Leverage,influence and residuals in regression models when observations are correlated

This paper considers the concepts of leverage and influence in the linear regression model with correlated errors when the error covariance structure is completely specified. Generalizations of the usual measures are given. Extensions of residuals also naturally arise. The theory is illustrated using two examples     

Direct and Indirect Effects Based on Difference-in-Differences With an Application to Political Preferences Following the Vietnam Draft Lottery

Abstract

We propose a difference-in-differences approach for disentangling a total treatment effect within specific subpopulations into a direct effect and an indirect effect operating through a binary mediating variable. Random treatment assignment along with specific common trend and effect homogeneity assumptions identify the direct effects on the always and never takers, whose mediator is not affected by the treatment, as well as the direct and indirect effects on the compliers, whose mediator reacts to the treatment. In our empirical application, we analyze the impact of the Vietnam draft lottery on political preferences. The results suggest that a high draft risk due to the draft lottery outcome leads to an increase in mild preferences for the Republican Party, but has no effect on strong preferences for either party or on specific political attitudes. The increase in Republican support is mostly driven by the direct effect not operating through the mediator that is military service.     

The Use of Ratios to Compare Volatilities and VaRs

The riskiness of two investments can be compared by looking at the ratio of the respective Value-at-Risk's (VaRs) or the ratio of volatilities. The exact distribution of the ratio of two volatilities calculated from normal observations and an asymptotic confidence interval for the ratio of two VaRs is derived. A simulation study shows good coverage rates for ratios of VaRs calculated from observations from distributions commonly used to model logarithmic returns.     

A Necessary Power Divergence Type Family Tests of Multivariate Normality

In a recent article, Cardoso de Oliveira and Ferreira have proposed a multivariate extension of the univariate chi-squared normality test, using a known result for the distribution of quadratic forms in normal variables. In this article, we propose a family of power divergence type test statistics for testing the hypothesis of multinormality. The proposed family of test statistics includes as a particular case the test proposed by Cardoso de Oliveira and Ferreira. We assess the performance of the new family of test statistics by using Monte Carlo simulation. In this context, the type I error rates and the power of the tests are studied, for important family members. Moreover, the performance of significant members of the proposed test statistics are compared with the respective performance of a multivariate normality test, proposed recently by Batsidis and Zografos. Finally, two well-known data sets are used to illustrate the method developed in this article as well as the specialized test of multivariate normality proposed by Batsidis and Zografos.     

Improved population-based probability of developing cancer when direct estimates of the cancer-free population are available

Age-conditional probabilities of developing a first cancer represent the transition from being cancer-free to developing a first cancer. Natural inputs into their calculation are rates of first cancer per person-years alive and cancer-free. However these rates are not readily available because they require information on the cancer-free population. Instead rates of first cancer per person-years alive, calculated using as denominator the mid-year populations, available from census data, can be easily calculated from cancer registry data. Methods have been developed to estimate age-conditional probabilities of developing cancer based on these easily available rates per person-years alive that do not directly account for the cancer-free population. In the last few years models (Merrill et al., Int J Epidemiol 29(2):197-207, 2000; Mariotto et al., SEER Cancer Statistics Review, 2002; Clegg et al., Biometrics 58(3):684-688, 2002; Gigli et al., Stat Methods Med Res 15(3):235-253, 2006, and software (ComPrev:Complete Prevalence Software, Version 1.0, 2005) have been developed that allow estimation of cancer prevalence (DevCan: Probability of Developing or Dying of Cancer Software, Version 6.0, 2005). Estimates of population-based cancer prevalence allows for the estimation of the cancer-free population and consequently of rates per person-years alive and cancer-free. In this paper we present a method that directly estimates the age-conditional probabilities of developing a first cancer using rates per person-years alive and cancer-free obtained from prevalence estimates. We explore conditions when the previous and the new estimators give similar or different values using real data from the Surveillance, Epidemiology and End Results (SEER) program.     

Imputation of missing variance data using non-linear mixed effects modelling to enable an inverse variance weighted meta-analysis of summary-level longitudinal data: a case study

Missing variances, on the basis of the summary-level data, can be a problem when an inverse variance weighted meta-analysis is undertaken. A wide range of approaches in dealing with this issue exist, such as excluding data without a variance measure, using a function of sample size as a weight and imputing the missing standard errors/deviations. A non-linear mixed effects modelling approach was taken to describe the time-course of standard deviations across 14 studies. The model was then used to make predictions of the missing standard deviations, thus, enabling a precision weighted model-based meta-analysis of a mean pain endpoint over time. Maximum likelihood and Bayesian approaches were implemented with example code to illustrate how this imputation can be carried out and to compare the output from each method. The resultant imputations were nearly identical for the two approaches. This modelling approach acknowledges the fact that standard deviations are not necessarily constant over time and can differ between treatments and across studies in a predictable way.     

Welche privaten Veräußerungsgewinne sollten besteuert werden?

This paper analyses for various corporate tax systems whether the capital gains tax distorts investment decisions and how tax effects could eventually be neutralized. In case of the disposal of shares between private investors the capital gains tax, the corporate tax and the income tax on dividends induce a triple taxation. On the contrary, distributing cash via share repurchases instead of paying out dividends can lower the tax burden in a classical corporate tax system and a shareholder relief system respectively. These findings necessitate the differentiation between share repurchases and other realizations of stocks in order to establish a neutral capital gains tax. While the capital gains taxation on transactions between private investors has to be reduced, the taxation of share repurchases must be matched with the respective dividend taxation.     

Sample size considerations for Japanese patients in a multi‐regional trial based on MHLW guidance

Since the publication of the International Conference on Harmonization E5 guideline, new drug approvals in Japan based on the bridging strategy have been increasing. To further streamline and expedite new drug development in Japan, the Ministry of Health, Labour and Welfare, the Japanese regulatory authority, recently issued the ‘Basic Principles on Global Clinical Trials' guidance to promote Japan's participation in multi‐regional trials. The guidance, in a Q&A format, provides two methods as examples for recommending the number of Japanese patients in a multi‐regional trial. Method 1 in the guidance is the focus of this paper. We derive formulas for the sample size calculations for normal, binary and survival endpoints. Computations and simulation results are provided to compare different approaches. Trial examples are used to illustrate the applications of the approaches. Copyright © 2009 John Wiley & Sons, Ltd.     

The public problem of ‘Aboriginal gambling‘: winning the struggle for an urban space

Gambling by Aboriginal people is increasingly identified as a significant public problem in Australia, eliciting responses mainly concerned with measurement and harm minimisation. We adopt the utilitarian philosophy of John Dewey to critically examine the way this ‘problem’ is socially constructed. We recast our roles as pragmatic researcher‐activists in the ongoing struggle to have Aboriginal practices taken seriously We draw particularly on the work of a group of senior Yolnu Aboriginal consultants and re‐present their story of gambling alongside other research on the Aboriginal use of urban gambling spaces. This helps us develop a nuanced explication of the public problem, one that challenges existing discourses and proposed solutions. We identify an Aboriginal space being produced within existing casinos which is only supported reactively by government and casino owners, and met with anxiety by community service providers. We propose the radical idea of Aboriginal urban gambling venues as indicators of what is needed for a successful, state‐supported, socially inclusionary and non‐exploitative space for Aboriginal people, and what obstacles may stand in the way of achieving this. Through this process, we assess how, as participant researchers, we can help to reformulate of the public problem in a way that is more closely aligned to Aboriginal needs and aspirations.