The stylized approach to unit root testing: neglected contributions and the cost of simplicity

Following Dickey & Fuller (1979) (DF), a stylized approach to the testing of the unit root hypothesis has emerged. Based upon the combined use of the DF test in its augmented t -ratio form and MacKinnon (1991) critical values, the approach has received widespread adoption due to the ease with which it can be applied. In this paper a number of departures from this "stylized approach', which do not significantly reduce its ease of application, are examined. The results obtained from an empirical application to UK industrial production and Monte Carlo experimentation have clear methodological implications, showing that routine application of the stylized approach can lead to misleading inferences concerning the integrated nature of economic time series.     

Failure time studies with intermittent observation and losses to follow-up

In health research interest often lies in modeling a failure time process but in many cohort studies failure status is only determined at scheduled assessment times. While the assessment times may be fixed upon study entry, individuals may become lost to follow-up and miss visits subsequent to the time of loss to follow-up. We consider a three-state model to characterize a joint failure and loss to follow-up process, and use it to investigate the impact of dependent loss to follow-up on standard parametric, nonparametric, and semiparametric analysis. The effect of dependent loss to follow-up is mitigated by fitting the joint model. The performance of standard methods is studied using the asymptotic theory of misspecified models, and the finite sample performance is examined for the standard and joint analyses through simulation studies. An application to data from a youth smoking prevention study is presented for illustration.     

Copula-based score test for bivariate time-to-event data,with application to a genetic study of AMD progression

Lifetime Data Analysis - Motivated by a genome-wide association study to discover risk variants for the progression of Age-related Macular Degeneration (AMD), we develop a computationally efficient...     

A Study of Statistical Aspects of the Love Canal Environmental Monitoring Study

A major study released in May 1982 by the U.S. Environmental Protection Agency (EPA), in conjunction with the U.S. Department of Health and Human Services, concluded that a residential area surrounding the Love Canal chemical waste dump site exhibited no clear evidence of Canal-related contamination. Considering EPA study design and statistical methods used in data interpretation, we have reservations regarding the conclusions drawn from the study by the EPA and others. Our reservations focus mainly on the high likelihood of achieving only low power for detecting differences in chemical prevalence between the three sampling areas identified in the study. It is our conclusion that no decision can be reached concerning habitability of this area until a more comprehensive study is completed.     

Utilizing research in professional practice

A review of the rehabilitation, disability studies, and allied health literature suggests the presence of numerous factors that impede the utilization of research by practitioners. The purpose of this article is to describe these factors and offer potential solutions that could enable rehabilitation professionals to integrate research findings into their practice. Specifically, the authors recommend strategies to (a) contextualize research throughout pre-service curricula, (b) establish researcher-stakeholder partnerships, (c) increase the accessibility of research to practitioners, and (d) establish professional and peer support for implementing research in field practice.     

Patients' race, ethnicity, language, and trust in a physician

We examine whether racial/ethnic/language-based variation in measured levels of patients' trust in a physician depends on the survey items used to measure that trust. Survey items include: (1) a direct measure of patients' trust that the doctor will put the patient's medical needs above all other considerations, and (2) three indirect measures of trust asking about expectations for specific physician behaviors, including referring to a specialist, being influenced by insurance rules, and performing unnecessary tests. Using a national survey, we find lower scores on indirect measures of trust in a physician among minority users of health care services than among non-Hispanic white users. In contrast, the direct measure of trust does not differ among non-Hispanic whites and nonwhites once we control for potential confounding factors. The results indicate that racial/ethnic/language-based differences exist primarily in those aspects of patients' trust in a physician that reflect specific physician behaviors.     

Official statistics and UK elections

Len Cook , the UK's National Statistician, offers a personal view on the previous article by his counterpart in Norway.