Epidemiological research studies address questions like, “If 1,000 people with type 2 diabetes were randomly allocated to four groups of 250 people that each received either no treatment (or a placebo), drug A, drug B, or drug C for ten years, how would it impact survival rates, and what, if any, complications and side effects would there be?” If the trial is conducted properly – it is large enough; people are allocated in a truly random way; and “blind” assessments of the outcomes are conducted – the results should be reliable.
流行病学研究回答类似于这样的问题：“如果1,000个患有2型糖尿病的人随机地分为四个组，每组250人并在十年的时间里分别不治疗（或使用安慰剂）、使用药物A、使用药物B和使用药物C，存活率将会受到什么影响？副作用和并发症（如有）情况又会如何？”如果实验设计合理——规模足够大、人群真正以随机方式分组、结果为“盲”测——那么其结果应该是可靠的。