Earth's atmosphere require that we better understand the functioning of the global carbon cycle. Uncertainties about, in particular, the terrestrial carbon cycle's response to climate change remain high. We use a well-known stochastic inversion technique originally developed in nuclear physics, the Metropolis algorithm, to determine the full probability density functions (PDFs) of parameters of a terrestrial ecosystem model. By thus assimilating half-hourly eddy covariance measurements of CO2 and water fluxes, we can substantially reduce the uncertainty of approximately five model parameters, depending on prior uncertainties. Further analysis of the posterior PDF shows that almost all parameters are nearly Gaussian distributed, and reveals some distinct groups of parameters that are constrained together. We show that after assimilating only 7 days of measurements, uncertainties for net carbon uptake over 2 years for the forest site can be substantially reduced, with the median estimate in excellent agreement with measurements. [source] | |||||||||||||||||||||||||||||||||||||