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Cheng  Yi; Berry  Donald A. 《Biometrika》2007,94(3):673-689
Optimal decision-analytic designs are deterministic. Such designsare appropriately criticized in the context of clinical trialsbecause they are subject to assignment bias. On the other hand,balanced randomized designs may assign an excessive number ofpatients to a treatment arm that is performing relatively poorly.We propose a compromise between these two extremes, one thatachieves some of the good characteristics of both. We introducea constrained optimal adaptive design for a fully sequentialrandomized clinical trial with k arms and n patients. An r-designis one for which, at each allocation, each arm has probabilityat least r of being chosen, 0 r 1/k. An optimal design amongall r-designs is called r-optimal. An r1-design is also an r2-designif r1 r2. A design without constraint is the special case r = 0and a balanced randomized design is the special case r = 1/k.The optimization criterion is to maximize the expected overallutility in a Bayesian decision-analytic approach, where utilityis the sum over the utilities for individual patients over a‘patient horizon’ N. We prove analytically thatthere exists an r-optimal design such that each patient is assignedto a particular one of the arms with probability 1 – (k – 1)r,and to the remaining arms with probability r. We also show thatthe balanced design is asymptotically r-optimal for any givenr, 0 r < 1/k, as N/n  . This implies that everyr-optimal design is asymptotically optimal without constraint.Numerical computations using backward induction for k = 2arms show that, in general, this asymptotic optimality featurefor r-optimal designs can be accomplished with moderate trialsize n if the patient horizon N is large relative to n. We alsoshow that, in a trial with an r-optimal design, r < 1/2,fewer patients are assigned to an inferior arm than when followinga balanced design, even for r-optimal designs having the samestatistical power as a balanced design. We discuss extensionsto various clinical trial settings.  相似文献   

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Community-equipoise and the ethics of randomized clinical trials   总被引:4,自引:0,他引:4  
Gifford F 《Bioethics》1995,9(2):127-148
This paper critically examines a particular strategy for resolving the central ethical dilemma associated with randomized clincial trials (RCTs) -- the "community equipoise" strategy (CE). The dilemma is that RCTs appear to violate a physician's duty to choose that therapy which there is most reason to believe is in the patient's best interest, randomizing patients even once evidence begins to favor one treatment. The community equipose strategy involves the suggestion that our judgment that neither treatment is to be preferred (that there obtains a state of "equipoise") is to be assessed according to a community rather than an individual standard. Thus, though a physician may personally believe that there is some reason to prefer one treatment, patients can legitimately be randomized if there remains disagreement in the community of medical professionals. Rationales in favor of this conception include the following: (i) medical knowledge is best understood as residing in the community, (ii) the judgments of others count as evidence, and so should change one's own opinion, (iii) subjects would not be better off outside the trial, and (iv) the point of any trial is the resolution of dispute in the medical community. I critically examine these rationales and argue that they are insufficient. Amongst the problems are tensions between various of these underlying rationales, and important ambiguities in just what the CE criterion is to amount to. Finally, I argue that even if use of CE was justified, it would not justify carrying out RCTs anywhere near long enough to discharge our duty to gain reliable knowledge on which to base safe and effective medical practice. Hence, we need some different justification for carrying out RCTs.  相似文献   

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Tests for no treatment effect in randomized clinical trials   总被引:1,自引:0,他引:1  
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We examine stochastic inequality probabilities of the form P (X > Y) and P (X > max (Y, Z)) where X, Y, and Z are random variables with beta, gamma, or inverse gamma distributions. We discuss the applications of such inequality probabilities to adaptively randomized clinical trials as well as methods for calculating their values.  相似文献   

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Introduction

Patient adherence to therapy in clinical practice is often low, and the difference between efficacy measured in clinical trials and effectiveness in clinical practice is probably a function of discontinuation of therapy because of lack of efficacy or because of unmanageable or intolerable adverse events. Discontinuation is frequently measured in clinical trials but is not usually described in detail in published reports, often because of limitations in the size of publications. By contrast, company clinical trial reports include much more detail.

Methods

We examined company clinical trial reports of trials involving etoricoxib in four musculoskeletal conditions: osteoarthritis, rheumatoid arthritis, chronic low back pain and ankylosing spondylitis. Information was available from 18 randomized trials (10,143 patients) lasting 4 to 12 weeks (one 4 weeks, three 6 weeks, one 8 weeks and seven 12 weeks) and from three trials with a mean duration of about 80 weeks (34,695 patients). These clinical trial reports contain over 73,000 pages of information.

Results

Over 12 weeks, lack of efficacy and adverse event discontinuations were similar between osteoarthritis, rheumatoid arthritis and back pain, with lack of efficacy discontinuation rates some three times higher than for adverse events. All-cause and lack of efficacy discontinuations were lower with etoricoxib (all doses combined) and traditional nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) than with placebo, although NSAIDs produced higher rates of clinical adverse events and gastrointestinal discontinuations than did placebo. Etoricoxib had fewer discontinuations than NSAIDs for lack of efficacy, clinical adverse events, and laboratory and gastrointestinal adverse events, but with more discontinuations because of hypertension and oedema. Comparison with two similar meta-analyses of other cyclo-oxygenase-2 selective inhibitors (more than 80,000 patients in total) revealed consistency between analyses.

Conclusion

Examining discontinuation data from clinical trials, even when the numbers of patients are very large, does not necessarily predict what will happen in the real world, where clinical effectiveness may differ from clinical efficacy assessed in trials. Data from these analyses appears to agree with findings from real world practice.  相似文献   

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Zhang M  Tsiatis AA  Davidian M 《Biometrics》2008,64(3):707-715
Summary .   The primary goal of a randomized clinical trial is to make comparisons among two or more treatments. For example, in a two-arm trial with continuous response, the focus may be on the difference in treatment means; with more than two treatments, the comparison may be based on pairwise differences. With binary outcomes, pairwise odds ratios or log odds ratios may be used. In general, comparisons may be based on meaningful parameters in a relevant statistical model. Standard analyses for estimation and testing in this context typically are based on the data collected on response and treatment assignment only. In many trials, auxiliary baseline covariate information may also be available, and it is of interest to exploit these data to improve the efficiency of inferences. Taking a semiparametric theory perspective, we propose a broadly applicable approach to adjustment for auxiliary covariates to achieve more efficient estimators and tests for treatment parameters in the analysis of randomized clinical trials. Simulations and applications demonstrate the performance of the methods.  相似文献   

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Perhaps the most unpleasant experience following outpatient plastic surgery procedures is postoperative nausea and vomiting. Postoperative nausea and vomiting often results in delayed recovery time and unintended admission, and it can be a contributing factor to the formation of hematoma following rhytidectomy. Ondansetron (Zofran) has proven benefit in preventing postoperative nausea and vomiting if given before general anesthesia in a variety of surgical procedures. Its utility in cases performed under conscious sedation has not been determined. The purpose of this study was (1) to test the ability of prophylactic ondansetron to prevent postoperative nausea and vomiting in plastic surgery cases performed under conscious sedation, and (2) to determine relative risk factors for postoperative nausea and vomiting and a selection policy for the administration of antiemetic prophylaxis. This was a prospective, randomized, double-blind study. One hundred twenty patients were enrolled after giving informed consent. Patients received a single dose of either placebo or ondansetron (4 mg intravenously) before administration of sedation. Sedation administration followed a standardized institutional protocol, using midazolam and fentanyl. Data were recorded from a series of three questionnaires: preoperatively, immediately postoperatively, and at the time of the first office return. Data were confirmed by means of telephone interview, chart analysis, and nursing documentation. Multivariate analysis was conducted. Nausea and emesis occurred with an overall frequency of 33 percent and 22 percent, respectively. Postoperative nausea and vomiting was associated with statistically longer recovery periods. The incidence of emesis was statistically higher among women, among those undergoing facial rejuvenation, and among those with a history of opioid-induced emesis or postoperative nausea and vomiting following a previous operation (p < 0.05). The incidence of postoperative nausea and vomiting paralleled increases in case duration; the incidence of emesis was zero in cases less than 90 minutes in duration. Ondansetron significantly reduced the incidence of emesis overall (placebo, 30 percent; ondansetron, 13 percent; p < 0.05). Postoperative perception of nausea was significantly lower among those who had received ondansetron (p < 0.05). These results confirm the efficacy of ondansetron for the prevention of postoperative nausea and vomiting in plastic surgery cases under conscious sedation. In those who are at increased risk, prophylaxis should be considered. Such risks include female gender, facial rejuvenation procedures, and a patient history of opioid-induced emesis or postoperative nausea and vomiting following a prior operation. The zero incidence of emesis in cases less than 90 minutes does not support the routine use of prophylaxis in such cases. Patient satisfaction in plastic surgery is derived from the overall subjective experience of the event as much as by the final result. By remaining attentive to patient concerns and optimizing perioperative care, we can improve the subjective experience for our patients.  相似文献   

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Yin G  Shen Y 《Biometrics》2005,61(2):362-369
Clinical trial designs involving correlated data often arise in biomedical research. The intracluster correlation needs to be taken into account to ensure the validity of sample size and power calculations. In contrast to the fixed-sample designs, we propose a flexible trial design with adaptive monitoring and inference procedures. The total sample size is not predetermined, but adaptively re-estimated using observed data via a systematic mechanism. The final inference is based on a weighted average of the block-wise test statistics using generalized estimating equations, where the weight for each block depends on cumulated data from the ongoing trial. When there are no significant treatment effects, the devised stopping rule allows for early termination of the trial and acceptance of the null hypothesis. The proposed design updates information regarding both the effect size and within-cluster correlation based on the cumulated data in order to achieve a desired power. Estimation of the parameter of interest and its confidence interval are proposed. We conduct simulation studies to examine the operating characteristics and illustrate the proposed method with an example.  相似文献   

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Taylor L  Zhou XH 《Biometrics》2009,65(1):88-95
Summary .  Randomized clinical trials are a powerful tool for investigating causal treatment effects, but in human trials there are oftentimes problems of noncompliance which standard analyses, such as the intention-to-treat or as-treated analysis, either ignore or incorporate in such a way that the resulting estimand is no longer a causal effect. One alternative to these analyses is the complier average causal effect (CACE) which estimates the average causal treatment effect among a subpopulation that would comply under any treatment assigned. We focus on the setting of a randomized clinical trial with crossover treatment noncompliance (e.g., control subjects could receive the intervention and intervention subjects could receive the control) and outcome nonresponse. In this article, we develop estimators for the CACE using multiple imputation methods, which have been successfully applied to a wide variety of missing data problems, but have not yet been applied to the potential outcomes setting of causal inference. Using simulated data we investigate the finite sample properties of these estimators as well as of competing procedures in a simple setting. Finally we illustrate our methods using a real randomized encouragement design study on the effectiveness of the influenza vaccine.  相似文献   

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Lu X  Hongcai S  Jiaying W  Jing H  Jun X 《PloS one》2011,6(2):e16922

Objective

To evaluate the reports'' qualities which are about randomized controlled trials (RCTs) of acupuncture treatment on Mild Cognitive Impairment (MIC).

Methods

Nine databases including the Cochrane Central Register of Controlled Trials (CENTRAL,2010), PUBMED (1984-5/2010), EMbase (1984-5/2010), MEDLINE (1984-5/2010), CINAL (1984-5/2010), China National Knowledge Infrastructure (CNKI, 1980-5/2010), China Biomedicine Database disc (CBMdisc, 1980-5/2010), VIP (a full text issues database of China, 1989-5/2010) were searched systematically. Hand search for further references was conducted. Language was limited to Chinese and English. We identified 14 RCTs that used acupuncture as an intervention and assessed the quality of these reports against the Consolidated Standards for Reporting of Trials (CONSORT) statement and Standards for Reporting Interventions in Controlled Trials of Acupuncture (STRICTA).

Results

In regard to the items in the CONSORT statement, 13(92.86%) RCTs described baseline demographic and clinical characteristics in each group. 7 (50.0%) mentioned the method of generating the random sequence, only 2 (14.3%) RCTs had adequate allocation concealment. No RCTs used blinding. RCTs reported the sample size calculation. In regard to the items in STRICTA, 10 (71.43%) mentioned the depths of insertion, 6 (42.86%) reported acupuncture response, 11 (78.57%) mentioned the technique of acupuncture, 12 (85.71%) recorded the time, and only 3 (21.43%) RCTs reported the numbers of needles inserted. No RCTs reported the background of the acupuncture practitioners and professional title of practitioners.

Conclusion

The reporting quality of RCTs of acupuncture for mild cognitive impairment was moderate to low. The CONSORT statement and STRICTA should be used to standardize the reporting of RCTs of acupuncture in future.  相似文献   

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Defining the target population based on predictive biomarkers plays an important role during clinical development. After establishing a relationship between a biomarker candidate and response to treatment in exploratory phases, a subsequent confirmatory trial ideally involves only subjects with high potential of benefiting from the new compound. In order to identify those subjects in case of a continuous biomarker, a cut-off is needed. Usually, a cut-off is chosen that resulted in a subgroup with a large observed treatment effect in an exploratory trial. However, such a data-driven selection may lead to overoptimistic expectations for the subsequent confirmatory trial. Treatment effect estimates, probability of success, and posterior probabilities are useful measures for deciding whether or not to conduct a confirmatory trial enrolling the biomarker-defined population. These measures need to be adjusted for selection bias. We extend previously introduced Approximate Bayesian Computation techniques for adjustment of subgroup selection bias to a time-to-event setting with cut-off selection. Challenges in this setting are that treatment effects become time-dependent and that subsets are defined by the biomarker distribution. Simulation studies show that the proposed method provides adjusted statistical measures which are superior to naïve Maximum Likelihood estimators as well as simple shrinkage estimators.  相似文献   

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N L Geller  S J Pocock 《Biometrics》1987,43(1):213-223
Recent developments in group sequential methods have had a great impact on the design and analysis of randomized clinical trials. The consequences for both planned and unplanned interim analyses are discussed using several real trials as illustrations. Guidelines for the conduct of interim analysis are given, including tables of nominal significance levels and required sample sizes for several group sequential plans. Areas in need of further theoretical advance include multiple endpoints, estimation of treatment differences, stratification, and design of multiple-armed trials.  相似文献   

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