Direct and Indirect Causal Effects via Potential Outcomes*

Abstract. The use of the concept of ‘direct’ versus ‘indirect’ causal effects is common, not only in statistics but also in many areas of social and economic sciences. The related terms of ‘biomarkers’ and ‘surrogates’ are common in pharmacological and biomedical sciences. Sometimes this concept is represented by graphical displays of various kinds. The view here is that there is a great deal of imprecise discussion surrounding this topic and, moreover, that the most straightforward way to clarify the situation is by using potential outcomes to define causal effects. In particular, I suggest that the use of principal stratification is key to understanding the meaning of direct and indirect causal effects. A current study of anthrax vaccine will be used to illustrate ideas.     

Banks winners in tournaments are difficult to recognize

Given a tournament T, a Banks winner of T is the top vertex of any maximal (with respect to inclusion) transitive subtournament of T. In this technical note, we show that the problem of deciding whether some fixed vertex v is a Banks winner for T is NP-complete. Received: 22 February 2002/Accepted: 20 June 2002 Supported by the START program Y43-MAT of the Austrian Ministry of Science. I would like to thank two thank the referees for a careful reading of the paper, for helpful remarks, and for many suggestions how to improve the presentation.     

Unresolved Conflicts in the Regional Security System: The Case of the South Caucasus

The collapse of the USSR was accompanied by transformation of the South Caucasian latent ethnopolitical conflicts into local wars. Today the situation in the area of the conflicts is “neither war, nor peace”. Three unresolved conflicts of the South Caucasus can be considered as one of the most serious obstacles for establishing a regional security system.The article gives the general characteristics of these conflicts, the trends of their development, taking into account the time factor, and analyzes the behavioral models of the main players – de jure recognized and unrecognized de facto states of the South Caucasus. The basic objective of the main players should be to keep the situation on a level preventing the resumption of the armed conflicts. The attempts of forced resolution of the conflicts are fraught with destabilization of the situation not only in the area of any of these conflicts but in the whole region.     

A simple procedure for the selection of significant effects

Summary.  Given a large number of test statistics, a small proportion of which represent departures from the relevant null hypothesis, a simple rule is given for choosing those statistics that are indicative of departure. It is based on fitting by moments a mixture model to the set of test statistics and then deriving an estimated likelihood ratio. Simulation suggests that the procedure has good properties when the departure from an overall null hypothesis is not too small.     

Trade-Offs Between Formal Home Health Care and Informal Family CareGiving

Using 1994 National Long Term Care Survey data, we estimated logistic regressions of formal and informal home health care use and hours. Home health care use and intensity were differentially impacted by chronic conditions, are higher for Medicaid enrollees and rural or small town residents, but lower for HMO enrollees. Decreases in the probability of home health care use increased informal instrumental activities of daily living (IADL) support four hours and decreased informal activities of daily living (ADL) support eight hours weekly. IADL caregiving substituted for formal care, but ADL caregiving declined with reductions in formal care. Public policy reducing formal home health care access may reduce informal ADL caregiving and increase informal IADL caregiving, producing net declines in support.     

Generalized quasi-likelihood

The quasi-score function, as defined by Wedderburn (1974) and McCullagh (1983) and so on, is a linear function of observations. The generalized quasi-score function introduced in this paper is a linear function of some unbiased basis functions, where the unbiased basis functions may be some linear functions of the observations or not, and can be easily constructed by the meaning of the parameters such as mean and median and so on. The generalized quasi-likelihood estimate obtained by such a generalized quasi-score function is consistent and has an asymptotically normal distribution. As a result, the optimum generalized quasi-score is obtained and a method to construct the optimum unbiased basis function is introduced. In order to construct the potential function, a conservative generalized estimating function is defined. By conservative, a potential function for the projected score has many properties of a log-likelihood function. Finally, some examples are given to illustrate the theoretical results. This paper is supported by NNSF project (10371059) of China and Youth Teacher Foundation of Nankai University.     

Ideas versus ideology: The origins of modern labor economics

Starting with its early twentieth century origins, the development of Labor Economics is traced to the present. We describe an intellectual revolution in which an earlier tra-dition that focused primarily on the institution of the labor union has been replaced by a perspective that emphasizes the various roles played by labor markets in an eco-nomic system. That earlier tradition contained very significant ideological elements, whereas its successor deals much more with the world of ideas. In the course of the debate, which still continues, ideas triumphed over ideology and created modern Labor Economics.