Tests of Inference for Dummy Variables in Regressions with Logarithmic Transformed Dependent Variables

The interpretation of dummy variables in regressions where the dependent variable is subject to a log transformation has been of continuing interest in economics. However, in the main, these earlier papers do not deal with the inferential aspects of the parameters estimated. In this paper we compare the inference implied by the hypotheses tested on the linear parameter estimated in the model and the tests applied to the proportional change that this parameter implies. An important element in this analysis is the asymmetry introduced by the log transformation. Suggestions are made for the appropriate test procedure in this case. Examples are presented from some common econometric applications of this model in the estimation of hedonic price models and wage equations.Hypothesis tests;lognormal distribution; measures of proportional change; wage equation; hedonic price model

Clustering in a Data Envelopment Analysis Using Bootstrapped Efficiency Scores

This paper explores the insight from the application of cluster analysis to the results of a Data Envelopment Analysis of productive behaviour. Cluster analysis involves the identification of groups among a set of different objects (individuals or characteristics). This is done via the definitions of a distance matrix that defines the relationship between the different objects, which then allows the determination of which objects are most similar into clusters. In the case of DEA, cluster analysis methods can be used to determine the degree of sensitivity of the efficiency score for a particular DMU to the presence of the other DMUs in the sample that make up the reference technology to that DMU. Using the bootstrapped values of the efficiency measures we construct two types of distance matrices. One is defined as a function of the variance covariance matrix of the scores with respect to each other. This implies that the covariance of the score of one DMU is used as a measure of the degree to which the efficiency measure for a single DMU is influenced by the efficiency level of another. An alternative distance measure is defined as a function of the ranks of the bootstrapped efficiency. An example is provided using both measures as the clustering distance for both a one input one output case and a two input two output case.

Inferences for the Extremum of Quadratic Regression Models

Quadratic functions are often used in regression to infer the existence of an extremum in a relationship although tests of the location of the extremum are rarely performed. We investigate the construction of the following confidence intervals: Delta, Fieller, estimated first derivative, bootstrapping, Bayesian and likelihood ratio. We propose interpretations for the unbounded intervals that may be generated by some of these methods. The coverage of the confidence intervals is assessed by Monte Carlo; the Delta and studentized bootstrap can perform quite poorly. Of all the methods, the first derivative method is easiest to implement.Inverted U-Shaped, turning point, Fieller method, Delta method, 1st derivative function, Bayesian, Likelihood ratio, Bootstrap.

A Model of Relative Price Elasticities from Second Moments of Demand

The first of two papers delivered at the joint SEEC/BIEE Energy Modelling Group seminar on 6 May 1994 at the University of Surrey

End Use Elasticities

The second of two papers delivered at the joint SEEC/BIEE Energy Modelling Group seminar on 6 May 1994 at the University of Surrey

New Insights into Metabolic Properties of Marine Bacteria Encoding Proteorhodopsins

Proteorhodopsin phototrophy was recently discovered in oceanic surface waters. In an effort to characterize uncultured proteorhodopsin-exploiting bacteria, large-insert bacterial artificial chromosome (BAC) libraries from the Mediterranean Sea and Red Sea were analyzed. Fifty-five BACs carried diverse proteorhodopsin genes, and we confirmed the function of five. We calculate that proteorhodopsin-exploiting bacteria account for 13% of microorganisms in the photic zone. We further show that some proteorhodopsin-containing bacteria possess a retinal biosynthetic pathway and a reverse sulfite reductase operon, employed by prokaryotes oxidizing sulfur compounds. Thus, these novel phototrophs are an unexpectedly large and metabolically diverse component of the marine microbial surface water

Transcriptome Alteration in the Diabetic Heart by Rosiglitazone: Implications for Cardiovascular Mortality

BACKGROUND: Recently, the type 2 diabetes medication, rosiglitazone, has come under scrutiny for possibly increasing the risk of cardiac disease and death. To investigate the effects of rosiglitazone on the diabetic heart, we performed cardiac transcriptional profiling and imaging studies of a murine model of type 2 diabetes, the C57BL/KLS-lepr(db)/lepr(db) (db/db) mouse. METHODS AND FINDINGS: We compared cardiac gene expression profiles from three groups: untreated db/db mice, db/db mice after rosiglitazone treatment, and non-diabetic db/+ mice. Prior to sacrifice, we also performed cardiac magnetic resonance (CMR) and echocardiography. As expected, overall the db/db gene expression signature was markedly different from control, but to our surprise was not significantly reversed with rosiglitazone. In particular, we have uncovered a number of rosiglitazone modulated genes and pathways that may play a role in the pathophysiology of the increase in cardiac mortality as seen in several recent meta-analyses. Specifically, the cumulative upregulation of (1) a matrix metalloproteinase gene that has previously been implicated in plaque rupture, (2) potassium channel genes involved in membrane potential maintenance and action potential generation, and (3) sphingolipid and ceramide metabolism-related genes, together give cause for concern over rosiglitazone's safety. Lastly, in vivo imaging studies revealed minimal differences between rosiglitazone-treated and untreated db/db mouse hearts, indicating that rosiglitazone's effects on gene expression in the heart do not immediately turn into detectable gross functional changes. CONCLUSIONS: This study maps the genomic expression patterns in the hearts of the db/db murine model of diabetes and illustrates the impact of rosiglitazone on these patterns. The db/db gene expression signature was markedly different from control, and was not reversed with rosiglitazone. A smaller number of unique and interesting changes in gene expression were noted with rosiglitazone treatment. Further study of these genes and molecular pathways will provide important insights into the cardiac decompensation associated with both diabetes and rosiglitazone treatment

RECENT DEVELOPMENTS IN THE APPLICATION OF THE MULTICHANNEL FABRY-PEROT TO PLASMA SPECTROSCOPY

L'interféromètre de Fabry-Pérot multi-canal par réflexion, s'est montré un instrument important pour l'analyse de la forme des raies spectrales quand une grande luminosité et une bonne résolution dans le temps sont nécessaires. Il a été appliqué à l'étude de plusieurs problèmes de physique des plasmas, par exemple la détermination de la température cinétique, dans une décharge "pinch" toroïdale dans un mélange d'hydrogène et d'hélium. Une nouvelle méthode utilisant des lentilles de Fresnel a été étudiée. Les mesures préliminaires indiquent que le nombre de canaux disponibles par cette méthode n'est limité que par la finesse de l'interféromètre.The reflection multichannel Fabry-Perot has proven an important tool for the analysis of spectral line shapes where high luminosity and good time-resolution are required. It has been applied to several plasma physics problems, for example to determine kinetic temperatures in a toroidal pinch discharge in a mixture of hydrogen and helium. A new method utilizing Fresnel lenses has been devised. Preliminary measurements indicate that the number of channels available by this method is limited only by the finesse of the interferometer

Emploi de fentes courbes pour la mise en série d'un réseau de diffraction avec un interféromètre fabry-Perot balayé par variation de pression

In the case of certain high resolution measurements, absorption for instance, the usual method, developed by P. Jacquinot and others, of employing the central region of the Fabry-Perot pattern may result in a loss of light due to geometry. For instance, with an f/10 grating with a 1 cm high exit slit, a 50 mm diameter Fabry-Perot, and a desired resolution of 5 x 105 in absorption, the light loss due to geometry is of the order of 4/5. It is shown that the situation can be much improved in certain cases by employing curved slits to match the curvature of the Fabry-Perot interference rings.Dans le cas de certaines mesures à haute résolution, en absorption par exemple, la méthode habituelle développée par P. Jacquinot et autres qui utilise la partie centrale de la figure de Fabry-Perot peut occasionner une perte de lumière en raison de la géométrie du système. Par exemple avec un réseau f/10 à fente de sortie de 1 cm de haut, un Fabry-Perot de 50 mm de diamètre et une résolution désirée de 5.105, en absorption, la perte de lumière due à des raisons géométriques est de l'ordre de 4/5. On montre que la situation peut, dans certains cas, être beaucoup améliorée par l'emploi de fentes courbes pour s'adapter à la courbure des anneaux d'interférence de Fabry-Perot

An International Comparison of Concentration and Diversity in the Food Processing Industry

International comparisons of market structure are complicated by a lack of comparable data. Although the U.S. Department of Commerce reports measures of industry concentration, they do not verify either the control of subsidiary firms or the possible multinational nature of their ownership nor are consistently based on sales. Other counties produce similar reports, but these studies are generally not comparable to U.S. values due, in part, to incompatible sector definitions. In addition, few government- sponsored studies provide firm-level detail or timely information. Furthermore, given the widespread multinational nature of many larger firms, an international analysis of ownership is necessary. This paper addresses the issues encountered in the construction of international market data from traditional financial report data and provides a set of methods for the comparison of measures of market concentration and industry diversity across countries. Using 1991 financial data, a firm level data set is constructed and used to compute comparable measures of market concentration and industry diversity for the U.S. and E.C. food processing industries