Implementing and Documenting Random Number Generators

As simulation arid Monte Carlo continue to play an increasing role in statistical research, careful attention must be given to problems which arise in implementing and documenting collect ions of random number generators. This paper examines the value of theoretical as well as empirical evidence in establishing the quality of generators, the selection of generators to comprise a good basic set, the techniques and efficiency of implementation, and the extent of documentation. Illustrative examples are drawn from various current sources.

Monte Carlo Techniques in Studying Robust Estimators

Recent work on robust estimation has led to many procedures, which are easy to formulate and straightforward to program but difficult to study analytically. In such circumstances experimental sampling is quite attractive, but the variety and complexity of both estimators and sampling situations make effective Monte Carlo techniques essential. This discussion examines problems, techniques, and results and draws on examples in studies of robust location and robust regression.

Notes on Automating Stem and Leaf Displays

The stem-and-leaf display is a natural semi-graphic technique to include in statistical computing systems. This paper discusses the choices involved in implementing both automated and flexible versions of the display, develops an algorithm for the automated version, examines various implementation considerations, and presents a set of semi-portable FORTRAN subroutines for producing stem-and-leaf displays.

British Tea: Steeped in the Imperial Nation-State

In some regards, drinking tea has always been considered a British pastime. But, where, when, and how did tea take a hold of the nation to such an extent that a once considered Aristocratic luxury import became part of the commoner’s palate? Crucially, empire-building and nation-building have been mutually reinforcing for Britain, and tea is the lens through which one can understand the development of the imperial British nation-state. Tea became an entrenched symbol of British identity on both the national and imperial levels through a multiplicity of forces and actors. This thesis intends to prove that tea, through production and consumption methods, influenced conceptions of Britishness. In addition, this work will reveal the results of Britain imposing capitalism on the world, such as with its India colony, and explain that there are consequences largely unknown to the consumer when markets become separated from the rest of human activity (thus creating a broken \u27Wallersteinian\u27 commodity chain. This analysis presents a new approach to understanding the transformational seventeenth to nineteenth centuries which Britons deepened awareness of their roles in the global economy. Overall, even though tea is not such an innocent commodity due to its aggressive production methods, tea significantly contributed to Britishness at home and abroad

Estimation in meta-analyses of mean difference and standardized mean difference

Methods for random-effects meta-analysis require an estimate of the between-study variance, τ 2. The performance of estimators of τ 2 (measured by bias and coverage) affects their usefulness in assessing heterogeneity of study-level effects and also the performance of related estimators of the overall effect. However, as we show, the performance of the methods varies widely among effect measures. For the effect measures mean difference (MD) and standardized MD (SMD), we use improved effect-measure-specific approximations to the expected value of Q for both MD and SMD to introduce two new methods of point estimation of τ 2 for MD (Welch-type and corrected DerSimonian-Laird) and one WT interval method. We also introduce one point estimator and one interval estimator for τ 2 in SMD. Extensive simulations compare our methods with four point estimators of τ 2 (the popular methods of DerSimonian-Laird, restricted maximum likelihood, and Mandel and Paule, and the less-familiar method of Jackson) and four interval estimators for τ 2 (profile likelihood, Q-profile, Biggerstaff and Jackson, and Jackson). We also study related point and interval estimators of the overall effect, including an estimator whose weights use only study-level sample sizes. We provide measure-specific recommendations from our comprehensive simulation study and discuss an example

Estimation in meta-analyses of response ratios

BACKGROUND: For outcomes that studies report as the means in the treatment and control groups, some medical applications and nearly half of meta-analyses in ecology express the effect as the ratio of means (RoM), also called the response ratio (RR), analyzed in the logarithmic scale as the log-response-ratio, LRR. METHODS: In random-effects meta-analysis of LRR, with normal and lognormal data, we studied the performance of estimators of the between-study variance, τ2, (measured by bias and coverage) in assessing heterogeneity of study-level effects, and also the performance of related estimators of the overall effect in the log scale, λ. We obtained additional empirical evidence from two examples. RESULTS: The results of our extensive simulations showed several challenges in using LRR as an effect measure. Point estimators of τ2 had considerable bias or were unreliable, and interval estimators of τ2 seldom had the intended 95% coverage for small to moderate-sized samples (n<40). Results for estimating λ differed between lognormal and normal data. CONCLUSIONS: For lognormal data, we can recommend only SSW, a weighted average in which a study's weight is proportional to its effective sample size, (when n≥40) and its companion interval (when n≥10). Normal data posed greater challenges. When the means were far enough from 0 (more than one standard deviation, 4 in our simulations), SSW was practically unbiased, and its companion interval was the only option

Network Meta-Analysis of Ulcerative Colitis Pharmacotherapies: Carryover Effects from Induction and Bias of the Results

Dear Editor, In their network meta-analyses (NMAs) of treatments for ulcerative colitis (UC), Singh et al1 did not take into account a complication associated with studies that re-randomized patients for the maintenance phase: differential carryover effects from induction can bias the results. In those studies, patients who responded to induction were re-randomized to maintenance treatments that included placebo. If, however, carryover effects from induction differ substantially among active treatments, the effects of those treatments, relative to placebo, are not comparable