The Optimal Degree of Discretion in Monetary Policy

How much discretion should the monetary authority have in setting its policy? This question is analyzed in an economy with an agreed‐upon social welfare function that depends on the economy's randomly fluctuating state. The monetary authority has private information about that state. Well designed rules trade off society's desire to give the monetary authority discretion to react to its private information against society's need to prevent that authority from giving in to the temptation to stimulate the economy with unexpected inflation, the time inconsistency problem. Although this dynamic mechanism design problem seems complex, its solution is simple: legislate an inflation cap. The optimal degree of monetary policy discretion turns out to shrink as the severity of the time inconsistency problem increases relative to the importance of private information. In an economy with a severe time inconsistency problem and unimportant private information, the optimal degree of discretion is none.     

A Qualitative Assessment of South African Adolescents' Motivations For and Against Substance Use and Sexual Behavior

Focus groups (N=15 groups; 8 with girls, 7 with boys) with adolescents in high schools near Cape Town, South Africa, were used to conduct a qualitative investigation of reported reasons for using and not using substances and for having and not having sex. Adolescents reported Enhancement, Negative States, Social, and Aversive Social motivations for both substance use and sexual behavior. In addition, being addicted as a reason for using drugs and rape as a context for sexual behavior were frequently reported. Motivations against behaviors included Physical/Behavioral Consequences, Ethical Objections, Social Disapproval, and Incompatible Activities and Goals reasons. Preventive interventions should address existing motivations for and against substance use and sexual behavior to acknowledge adolescents' experiences in context.     

Testing for co-directional interactions using union–intersection and intersection–union methods

When interaction terms exist in a two-factor, factorial experiment, the consideration and analysis of main effects are often restricted to those situations where the interaction between factors is not significant. Hinkelman and Kempthorne [4 Hinkelmann, K. and Kempthorne, O. 1994. Design and Analysis of Experiments. Volume 1: Introduction to Experimental Design, New York: Wiley.  [Google Scholar]] softened that stance somewhat and advocate testing main effects when the interaction is deemed co-directional but not anti-directional. A test for the main effects in that situation may be pragmatic to the practitioner and appealing to researchers in other disciplines. Intersection–union and union–intersection methods are examined for assessing the directional nature of significant interactions so that the main effects in a two-factor factorial may be evaluated. The tests suggested are conceptually straightforward and practical and maintain the nominal Type-I error rate. Examples are provided to illustrate the methods.     

COORDINATE DESCENT ALGORITHMS FOR NONCONVEX PENALIZED REGRESSION, WITH APPLICATIONS TO BIOLOGICAL FEATURE SELECTION

A number of variable selection methods have been proposed involving nonconvex penalty functions. These methods, which include the smoothly clipped absolute deviation (SCAD) penalty and the minimax concave penalty (MCP), have been demonstrated to have attractive theoretical properties, but model fitting is not a straightforward task, and the resulting solutions may be unstable. Here, we demonstrate the potential of coordinate descent algorithms for fitting these models, establishing theoretical convergence properties and demonstrating that they are significantly faster than competing approaches. In addition, we demonstrate the utility of convexity diagnostics to determine regions of the parameter space in which the objective function is locally convex, even though the penalty is not. Our simulation study and data examples indicate that nonconvex penalties like MCP and SCAD are worthwhile alternatives to the lasso in many applications. In particular, our numerical results suggest that MCP is the preferred approach among the three methods.     

Significant harm: making professional judgements

Judging whether a child is suffering or is likely to suffer significant harm has become a critical task for professionals working with children and their families in England and Wales. Yet little guidance is available about what the phrase means in its entirety and how it should be applied in practice. This study set out to examine how the phrase was used in practice by a selected sample of experienced health and social work staff. The evidence collected suggests flaws in the general approach adopted by professionals to identification and assessment in child protection cases. The data indicate a heavy concentration of attention on the weaknesses of families being assessed rather than their strengths and on parents rather than children. Problems are identified in responding effectively to long-term, chronic abuse such as emotional abuse and neglect. The study recommends changes in practice based on these findings which have been implemented by a wide range of practice agencies within the study area. © 1998 John Wiley & Sons, Ltd.     

Commodity Price Volatility,Vulnerability and Development

This article examines the meaning and consequences of the developing countries’ vulnerability to the volatility of commodity prices. It first considers how to define and measure a country’s shocks and exposure arising from commodity price volatility in order to identify structural as distinct from policy vulnerability. The main channels through which price vulnerability influences economic growth are then presented. Finally, the policy implications for development aid, its allocation and design, are outlined. It is found that, while structural vulnerability is bad for growth, a policy of openness contributes to resilience. With the right rules, aid could play an important growth‐enhancing and poverty‐reducing role if allocated at least partly on the basis of vulnerability.     

International Business Cycles with Endogenous Incomplete Markets

Backus, Kehoe, and Kydland (1992), Baxter and Crucini (1995), and Stockman and Tesar (1995) find two major discrepancies between standard international business cycle models with complete markets and the data: In the models, cross‐country correlations are much higher for consumption than for output, while in the data the opposite is true; and cross‐country correlations of employment and investment are negative, while in the data they are positive. This paper introduces a friction into a standard model that helps resolve these anomalies. The friction is that international loans are imperfectly enforceable; any country can renege on its debts and suffer the consequences for future borrowing. To solve for equilibrium in this economy with endogenous incomplete markets, the methods of Marcet and Marimon (1999) are extended. Incorporating the friction helps resolve the anomalies more than does exogenously restricting the assets that can be traded.     

电影制作和发行过程中的安全漏洞分析

电影产业主要关心的一个问题是非法的（即未经授权的）电影复制行为。尽管非法的电影拷贝已经借助便携式物理媒介而得到传播,但低成本的高速宽带连接和P2P文件共享网络则能提供极其高效的传播媒介。本文对电影的制作和发行过程进行了简要分析,并指出了一些潜在的安全漏洞,这些漏洞使得非法电影拷贝能够被那些试图再次传播之的人所获取。