A randomized exploratory clinical trial comparing an experimental treatment with a control treatment on a binary endpoint is often conducted to make a go or no‐go decision. Such an exploratory trial needs to have an adequate sample size such that it will provide convincing evidence that the experimental treatment is either worthwhile or unpromising relative to the control treatment. In this paper, we propose three new sample‐size determination methods for an exploratory trial, which utilize the posterior probabilities calculated from predefined efficacy and inefficacy criteria leading to a declaration of the worthwhileness or unpromisingness of the experimental treatment. Simulation studies, including numerical investigation, showed that all three methods could declare the experimental treatment as worthwhile or unpromising with a high probability when the true response probability of the experimental treatment group is higher or lower, respectively, than that of the control treatment group. 相似文献
Poor self-rated health is considered to be a predictor of short survival, and self-rated health is associated with several lifestyle and sociodemographic factors. To determine whether marital status is an independent risk factor for poor self-rated health among inhabitants in rural areas, we conducted a cross-sectional survey of inhabitants in Japan. Complete responses were obtained from 10,268 individuals. Self-ratings of mental health, demographics, and symptoms were used to predict self-rated health. Being male; having disease, questionnaire-based physical complaints, and depressive state; having lower levels of education; and being divorced resulted in higher odds (95% confidence interval) for poor self-rated health, presenting 1.41 (1.18–1.69), 10.8 (8.62–13.7), 1.11 (1.09–1.12), 1.11 (1.08–1.13), 1.22 (1.02–1.46), and 1.53 (1.01–2.31), respectively. In contrast, age, friendship, and other marital status such as single or bereaved showed no significant relationship with poor self-rated health. To improve self-rated health among rural inhabitants, attention should be focused on divorced inhabitants, especially men. 相似文献
A binary relation is indifference-transitive if its symmetric part satisfies the transitivity axiom. We investigated the properties of Arrovian aggregation rules that generate acyclic and indifference-transitive social preferences. We proved that there exists unique vetoer in the rule if the number of alternatives is greater than or equal to four. We provided a classification of decisive structures in aggregation rules where the number of alternatives is equal to three. Furthermore, we showed that the coexistence of a vetoer and a tie-making group, which generates social indifference, is inevitable if the rule satisfies the indifference unanimity. The relationship between the vetoer and the tie-making group, i.e., whether the vetoer belongs to the tie-making group or not, determines the power structure of the rule. 相似文献
The relationship between fig trees and their pollinator wasps is a well-known example of species-specific obligate mutualism.
In this article we present a stochastic model of this mutualistic system, referring to data on a dioecious fig (Ficus schwarzii) in Borneo, and examine the conditions for the persistence of a wasp population for a given period. (1) When the average
duration of the flowering interval of fig trees is short, even a small fig population can sustain a wasp population successfully.
A population whose average period of flowering cycle is half that of another population can sustain a wasp population with
a number of trees less than half of the other population. (2) The wasp survival rate (WSR) is higher when (a) the variation
of the interval periods of fig flowering is smaller, (b) the fig population size is larger, and (c) figs can prolong their
receptivity to wait for a wasp if no wasps are available. (3) WSR is predictable from the average proportion of the fig's
receptive phases, in which wasps are available, to their total receptive phases. (4) The persistence period of a wasp population
increases exponentially with the number of fig trees. Based on these results we propose a new hypothesis, as a possible scenario,
on the evolution of dioecy from monoecy in Ficus.
Received: November 13, 1998 / Accepted: July 14, 1999 相似文献
We consider an incomplete markets economy with capital accumulation and endogenous labor supply. Individuals face countercyclical idiosyncratic labor and asset risk. We derive conditions under which the aggregate allocations and price system can be found by solving a representative agent problem. This result is applied to analyze the properties of an optimal monetary policy in a New Keynesian economy with uninsured countercyclical individual risk. The optimal monetary policy that emerges from our incomplete markets economy is the same as the optimal monetary policy in a representative agent model with preference shocks. When price rigidity is the only friction the optimal monetary policy calls for stabilizing the inflation rate at zero. 相似文献
We discuss the multivariate (2L-variate) correlation structure and the asymptotic distribution for the group-sequential weighted logrank statistics formulated when monitoring two correlated event-time outcomes in clinical trials. The asymptotic distribution and the variance–covariance for the 2L-variate weighted logrank statistic are derived as available in various group-sequential trial designs. These methods are used to determine a group-sequential testing procedure based on calendar times or information fractions. We apply the theoretical results to a group-sequential method for monitoring a clinical trial with early stopping for efficacy when the trial is designed to evaluate the joint effect on two correlated event-time outcomes. We illustrate the method with application to a clinical trial and describe how to calculate the required sample sizes and numbers of events.