Experimental investigations in combining primal dual interior point method and simplex based LP solvers

The use of a primal dual interior point method (PD) based optimizer as a robust linear programming (LP) solver is now well established. Instead of replacing the sparse simplex algorithm (SSX), the PD is increasingly seen as complementing it. The progress of PD iterations is not hindered by the degeneracy or the stalling problem of the SSX, indeed it reaches the 'near optimum' solution very quickly. The SSX algorithm, in contrast, is not affected by the boundary conditions which slow down the convergence of the PD. If the solution to the LP problem is non unique, the PD algorithm converges to an interior point of the solution set while the SSX algorithm finds an extreme point solution. To take advantage of the attractive properties of both the PD and the SSX, we have designed a hybrid framework whereby cross over from PD to SSX can take place at any stage of the PD optimization run. The cross over to SSX involves the partition of the PD solution set to active and dormant variables. In this paper we examine the practical difficulties in partitioning the solution set, we discuss the reliability of predicting the solution set partition before optimality is reached and report the results of combining exact and inexact prediction with SSX basis recovery

A likelihood-based analysis for relaxing the exclusion restriction in randomized experiments with imperfect compliance

This paper examines the problem of relaxing the exclusion restriction for the evaluation of causal effects in randomized experiments with imperfect compliance. Exclusion restriction is a relevant assumption for identifying causal effects by the nonparametric instrumental variables technique, in which the template of a randomized experiment with imperfect compliance represents a natural parametric extension. However, the full relaxation of the exclusion restriction yields likelihood functions characterized by the presence of mixtures of distributions. This complicates a likelihood-based analysis because it implies partially identified models and more than one maximum likelihood point. We consider the model identifiability when the outcome distributions of various compliance states are in the same parametric class. A two-step estimation procedure based on detecting the root closest to the method of moments estimate of the parameter vector is proposed and analyzed in detail under normally distributed outcomes. An economic example with real data on return to schooling concludes the paper.compliers, exclusion restriction, mixture distributions, return to schooling.

Monitoring of water quality from roof runoff: Interpretation using multivariate analysis

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Temperature, pH, conductivity, colour, turbidity, anions, cations, alkalinity, total hardness and total organic carbon were screened using standard analytical techniques. Total flora at 22°C and 36°C, total coliforms, Escherichia coli and enterococci were analysed. Overall, the collected rainwater had good physicochemical quality but did not meet the requirements for drinking water. The stored rainwater is characterised by low conductivity, hardness and alkalinity compared to mains water. Three widely used bacterial indicators - total coliforms, E. coli and enterococci - were detected in the majority of samples, indicating microbiological contamination of the water. To elucidate factors affecting the rainwater composition, principal component analysis and cluster analysis were applied to the complete data set of 50 observations. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. Escherichia coli and enterococci occurred simultaneously, and their presence was linked to precipitation. Runoff quality is also unpredictable because it is sensitive to the weather. Cluster analysis differentiated three clusters: ionic composition, parameters linked with the microbiological load and indicators of faecal contamination. In future surveys, parameters from these three groups will be simultaneously monitored to more accurately characterise roof collected rainwater

A chronology of turning points in economic activity: Spain 1850-2011

This paper codifies in a systematic and transparent way a historical chronology of business cycle turning points for Spain reaching back to 1850 at annual frequency, and 1939 at monthly frequency. Such an exercise would be incomplete without assessing the new chronology itself and against others —this we do with modern statistical tools of signal detection theory. We also use these tools to determine which of several existing economic activity indexes provide a better signal on the underlying state of the economy. We conclude by evaluating candidate leading indicators and hence construct recession probability forecasts up to 12 months in the future.Business cycles ; Spain

Economic Valuation of Environmental Benefits and the Targeting of Conservation Programs: The Case of the CRP

The range of environmental problems confronting agriculture has expanded in recent years. As the largest program designed to mitigate the negative environmental effects of agriculture, the Conservation Reserve Program (CRP) has broadened its initial focus on reductions in soil erosion to consider other landscape factors that may also be beneficial. For example, preserving habitats can help protect wildlife, thus leading to more nature-viewing opportunities. This report demonstrates how nonmarket valuation models can be used in targeting conservation programs such as the CRP.Environmental Economics and Policy,

Productivity of Household Investment in Health: The Case of Colombia

The purpose of this study is to understand how public and private investments in health in Colombia are related to future earnings of individuals. The returns to good health of individuals and the determinants of the health production function are analyzed. The magnitude of the returns to having good health status is identified through the direct effect of health variables on earnings of individuals. Regional (rural-urban) and gender aspects are considered separately. The significant IV estimates showed that one more day of disability decreased male rural earnings by 33% and female by 13%, that having a disability in a given month decreased the earnings of an urban male by 28% and by 14% for an urban female, and that having one more centimeter of stature increased urban female earnings by 6. 9% and urban male earnings by 8%. These returns to height are much larger than those found in other countries and reveal that investments in nutrition are as important as investments in education for future increases in productivity and growth. Estimations of health production functions showed that it would be desirable to increase social security coverage in rural areas in order to see a lower incidence or duration of illness in these regions. However, in urban areas, where the system of social security is more developed, social security may increase the tendency to report illness. In general, wealthier individuals tend to have better health and the interaction between non-labor income of the individual and adequate housing affects positively the health status of individuals. Policies oriented to increase the coverage of basic services in households, such as electricity, potable water or sewage, have a negligible effect on height and, through height, on productivity. Policies oriented to provide more adequate housing translate into better health conditions and productivity for individuals.

Income and Child Development

We examine how income influences pre-school children’s cognitive and behavioral development, using new data from a birth cohort study of children born at the end of the 20th century. On average, low income children have lower PPVT scores, more mother-reported aggressive, withdrawn, and anxious behavior problems, and also more interviewer-reported problems with behavior, than more affluent children. For most outcomes, differences in the home environments are sufficient to explain the link between low income and poorer child outcomes. Policy simulations indicate that income transfers can potentially play an important role in reducing gaps in development between poorer and richer children.