Testing for Unit Roots and the Impact of Quadratic Trends,with an Application to Relative Primary Commodity Prices

In practice a degree of uncertainty will always exist concerning what specification to adopt for the deterministic trend function when running unit root tests. While most macroeconomic time series appear to display an underlying trend, it is often far from clear whether this component is best modeled as a simple linear trend (so that long-run growth rates are constant) or by a more complicated nonlinear trend function which may, for instance, allow the deterministic trend component to evolve gradually over time. In this article, we consider the effects on unit root testing of allowing for a local quadratic trend, a simple yet very flexible example of the latter. Where a local quadratic trend is present but not modeled, we show that the quasi-differenced detrended Dickey–Fuller-type test of Elliott et al. (1996 Elliott , G. , Rothenberg , T. J. , Stock , J. H. ( 1996 ). Efficient tests for an autoregressive unit root . Econometrica 64 : 813 – 836 .[Crossref], [Web of Science ®] , [Google Scholar]) has both size and power which tend to zero asymptotically. An extension of the Elliott et al. (1996 Elliott , G. , Rothenberg , T. J. , Stock , J. H. ( 1996 ). Efficient tests for an autoregressive unit root . Econometrica 64 : 813 – 836 .[Crossref], [Web of Science ®] , [Google Scholar]) approach to allow for a quadratic trend resolves this problem but is shown to result in large power losses relative to the standard detrended test when no quadratic trend is present. We consequently propose a simple and practical approach to dealing with this form of uncertainty based on a union of rejections-based decision rule whereby the unit root is rejected whenever either of the detrended or quadratic detrended unit root tests rejects. A modification of this basic strategy is also suggested which further improves on the properties of the procedure. An application to relative primary commodity price data highlights the empirical relevance of the methods outlined in this article. A by-product of our analysis is the development of a test for the presence of a quadratic trend which is robust to whether the data admit a unit root.     

CRIME AND POLICE RESOURCES: THE STREET CRIME INITIATIVE

In this paper we look at the connection between police resources and crime by focussing on a large‐scale policy intervention—the Street Crime Initiative—that was introduced in England and Wales in 2002. This allocated additional resources to some police force areas to specifically target street crime, whereas other forces did not receive any additional funding. Estimates derived from several empirical strategies show that robberies fell significantly in SCI police forces relative to non‐SCI forces after the initiative was introduced. Moreover, the policy seems to have been a cost effective one, even after extensively testing for possible displacement or diffusion effects onto other crimes and into adjacent areas. Overall, we reach the conclusion that increased police resources can be used to generate falls in crime, at least in the context of the SCI program we study. (JEL: H00, H5, K42)     

Understanding and informing policy implementation: a case study of the domestic violence provisions of the Maryland Gun Violence Act

The Maryland Gun Violence Act, enacted into law in 1996, explicitly authorized courts to order batterers to surrender their firearms through civil protective orders. It also vested law enforcement with the explicit authority to remove guns when responding to a domestic violence complaint. In order to assess how these laws were implemented, we designed a case study and collected data from in-depth, key informant interviews, court observations, and relevant documents. We present findings from this study and recommend how to increase the likelihood that policies designed to separate batterers and guns are implemented in a way that will result in greater protections for victims of domestic violence.     

The use of the coefficient of variation in detecting sincerity of effort: a meta-analysis

The coefficient of variation (CV) is used to determine sincerity of effort of strength measurements. However, there is a controversy in the literature concerning its validity and effectiveness. We used a meta-analytic approach and calculated the effect size between maximal and submaximal efforts for the CV of grip, elbow flexion and knee extension. We summarized findings concerning stability, sensitivity and specificity of the CV. We found large effect sizes (d > or = 0.8) for all comparisons indicating that submaximal efforts were more variable than maximal efforts. We also found large error rates and low stability of the CV. The error rates and stability values of the CV are unacceptable from both a clinical and a medico-legal standpoint. Therefore, the use of the CV for assessing sincerity of effort needs to be questioned.     

Assessing the risk factors for suicidal thoughts at a nontraditional commuter school

The sample of students completing the National College Health Assessment (NCHA) Survey at the University of Utah differs from the national reference group for the NCHA 2003 in age, employment, residence, and marital status. The purpose of this study is to determine if the defining characteristics of a commuter school increase the risk for suicidal thoughts. During the fall semester of 2004, the University of Utah implemented a randomized electronic survey assessing the student body's health status in several areas. The authors compared 88 respondents who endorsed seriously considered suicide in the previous 12 months were with the remaining 954 respondents to identify discriminating variables. Those students who seriously considered suicide more likely lived off campus, indicated they were emotionally abused, were in only fair health, experienced being assaulted, experienced unwanted sexual touching, or were not heterosexual. Students who were employed were significantly less likely to consider suicide.     

Becoming Flexible: Self-flexibility and its Pedagogies

Much of the debate on flexibility has remained at a stubbornly macro, demographic level without looking closely at individual attempts to become more flexible. This paper argues that the debate on flexibility has been dominated by attention to the structural side, looking at flexi-time and part-time contracting, for example, to the neglect of what we call self-flexibility through self-reflexivity and self-transformation. The paper begins to redress this imbalance drawing upon two different cases which examine specific forms of self-flexibility: feedback and personal malleability and risk-taking through experiential learning. Drawing upon sociological research, we seek to examine critically the ways in which self-flexibilities are taken up and pursued by employees in their attempts to remain employable and their gendered implications.