This paper considers testing the unit root hypothesis against a smooth transition autoregressive model as the alternative. The model specification makes it possible to discriminate between nonstationary random walk and stationary nonlinear processes. Some new limit results are presented,...

We performed a cross-sectional, "bottom-up" observational study of resource consumption and quality of life of patients with multiple sclerosis (MS) in the United Kingdom. Three centers participated in the study. Patients received a questionnaire either by mail or during a clinic visit, and a...

We performed a cross-sectional, "bottom-up" observational study of resource consumption and quality of life of patients with multiple sclerosis (MS) in Germany. Six centers participated in the study. Patients were asked to complete a questionnaire, and a total of 737 patients returned the...

OBJECTIVE: This article examines whether there are differences in men's and women's use of the Internet and whether any such gender gaps have changed in recent years. METHODS: We use data from several surveys during the period 1997 to 2001 to show trends in Internet usage and to estimate...

This paper contains a Lagrange multiplier test of the hypothesis that the covariance matrix of a multivariate time series model is constant over time. It is further assumed that under the alternative, the error variances are time-varying whereas the correlation remain constant over time. Under...