Wavelet shrinkage for unequally spaced data

Wavelet shrinkage (WaveShrink) is a relatively new technique for nonparametric function estimation that has been shown to have asymptotic near-optimality properties over a wide class of functions. As originally formulated by Donoho and Johnstone, WaveShrink assumes equally spaced data. Because so many statistical applications (e.g., scatterplot smoothing) naturally involve unequally spaced data, we investigate in this paper how WaveShrink can be adapted to handle such data. Focusing on the Haar wavelet, we propose four approaches that extend the Haar wavelet transform to the unequally spaced case. Each approach is formulated in terms of continuous wavelet basis functions applied to a piecewise constant interpolation of the observed data, and each approach leads to wavelet coefficients that can be computed via a matrix transform of the original data. For each approach, we propose a practical way of adapting WaveShrink. We compare the four approaches in a Monte Carlo study and find them to be quite comparable in performance. The computationally simplest approach (isometric wavelets) has an appealing justification in terms of a weighted mean square error criterion and readily generalizes to wavelets of higher order than the Haar.     

Least Squares Model Averaging

This paper considers the problem of selection of weights for averaging across least squares estimates obtained from a set of models. Existing model average methods are based on exponential Akaike information criterion (AIC) and Bayesian information criterion (BIC) weights. In distinction, this paper proposes selecting the weights by minimizing a Mallows criterion, the latter an estimate of the average squared error from the model average fit. We show that our new Mallows model average (MMA) estimator is asymptotically optimal in the sense of achieving the lowest possible squared error in a class of discrete model average estimators. In a simulation experiment we show that the MMA estimator compares favorably with those based on AIC and BIC weights. The proof of the main result is an application of the work of Li (1987).     

Marketing’s contribution to business strategy: market orientation,relationship marketing and resource-advantage theory

Although overlooked to some degree by non-marketing disciplines, the discipline of marketing has contributed significantly to the body of knowledge on business strategy over the last two decades. This paper evaluates these contributions, examines how they complement dominant non-marketing theories of business strategy, and shows how marketing offers a generalized theory of competition that integrates the concepts of both marketing and non-marketing theories of business strategy.     

Piece rate pay

The theory of piece-rate pay suggests firms may be able to adjust their variable costs by altering work standards and the piece rate itself. Another argument holds that piece-rate systems can economize on the cost of monitoring worker output, that such systems are a substitute for management. Union positions on these points have supported the notion that piece-rate pay can be both a benefit and a cost to workers, depending on the cost of monitoring. However, competitive forces ultimately force all pay systems to reflect the opportunity costs of all factors of production.     

Mark-resighting analysis of a California gull population

California gulls ( Larus californicus ) of known age and sex were censused on their breeding colony in 1979, 1980 and 1984 through 1993. Ages of 235 males and 196 females ranged from 4 to 27 years. Age classes used in the analysis were limited to 17, 4 through 19, and 20 or more as a final age category because data on gulls over 20 were sparse. Survival declined with age in a way that was parsimoniously modelled with a quadratic function. Other factors, sex and time, did not explain any variation in survival. Resighting depended on age, sex and time. Younger adults skipped breeding more frequently than did older adults, and females skipped breeding more frequently than did males. There was also good evidence for time dependence in resighting probability, but its inclusion in the model occurred at the expense of interpretability and precision. In a data set such as this, resighting probability may assume more importance than a mere 'nuisance parameter'. In this study, resighting history measured attendance at the breeding ground. In turn, attendance rates may be a manifestation of reproductive strategy, which can also have consequences for survival. In this situation, there may be heterogeneity in both survival and resighting probability that is unexplained by the model. While such complexity may well be a nuisance to deal with, it can also point to important biological questions.     

COGNITIVE BRIDGES:

This article explores the problem of social integration from a position of isolation. It uses the experiences of high school undercover officers to consider the problem conceptually. Officers must move from new student to peer to drug purchaser without any informant assistance and with severe time constraints. Three specific techniques are used to trigger this process: class clowning, retreatism, and troublemaking. Each is a variation on the single theme of rebellion. I argue that these techniques generate interpersonal familiarity from a distance by creating reputations that drug dealers identify with and vest legitimacy in. Reputation substitutes for introductions informants could otherwise give, establishes a pretransaction comfort zone, and lays the interpersonal groundwork officers need before they can solicit drugs. Officers' behavior is conceptualized through the notion of a cognitive bridge, a hybrid of interactionist and microstructural principles. Data are drawn from interviews with thirty undercover officers who operate from a large western U.S. municipality.     

IT'S MY WORLD?

A positive sense of control over one's life is essential for maintaining health and well-being. Those with a strong sense of control believe changes in their social world are responsive to their choices, actions, and efforts. In contrast, a sense of powerlessness or fatalism is on the other end of the continuum. There is little research that explores how race and gender relate to feelings about personal control. To examine their effects on perceptions of personal control, we analyze data from the American Changing Lives Survey, 1986. Controlling for race and gender in the full model led to results that failed to reveal the complexity of relationships when compared with results of analyses among the subgroups. Some key factors distinct for the various groups were, for white men, functional health, positive support from friends and relatives, and having people to share their feelings with; for black men, age and visiting mental health facilities; for white women, visiting medical care facilities, the number of children, tobacco, and having someone to call for help; and, for black women, being involved with organizations (groups, clubs, and churches) and religion. When there are no significant racial or gender differences, examining models simultaneously stratified by race and gender introduced a more dynamic and multidimensional relationship between the control and dependent variables than was previously understood.