Estimate of the number of patients to enroll in a clinical trial - Project VALKYRIE

When we designed the Valkyrie trial several different considerations were made on how to calculate the number of patients to be recruited for the trial. In the end, the decision fell on the way as described in the project [methodology][meto] (translated from portuguese):<br> - #### 5.7.Sample size:<br> - The sample size does not depend on the initial question, which is not comparative. However, in order to ascertain secondary outcomes, it was necessary to calculate the expected number of patients to be recruited. Using data available from patients already treated in our hospital (as discussed above) as a pilot group, assuming a hazard ratio of 0.05 and choosing a statistical power of 80% and 0.5% alpha the minimum number of patients required in the experimental group (in a 1:2 design) is 16 patients. We expect to require 2 years to recruit this sample. The comparison group to be used will be the historic control group of patients treated at our institution between 2000 and 2013, with schemes other than HIT (number of patients 31, suitable for this experimental design). The powerSurvEpi package of R language was used to calculate the sample size (R Development Core Team, 2012).(excerpt)

在设计瓦尔基里（Valkyrie）临床试验时，我们针对该试验所需招募的患者数量计算方式展开了多维度考量。最终，我们选定了项目[方法论（methodology）][meto]（译自葡萄牙语）中所述的计算方式：
- 5.7 样本量：
本试验的样本量并不依赖于非对照性的初始研究问题。但为了明确次要结局指标，我们需要计算预期招募的患者总数。我们以本院既往收治患者的可用数据（如前文所述）作为预试验组，假设风险比（hazard ratio）为0.05，设定统计效能（statistical power）为80%、检验水准α为0.5%，按照1:2的分组设计，试验组所需的最小患者数量为16例。我们预计完成该样本招募需耗时2年。本次研究的对照组将采用本院2000年至2013年间收治的、未接受HIT治疗方案的患者历史对照队列（共31例患者，适配本试验设计）。本研究采用R语言的powerSurvEpi包完成样本量计算（R开发核心团队，2012）。（节选）