Testing equality of variances in the analysis of repeated measurements

The problem of comparing the precisions of two instruments using repeated measurements can be cast as an extension of the Pitman-Morgan problem of testing equality of variances of a bivariate normal distribution. Hawkins (1981) decomposes the hypothesis of equal variances in this model into two subhypotheses for which simple tests exist. For the overall hypothesis he proposes to combine the tests of the subhypotheses using Fisher's method and empirically compares the component tests and their combination with the likelihood ratio test. In this paper an attempt is made to resolve some discrepancies and puzzling conclusions in Hawkins's study and to propose simple modifications.
The new tests are compared to the tests discussed by Hawkins and to each other both in terms of the finite sample power (estimated by Monte Carlo simulation) and theoretically in terms of asymptotic relative efficiencies.     

MSE-improvement of the least squares estimator by dropping variables

It is well known that dropping variables in regression analysis decreases the variance of the least squares (LS) estimator of the remaining parameters. However, after elimination estimates of these parameters are biased, if the full model is correct. In his recent paper, Boscher (1991) showed that the LS-estimator in the special case of a mean shift model (cf. Cook and Weisberg, 1982) which assumes no “outliers” can be considered in the framework of a linear regression model where some variables are deleted. He derived conditions under which this estimator outperforms the LS-estimator of the full model in terms of the mean squared error (MSE)-matrix criterion. We demonstrate that this approach can be extended to the general set-up of dropping variables. Necessary and sufficient conditions for the MSE-matrix superiority of the LS-estimator in the reduced model over that in the full model are derived. We also provide a uniformly most powerful F-statistic for testing the MSE-improvement.     

On the human aspects in structural modeling

This article deals with two facets of structural modeling often ignored: a) the several human roles that effective participative modeling must encompass, and b) the group procedures developed to assist modelers in defining the elements of the system to be modeled. The roles are 1) the method technician, 2) the facilitator, and 3) the participant. Their recognition on the part of the technology assessment leader is vital to the successful conduct of participative modeling. The element-generating group procedures surveyed here are organized into two categories: those which emphasize an atmosphere for free-wheeling thinking, and those which emphasize structured guidance (either through use of words or geometric and analytic techniques).     

On the theory of macroeconomic quasi-equilibria

Conclusion It has been shown that for the Classical System a quasi-equilibrium cannot exist, unless we make the ad hoc assumption of inflexible nominal wages⁸. The equilibrium in the classical regime corresponds to the general competitive equilibrium, and of course the validity of Walras' Law cannot be questioned. At the same time, however, it has been shown that to extend these conclusions to the Keynesian system as well is not justified. The Keynesian system has, in general, a quasi-equilibrium. The model constructed in this paper and the resulting conclusions are significant because the model: (a) Incorporates the Keynesian notion of effective demand, which includes the demand for capital goods (investment) as being performed by a group of people distinct from the consumers (and so, answering Negishi's point, there is a prince in Hamlet!), (b) Unlike other models (like the recent paper by Glustoff), it does not rely on nominal wage rigidity to explain unemployment, but instead, again answering Negishi's remark, it explains rather than postulates why real wages do not adjust in the presence of unemployment so as to eliminate it. (c) It verifies the validity of Clower's proposition that in the Keynesian System Walras' Law holds only in equilibrium. (d) It reconsiles Bent Hansen's original quasi-equilibrium model with the Keynesian proposition of an unemployment equilibrium, against the apparent view of Hansen that to do that would require the assumption of a Phillips curve, a view also shared by Arrow and Hahn, and many others.An earlier version of this paper was presented in the December 1974 meeting of the Econometric Society in San Francisco. The author wishes to thank Prof. R. Clower, Prof. B. Hansen, Prof. S. Black, and Dr. G. Winckler for their valuable comments, but he obviously claims any errors for himself.     

美国房地产泡沫的崩盘:全球经济的魔鬼?

美国的房地产投机泡沫正在破裂。这种转变将通过多种途径影响到美国经济:建筑业下滑将使美国经济增长率减少约1．5个百分点,而财富效应的逆转会造成约0．5个百分点的影响。加之其他因素．房地产泡沫破裂将使美国经济增长率降低2．0个百分点以上。而对于失衡的全球经济而言．美国房地产泡沫的破裂将会造成很大影响。     

Putting supplies at the bedside via the Friesen concept

Hospitals designed using the concepts of architect Gordon Friesen are especially conducive to reengineering for patient-focused care. The Nurserver, a closet-like space outside each patient's room, makes it very easy for hospitals to redesign their methods for delivering supplies so that caregivers seldom have to go more than a few feet to get what they need. In this article, staff of Monongalia General Hospital in Morgantown, West Virginia, describe how they have used the Friesen design to modify supply distribution processes.     

Problem-solving in teaching/learning packages for Technology

In the project Technology in Secondary Education: Problem-solving in Teaching/learning Packages, two experiments regarding a construction problem and an explanation problem were conducted, in which two variants of a teching/learning package (strongly structuredvs. weakly structured) were compared. Only with the strongly structured instructional variant of the package for the explanation problem did the pupils come to a quick solution of the problem. In both experiments, the factors that influenced the problem-solving processes of the pupils were investigated. The results are of importance for curriculum developers and the authors of teaching/learning packages for Technology but further research into the factors influencing the problem solving process of pupils is necessary.