Choice of the primary analysis in longitudinal clinical trials

Missing data, and the bias they can cause, are an almost ever‐present concern in clinical trials. The last observation carried forward (LOCF) approach has been frequently utilized to handle missing data in clinical trials, and is often specified in conjunction with analysis of variance (LOCF ANOVA) for the primary analysis. Considerable advances in statistical methodology, and in our ability to implement these methods, have been made in recent years. Likelihood‐based, mixed‐effects model approaches implemented under the missing at random (MAR) framework are now easy to implement, and are commonly used to analyse clinical trial data. Furthermore, such approaches are more robust to the biases from missing data, and provide better control of Type I and Type II errors than LOCF ANOVA. Empirical research and analytic proof have demonstrated that the behaviour of LOCF is uncertain, and in many situations it has not been conservative. Using LOCF as a composite measure of safety, tolerability and efficacy can lead to erroneous conclusions regarding the effectiveness of a drug. This approach also violates the fundamental basis of statistics as it involves testing an outcome that is not a physical parameter of the population, but rather a quantity that can be influenced by investigator behaviour, trial design, etc. Practice should shift away from using LOCF ANOVA as the primary analysis and focus on likelihood‐based, mixed‐effects model approaches developed under the MAR framework, with missing not at random methods used to assess robustness of the primary analysis. Copyright © 2004 John Wiley & Sons, Ltd.     

Bias Correction in the Dynamic Panel Data Model with a Nonscalar Disturbance Covariance Matrix

Approximation formulae are developed for the bias of ordinary and generalized Least Squares Dummy Variable (LSDV) estimators in dynamic panel data models. Results from Kiviet [Kiviet, J. F. (1995), on bias, inconsistency, and efficiency of various estimators in dynamic panel data models, J. Econometrics68:53-78; Kiviet, J. F. (1999), Expectations of expansions for estimators in a dynamic panel data model: some results for weakly exogenous regressors, In: Hsiao, C., Lahiri, K., Lee, L-F., Pesaran, M. H., eds., Analysis of Panels and Limited Dependent Variables, Cambridge: Cambridge University Press, pp. 199-225] are extended to higher-order dynamic panel data models with general covariance structure. The focus is on estimation of both short- and long-run coefficients. The results show that proper modelling of the disturbance covariance structure is indispensable. The bias approximations are used to construct bias corrected estimators which are then applied to quarterly data from 14 European Union countries. Money demand functions for M1, M2 and M3 are estimated for the EU area as a whole for the period 1991: I-1995: IV. Significant spillovers between countries are found reflecting the dependence of domestic money demand on foreign developments. The empirical results show that in general plausible long-run effects are obtained by the bias corrected estimators. Moreover, finite sample bias, although of moderate magnitude, is present underlining the importance of more refined estimation techniques. Also the efficiency gains by exploiting the heteroscedasticity and cross-correlation patterns between countries are sometimes considerable.     

Tomb, temple, machine and self: the social construction of the body.

The body is socially constructed; and in this paper we explore the various and ever-changing constructions of the body, and thus of the embodied self, from the Greeks to the present. The one word, body, may therefore signify very different realities and perceptions of reality; and we consider briefly how and why these meanings changed. Plato believed the body was a 'tomb', Paul said it was the 'temple' of the Holy Spirit, the Stoic philosopher Epictetus taught that it was a 'corpse'. Christians believed, and believe, that the body is not only physical, but also spiritual and mystical, and many believed it was an allegory of church, state and family. Some said it was cosmic: one with the planets and the constellations. Descartes wrote that the body is a 'machine', and this definition has underpinned biomedicine to this day; but Sartre said that the body is the self. In sum, the body has no intrinsic meaning. Populations create their own meanings, and thus their own bodies; but how they create, and then change them, and why, reflects the social body.     

BURR CRITICAL VALUE APPROXIMATIONS FOR TESTS OF AUTOCORRELATION AND HETEROSCEDASTICITY

The paper evaluates the accuracy of Burr approximations of critical values and p-values for test a of autocorrelation and heteroscedasticity in the linear regression model.     

The Pyramid Model: A Useful Tool in Career Counseling With University Students

Often university students are faced with career decisions and seek help from the university counseling center. The pyramid model is a useful tool to assist the counselor and the student in the decision-making process. The metaphor enables the student to understand the tasks that lie ahead in the career counseling process. It is holistic. A case study is included to illustrate the three-dimensional model of career counseling of university students.     

Earnings Inequality in the Nonmetropolitan United States: 1967–19901

Abstract Nonmetropolitan (nonmetro) inequality patterns are contrasted with those of metropolitan (metro) areas to assess the utility of neoclassical and restructuring theoretical frameworks. Inequality measures are constructed from March Current Population Surveys for the years 1968–1991. Results indicate that inequality is greater in nonmetro areas than in metro areas. Results of decomposition procedures suggest that the observed inequality is due to a mix of neoclassical and restructuring factors that account for more inequality in metro than nonmetro areas. National policies must take account of metro/nonmetro differences in patterns and sources of inequality.     

Campus attitudes toward alcohol and drugs in a deep southern university.

In our zeal to deal with alcohol and drug abuse, we may have a distorted picture of what the majority of college students actually think about alcohol and drug use. Students in this study done at a public university located in the Deep South report being generally intolerant of substance abuse.