A Stochastic Volatility Model With Markov Switching

This article presents a new way of modeling time-varying volatility. We generalize the usual stochastic volatility models to encompass regime-switching properties. The unobserved state variables are governed by a first-order Markov process. Bayesian estimators are constructed by Gibbs sampling. High-, medium- and low-volatility states are identified for the Standard and Poor's 500 weekly return data. Persistence in volatility is explained by the persistence in the low- and the medium-volatility states. The high-volatility regime is able to capture the 1987 crash and overlap considerably with four U.S. economic recession periods.     

Developing Policy in the Face of Scientific Uncertainty: Interpreting 0.3 μT or 0.4 μT Cutpoints from EMF Epidemiologic Studies

There has been considerable scientific effort to understand the potential link between exposures to power-frequency electric and magnetic fields (EMF) and the occurrence of cancer and other diseases. The combination of widespread exposures, established biological effects from acute, high-level exposures, and the possibility of leukemia in children from low-level, chronic exposures has made it both necessary and difficult to develop consistent public health policies. In this article we review the basis of both numeric standards and precautionary-based approaches. While we believe that policies regarding EMF should indeed be precautionary, this does not require or imply adoption of numeric exposure standards. We argue that cutpoints from epidemiologic studies, which are arbitrarily chosen, should not be used as the basis for making exposure limits due to a number of uncertainties. Establishment of arbitrary numeric exposure limits undermines the value of both the science-based numeric EMF exposure standards for acute exposures and precautionary approaches. The World Health Organization's draft Precautionary Framework provides guidance for establishing appropriate public health policies for power-frequency EMF.     

International venture capital research: From cross-country comparisons to crossing borders

Venture capital (VC) has become an international phenomenon, and VC firms are a specific kind of service firm whose characteristics have distinctive implications for international behaviour. There is now a disparate body of research on international aspects of VC across a number of disciplines comprising finance, economics, strategy, entrepreneurship, international business and economic geography. A novel aspect of this paper is that we review and synthesize this disparate literature. A number of research gaps and limitations in the theoretical and methodological approaches involved in previous studies are identified and suggestions made for further research. We show that the vast majority of the literature relates to cross-country comparisons; that is, macro-level comparisons of VC industries across different countries and micro-level comparisons of VC behaviour across countries. From our review of the literature, we argue that an under-researched area concerns the influence of institutional contexts, especially the role of social networks and cultures. Furthermore, our review of the literature indicates that there is a major research gap in relation to work dealing with the crossing of country borders by VC firms. We suggest that resource-based, capabilities, institutional and network theories may be offer insights to further our understanding of the behaviour of VC firms in this area.     

Cultural transmission,educational attainment and social mobility

This paper examines the relationship between cultural socialisation, educational attainment and intergenerational social mobility. Picking up on debates about the transmission of cultural capital and social advantage, we use data from the Taking Part Survey of England to analyse how far socialisation into cultural activities and encouragement play a role in educational attainment, intergenerational mobility and in the reproduction of class. This survey has unprecedented data on whether respondents had been taken to museums/art galleries, theatre/dance/classical music performances, sites of historic interest, and libraries when they were growing up. This is buttressed by information on how much parents or other adults encouraged the respondents to read books or to be creatively active in different domains of the arts, literature and music. Using these rich measures of childhood socialisation, we can show that part of the effect of parental class on educational attainment is due to the transmission of this kind of cultural capital. Moreover, this transmission also has a direct effect on the level of educational attainment. In a similar fashion, respondents who have experienced a higher intensity of cultural socialisation are more likely to be upwardly mobile, and likewise, cultural transmission has a positive effect on the prevention of downward mobility among service class children. These results are discussed in the light of current issues in British mobility research and its treatment of cultural aspects of class and mobility.     

School Students at Work

Over half of three hundred fifth-formers surveyed had taken holiday jobs and over a third worked part-time during the school term. The average remuneration for those who worked was $1.75 for boys and $1.20 for girls and the average time in employment per week was almost twenty hours in the holidays and about seven and a half during term. While the respondents reported that they worked for money and to gain acceptance in the adult world, a majority of them stated that they favoured compulsory work experience, advocating that all students should spend time on farms or in factories as part of their education.     

Partisanship and Support for Propositions on the Ballot: A State-Level Longitudinal Study

Objective . Previous studies suggest that there is reason to believe that changes in the partisan composition of a state's electorate will be associated with changes in the level of support for certain types of propositions on the ballot. Scholars, however, differ over the reasons for this relationship. Some have suggested the importance of party differences over substantive issues. Others have indicated the importance of differences among partisans in their willingness to defer to legislative judgments or recommendations. Still others have pointed to the importance of partisan cue taking; for example, that Republicans are more likely to vote for propositions put on the ballot by Republican legislatures and Democrats are likely to oppose such measures. We test these rival hypotheses. Methods . Using multivariate analysis and time series techniques, we examine voting patterns on 361 propositions submitted to voters in Arizona from 1912 to 1996. Results . We find that increases in the Republican vote were significantly linked to increase in support for measures submitted by state legislatures, particularly legislatures controlled by Republicans. Conclusions . The findings give some support to deference theory and to the notion that a subtle process of partisan cue taking may be involved in proposition voting.     

Estimating numbers of infectious units from serial dilution assays

Summary.  The paper concerns the design and analysis of serial dilution assays to estimate the infectivity of a sample of tissue when it is assumed that the sample contains a finite number of indivisible infectious units such that a subsample will be infectious if it contains one or more of these units. The aim of the study is to estimate the number of infectious units in the original sample. The standard approach to the analysis of data from such a study is based on the assumption of independence of aliquots both at the same dilution level and at different dilution levels, so that the numbers of infectious units in the aliquots follow independent Poisson distributions. An alternative approach is based on calculation of the expected value of the total number of samples tested that are not infectious. We derive the likelihood for the data on the basis of the discrete number of infectious units, enabling calculation of the maximum likelihood estimate and likelihood-based confidence intervals. We use the exact probabilities that are obtained to compare the maximum likelihood estimate with those given by the other methods in terms of bias and standard error and to compare the coverage of the confidence intervals. We show that the methods have very similar properties and conclude that for practical use the method that is based on the Poisson assumption is to be recommended, since it can be implemented by using standard statistical software. Finally we consider the design of serial dilution assays, concluding that it is important that neither the dilution factor nor the number of samples that remain untested should be too large.