Clinical trials : journal of the Society for Clinical Trials
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Recently, the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial published 7-year complete prostate cancer mortality results, which showed no benefit of screening with prostate specific antigen (PSA) and digital rectal examination (DRE). An issue of concern was the substantial level of 'contamination', or use of PSA and DRE in control arm men. ⋯ Use of prostate screening by control arm men was substantial, but also substantially less than in screened arm men. Detailed quantitative analyses of screening use across arms are critical for understanding current and future findings from the prostate component of PLCO.
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In an ongoing multi-center randomized control clinical trial, the Carotid Occlusion Surgery Study (COSS), the study protocol specifies multiple interim analyses whose results will be reviewed by an independent DSMB to determine if the trial needs to be stopped early due to either efficacy or futility. Conditional power is used as the decision rule for the DSMB to recommend stopping the trial for futility. An aggressive rule for futility stopping sets a relatively high threshold for the conditional power which may result in significant loss of overall power of the study. A conservative rule using a lower threshold may not be able to stop the trial early when there is indeed no treatment efficacy. ⋯ The proposed conditional power method facilitates a flexible futility monitoring plan that can be easily implemented in long-term clinical trials where multiple interim analyses are required. It provides the DSMB an objective guideline to use in considering early stopping for futility. Clinical Trials 2010; 7: 209. http:// ctj.sagepub.com.
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Randomized Controlled Trial
Motivating the unmotivated for health behavior change: a randomized trial of cessation induction for smokers.
Many smokers remain unwilling or unable to make a quit attempt. For these smokers, novel strategies to induce quit attempts are necessary to achieve further reductions in smoking prevalence. ⋯ The study has translational potential to guide both clinical and policy recommendations for cessation induction. Further, while the focus is on smoking, this trial may serve as an example to researchers and clinicians who focus on other health behaviors, and who themselves are challenged with motivating people who are unmotivated for change.
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Benign prostatic hyperplasia (BPH), a common condition among older men, confers its morbidity through potentially bothersome lower urinary tract symptoms. Treatments for BPH include drugs such as alpha-adrenergic receptor blockers and 5-alpha reductase inhibitors, minimally invasive therapies that use heat to damage or destroy prostate tissue, and surgery including transurethral resection of the prostate. Complementary and alternative medicines are gaining popularity in the US. Two phytotherapies commonly used for BPH are extracts of the fruit of Serenoa repens, the Saw palmetto dwarf palm that grows in the Southeastern US, and extracts of the bark of Pygeum africanum, the African plum tree. ⋯ Trial design occurs in an environment of continually evolving information. In this case, emerging results from another trial suggested that a study of long-term efficacy was premature, and that an effective dose and preparation of S. repens had to be established before proceeding to a long-term clinical trial.
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It is highly desirable to terminate a clinical trial early if the emerging data suggests that the experimental treatment is ineffective, or substantially less effective than the level the study was designed to detect. Many studies have used a conditional power calculation as the basis for termination for futility. However, in order to compute conditional power one must posit an assumption about the distribution of the future data yet to be observed, such as that the original design assumptions will apply, or that the future data will have the same treatment effect as that estimated from the current 'trend' in the data. Each such assumption will yield a different conditional power value. ⋯ These methods allow the design of clinical trials that have specified operating characteristics with a pre-specified futility analysis based only on the interim quantities that have been observed. Examples are presented.