Some specifics on the brain drain from the Andean region

An analysis of the brain drain from the Andean countries of Bolivia, Chile, Colombia, Ecuador, and Peru to the United States is presented. The data are from a survey of 62 persons from those countries who are currently residing in the United States and are listed in the current edition of "American Men and Women of Science". The reasons why they left their country of origin and are staying in the United States are considered. (summary in FRE, SPA)     

Errata

My article entitled "Replications, Significance Tests, and Confidencein Findings in Survey Research" (POQ 47:261–69) is marredby a serious error which has implications for most of the contentsof the article. Table 1, which is adapted from a table published by Rosenthaland Hall,¹ gives the critical values of required for significance at several levels; itdoes not give the critical values of Trans , or () (). Rather, the latter should be referreddirectly to a table giving the areas under the normal curve,or, in other words, it should be treated as though it were aZ from a single-sample test. This means that the comparisons of significance test resultsfrom pooled data and from series of replications in Tables 2and 3 do not support the conclusion that using a replicate designrather than pooled data lessens the probability of Type II errors.In the case of Table 2, the probability from the pooled sampleis lower than the correct one from the series of replications,and in the case of Table 3, the probabilities are about thesame. The data in Table 4 illustrate a kind of situation in whicha replicate design may be the preferred one for another reason.The replicate design allows an estimate of sampling variabilityfrom the actual variability among a small number of samples,whereas the single-sample and pooled-sample significance testresults may be substantially in error due to the unstable meaningof the "zero" assigned to the reference category for the dummyvariables. However, the estimated probability for the arrayof replications should be .05 rather than the probability reported. Another error with less serious implications for the paper asa whole is that the third "alternative formula" for Trans is incorrect as printed. One of thefirst two formulas, or () (), should be used instead. The major error resulted from a misreading of the paper by Rosenthaland Hall. I apologize to Rosenthal and Hall and to any readersof my paper who have used the table of critical values incorrectlyin their research.     

AN ANALYSIS OF THE DYNAMIC THEORY OF THE MULTI—PRODUCT FIRM USING THE CALCULUS OF VARIATIONS

The purpose of this paper is to present the theory of the multi-product firm in situations where the revenue function depends not only on the rate of output but also on changes in the rate of output, and, similarly, where the cost function depends on changes in the rate of factor utilization as well as the rate of their utilization. Since the analysis will utilize the calculus of variations, a general introduction to this technique is also presented. The model analyzed assumes perfect foresight and knowledge concerning the revenue, cost, and production functions, and the calculus of variations is used to derive the conditions for an extremum. The first section presents the mathematical model and the model of the firm, and the optimality conditions are discussed in the second section.     

Theory Trimming

This paper attempts to show that the “Theory Trimming” technique makes little contribution to theory in sociology. A brief history of the technique is given, and several key assertions of its proponents are abstracted. These assertions are shown to be highly questionable. The general alternative to Theory Trimming is shown, and the relationship between Theory Trimming and more general orientations to research is discussed.     

SENSITIVITY ANALYSIS WITH INTERACTION EFFECTS

The purpose of this paper is to extend the sensitivity analysis methodology as it applies to linear programming. The methodology developed herein is concerned with those changes in a technological coefficient that cause simultaneous changes in the relevant cost coefficients of the objective function. By proceeding from the definitions of feasibility and optimality, the authors develop formulas for determining bounds on the extent to which a technological coefficient, which has a predetermined effect on the corresponding cost coefficient, can vary without changing the optimal set of activities. After the formulas are developed, their use is demonstrated on a product-mix problem. This technique is of interest because changes in the rate at which an input is utilized can be expected to change the cost per unit of a resulting product. This interdependence should be recognized whenever a sensitivity analysis is performed on a technological coefficient of either a cost minimization or a contribution margin maximization problem.     

MATERIAL REQUIREMENTS PLANNING UNDER UNCERTAINTY

This paper presents a framework for characterizing and studying the uncertainty which can affect inventory investment and service level performance in a material requirements planning (MRP) system. It also presents the results of a simulation experiment which compared two techniques (safety stock and safety lead time) for building inventory to protect against uncertainty. The simulation results disclose consistent differences between the techniques in protecting a representative part against timing and quantity uncertainty in both demand and supply for the part. The paper not only provides some initial insights into the behavior of MRP systems under uncertainty, but also establishes some guidelines for choosing between safety stock and safety lead time.     

Bayesian analysis of human movement curves

Summary.  We consider the Bayesian analysis of human movement data, where the subjects perform various reaching tasks. A set of markers is placed on each subject and a system of cameras records the three-dimensional Cartesian co-ordinates of the markers during the reaching movement. It is of interest to describe the mean and variability of the curves that are traced by the markers during one reaching movement, and to identify any differences due to covariates. We propose a methodology based on a hierarchical Bayesian model for the curves. An important part of the method is to obtain identifiable features of the movement so that different curves can be compared after temporal warping. We consider four landmarks and a set of equally spaced pseudolandmarks are located in between. We demonstrate that the algorithm works well in locating the landmarks, and shape analysis techniques are used to describe the posterior distribution of the mean curve. A feature of this type of data is that some parts of the movement data may be missing—the Bayesian methodology is easily adapted to cope with this situation.