Fractional principal components regression: a general approach to biased estimators

Several biased estimators have been proposed as alternatives to the least squares estimator when multicollinearity is present in the multiple linear regression model. The ridge estimator and the principal components estimator are two techniques that have been proposed for such problems. In this paper the class of fractional principal component estimators is developed for the multiple linear regression model. This class contains many of the biased estimators commonly used to combat multicollinearity. In the fractional principal components framework, two new estimation techniques are introduced. The theoretical performances of the new estimators are evaluated and their small sample properties are compared via simulation with the ridge, generalized ridge and principal components estimators     

Asymptotic Confidence Limits for Performance Measures of a Repairable System with Imperfect Service Station

This article studies the asymptotic confidence limits for the steady-state availability, failure frequency, and mean time to failure of a repairable K-out-of-(M + S) system with M operating devices, S spares, and an imperfect service station that may be interrupted by a breakdown when it is repairing for the failed devices.     

ECONOMIC GROWTH REGRESSIONS FOR THE AMERICAN STATES: A SENSITIVITY ANALYSIS

We use extreme-bounds analysis to assess the sensitivity of numerous control variables identified in the state growth literature. We employ annual panel data on the American states to identify which variables are robust to small changes in the conditioning information set. The results provide a set of core variables as a starting point for future research that relies on state growth regressions. The findings also demonstrate that several important conclusions in the literature depend on how variables are measured. ( JEL R11, O23, C23, 018)     

Interrelated family-building behaviors: Cohabitation, marriage, and nonmarital conception

Data from the National Longitudinal Study of the High School Class of 1972 are used to estimate a series of models of entry into marriage, entry into cohabitation, and nonmarital pregnancy. Our models account explicitly for the endogeneity of one outcome as a predictor of another by taking into account both heterogeneity across individuals due to unmeasured factors that may affect all these outcomes and the correlation in the unmeasured factors across processes. We find that these heterogeneity components are strongly and positively related across the outcomes. Women who are more likely to cohabit, marry, or become pregnant while unmarried are also more likely to do each of the others. Although black and white women differ in the likelihood of these behaviors, the interrelations of the behaviors are quite similar across groups.     

Malthusian models and Chinese realities: the Chinese demographic system, 1700-2000

This article summarizes major recent findings on Chinese demographic behavior and outlines their relevancy for the Malthusian model of comparative population dynamics and Chinese population in particular. Specifically, it considers four distinctive and persistent features of Chinese behavior during the last 300 years—high rates of female infanticide and abortion, high rates of bachelorhood, low marital fertility, and high rates of male and female adoption–and discusses the origins and implications of such a demographic regime for Chinese economic and social development. Contrasting Chinese demographic behavior with European demographic behavior, the article argues the existence of a demographic system and a demographic transition different from current Malthusian and neo-Malthusian models, and the existence of a system regulating collective demographic behavior in ways distinctly different from Western experience.     

An E-mail assessment of undergraduates' attitudes toward smoking.

Responses from 513 of 1,000 randomly selected undergraduate students who were sent an e-mail questionnaire, about cigarette smoking were analyzed. Thirteen percent of the respondents identified themselves as smokers. No statistically significant differences were observed between smokers and nonsmokers and year in college, sex, age, race, or having attended public or private high schools. Ninety-eight percent of the respondents considered themselves knowledgeable about adverse health consequences of smoking, yet 39.1% of current smokers seriously considered stopping smoking, and 11.5% of current nonsmokers intended to start smoking. The preferred quitting method of smokers and ex-smokers was stopping all at once ("cold turkey"). Fifty-two percent of the smokers did not want professional assistance to stop smoking; 40% of the nonsmokers wanted information on second-hand smoke.     

OR models as tools for the regulation of industry

This paper presents some novel observations and recommendations about the uses and usefulness of operational research models as a tool for regulation of industry. Reference is made to the first use of a model for regulatory analyses by the United States Federal Power Commission in a natural gas proceeding. A criticism is given of this first attempt to use a model for regulatory purposes, and from this criticism a strategy for a more effective use of models is developed. As a part of this strategy the concept of ex post models is introduced. In addition the potential conflict of model use and the guarantee of due process of law is considered. The paper concludes with a set of remarks on the recommended posture that an operational research analyst should assume when working with policy makers.     

Sensitivity of Physiologically Based Pharmacokinetic Models to Variation in Model Parameters: Methylene Chloride

The parameters in a physiologically based pharmacokinetic (PBPK) model of methylene chloride were varied systematically, and the resulting variation in a number of model outputs was determined as a function of time for mice and humans at several exposure concentrations. The importance of the various parameters in the model was highly dependent on the conditions (concentration, species) for which the simulation was performed and the model output (dose surrogate) being considered. Model structure also had a significant impact on the results. For sensitivity analysis, particular attention must be paid to conservation equations to ensure that the variational calculations do not alter mass balance, introducing extraneous effects into the model. All of the normalized sensitivity coefficients calculated in this study ranged between −1.12 and 1, and most were much less than 1 in absolute value, indicating that individual input errors are not greatly amplified in the outputs. In addition to ranking parameters in terms of their impact on model predictions, time-dependent sensitivity analysis can also be used as an aid in the design of experiments to estimate parameters by predicting the experimental conditions and sampling points which will maximize parameter identifiability.     

The principles of war applied to business

The search for excellence in business is not enough. First a company has to survive before it can become excellent. Competition in the marketplace is a form of warfare. Twenty centuries of military history have produced principles of warfare that business executives can adapt for use in today's competitive environment. The Chinese have a “Society for the Study of Ancient Management Thinking.” Japan's success after World War II, they explain “a little bitterly”, owes much to its study of ancient Chinese wisdom, particularly Sun Tzu'sThe Art of War, which the Japanese use as a treatise on market strategy. Businessmen must use all the tools available to them to survive and prosper.