George W. Williams

Effect of Nandrolone Decanoate on the Anemia of Chronic Hemodialysis Patients

A double-blind cross-over study was conducted on 21 patients on maintenance hemodialysis to determine if changes in serum erythropoietin level, packed cell volume, red cell mass, hemoglobin concentrat

Number of observations required for the comparison of two correlated proportions

Previous sample size tables for studies with pairwise matching of experimental units and all-or-none responses have relied upon asymptotic results for the power function given the effective sample size of the experiment. In this paper the exact power function is employed to construct detailed sample size tables for such studies.

Rotavirus and reovirus stability in microorganism-free distilled and wastewaters

Survival of calf rotavirus and reovirus under controlled laboratory conditions in micro- organism-free, distilled and wastewater at 8 and 26°C was examined by periodic measurement of cyto- pathic effects (CPE) and indirect fluorescent antibody (IFA) assays. Five samples of both water-types were collected and inoculated with the two viruses. Three samples of each type of water were divided into two bottles, one per virus, for incubation at 8°C. Two samples were used at 26°C, one per trial. In the absence of light and shaking at 26°C, 7 13 days were required for a loss of 90~o infectivity for rotavirus and reovirus, while at 8°C, averages were 80 days for rotavirus and 260 days for reovirus. Virus infectivity remained for more than 30 days at 26°C and 400 days at 8°C. Rates of decline were 10-100 times greater at 26 than at 8°C, but at both temperatures, the MPN log10 rate of decline of infectivity was linear.

Asymptotically optimal sequential estimation of regular functionals of several distributions based on generalized U-statistics☆

For the several sample problem, a vector of estimable parameters is considered. For a fixed total sample size, a multistage (sequential) procedure based on generalized U-statistics is developed for choosing a partition of this sample size into individual sample size for which the generalized variance of the estimator of the parameter vector is asymptotically minimized.

Loss of infectivity of poliovirus 1 in river water under simulated field conditions

Abstract The effects of light, virus concentration, and turbidity on the rate of loss of infectivity (LOI) of poliovirus 1 were investigated in two test systems, which utilized flowing river water. Two levels of each variable were used in a 23 confounded factorial design. The seeded systems were sampled at regular intervals to establish LOI rates. Virus infectivity was measured by plaque assay. Loss of infectivity followed a two-component curve; an initial, rapid phase followed by a second, slower component. The slopes of the two components were examined by the analysis of variance to determine the potential influence of each variable. Both light and turbidity exerted a significant influence on the LOI rate in the second component of the LOI curve and also in the transition period between the two components; however, during the initial, rapid phase none of the variables influenced the LOI rate (at the 0.05 significance level). This research demonstrates the significance of light as a virucidal component in the aquatic environment.

On bounded maximum width sequential confidence ellipsoids based on generalized U-statistics

For a vector of (estimable) functionals of several independent distributions, sequential confidence ellipsoids (of bounded maximum width) based on a class of generalized U-statistics are studied. A stopping rule along with a procedure for choosing the component sample sizes at each stage is developed, so that the proposed confidence ellipsoid has a confidence coefficient asymptotically (as the prescribed maximum width shrinks to zero) equal to a preassigned 1 - [alpha] (0

Biochemical profiles during a Michigan heat wave: Suggestion of nutritional disturbance

Biochemical profiles routinely collected at a university clinic from 631 outpatients during a July Michigan heat wave and from 698 outpatients during a preceding cool period in June showed a statistically significant shift in the vector of means for 17 biochemical variables. The shift in mean values of two essential electrolytes (potassium and calcium) was significantly lower in two of the four age‐sex groups studied. While these departures are not significant by ordinary clinical standards for individual patients, they are unlikely to occur by chance. The data are consistent with, but not proof of, the hypothesis that changes in dietary levels of essential minerals such as potassium and calcium may be associated with heat waves. Poorly balanced meals (tea and toast, beer and pretzels) are probably more widely consumed during hot, humid weather than during normal seasonal conditions and provide a target for preventive measures. Physicians should be alert for early and reversible signs of potassium depleti...

A pilot Monte Carlo study of two sequential estimation procedures based on generalized U-statistics

Recently two sequential estimation procedures based on generalized U-statistics have appeared in the statistical literature [Williams and Sen (1973, 1974)]. One of these procedures concerns the multi-sample problem of estimating a vector of parameters when the total sample size is fixed. The other procedure concerns the multi-sample problem of constructing a confidence ellipsoid of bounded maximum width for a vector of parameters. To supplement the asymptotic theory discussed in these earlier papers, a Monte Carlo study investigating the efficiency of these procedures for moderate sample sizes would be useful. This paper describes a preliminary Monte Carlo study utilizing a small number of replications and performed to provide information for the design of a more extensive study.