Rather, researchers “enrich” the study population by using a characteristic, such as age or laboratory-test results, to select a subset of patients in whom the intervention’s effects will likely be easier to detect than they would be in an unfiltered population. In recent years, “biomarkers,” such as certain DNA sequences or the presence of a particular drug receptor, have become increasingly important indicators for determining eligibility for clinical trials.
事实上，临床试验的宗旨并不是显示某种治疗（包括药物、医疗设备或其他干预方法）对普通人群中完全随机抽取的样本是否有效，相反，科研人员以年龄或实验室检查结果等某些特点来“浓缩”被研究群体，并从中筛选出比未经过滤人员更容易显示疗效的那部分患者。近年来，特定DNA序列或带有某种药物受体的“生物指标”已经成为确定临床试验资格的重要标准。