It is well known to applied statisticians and scientists that the assumption of independence is often not valid for real data. In particular, even when all precautions are taken to prevent dependence, slowly decaying serial correlations frequently occur. If not taken into account, they can have disastrous effects on statistical inference. This phenomenon has been observed empirically by many prominent scientists long before suitable mathematical models were known. Apart from some scattered early references, mathematical models with long-range dependence were first introduced to statistics by Mandelbrot and his co-workers (Mandelbrot and Wallis, 1968, 1969; Mandelbrot and van Ness, 1968). Since then, long-range dependence in statistics has gained increasing attention. Parsimonious models with long memory are stationary increments of self-similar processes with self-similarity parameter $H \in (1/2,1)$, fractional ARIMA processes and other stationary stochastic processes with non-summable correlations. In the last decade, many results on statistical inference for such processes have been established. In the present paper, a review of these results is given.

In frequently occurring life-threatening diseases such as cancer, AIDS and cardiovascular disease, there is a need of significant public health importance for rapid yet reliable evaluation of promising new therapeutic interventions that might provide greater efficacy and reduced toxicity. Leadership from statistical scientists is essential to effectively address many of the challenges resulting from this need. By discussing recent experiences, primarily in the area of oncology and AIDS clinical trials, we will illustrate several of these challenges. We also will review some designs and methods that have been implemented in these settings. Particular attention will be given to experiences from involvement with FDA Advisory Committees and with Data Monitoring Committees for clinical trials sponsored by industry or by the National Institutes of Health. Among issues to be discussed will be the role of independent monitoring committees and group sequential guidelines in randomized clinical trials, the evaluation of equivalence trials and the use of surrogate and auxiliary endpoints.

The Gibbs sampler, the algorithm of Metropolis and similar iterative simulation methods are potentially very helpful for summarizing multivariate distributions. Used naively, however, iterative simulation can give misleading answers. Our methods are simple and generally applicable to the output of any iterative simulation; they are designed for researchers primarily interested in the science underlying the data and models they are analyzing, rather than for researchers interested in the probability theory underlying the iterative simulations themselves. Our recommended strategy is to use several independent sequences, with starting points sampled from an overdispersed distribution. At each step of the iterative simulation, we obtain, for each univariate estimand of interest, a distributional estimate and an estimate of how much sharper the distributional estimate might become if the simulations were continued indefinitely. Because our focus is on applied inference for Bayesian posterior distributions in real problems, which often tend toward normality after transformations and marginalization, we derive our results as normal-theory approximations to exact Bayesian inference, conditional on the observed simulations. The methods are illustrated on a random-effects mixture model applied to experimental measurements of reaction times of normal and schizophrenic patients.

Markov chain Monte Carlo using the Metropolis-Hastings algorithm is a general method for the simulation of stochastic processes having probability densities known up to a constant of proportionality. Despite recent advances in its theory, the practice has remained controversial. This article makes the case for basing all inference on one long run of the Markov chain and estimating the Monte Carlo error by standard nonparametric methods well-known in the time-series and operations research literature. In passing it touches on the Kipnis-Varadhan central limit theorem for reversible Markov chains, on some new variance estimators, on judging the relative efficiency of competing Monte Carlo schemes, on methods for constructing more rapidly mixing Markov chains and on diagnostics for Markov chain Monte Carlo.