By contrast, her study is what is known as an observational study, where participants themselves decide, in this case, whether to take a fish oil supplement, and then the researchers observe them to see who develops cancer. But the women who chose to use a supplement could be different in many other ways from those who didn't.
她的研究方法与此相反，那是一种观察式的研究。由参与者自行选择要不要服用鱼油补充剂。然后研究人员观察她们，注意谁会患癌症。不过，选择服用鱼油补充剂的妇女，也可能和不服用鱼油的妇女，还有许多其它方面的不同。
White and her colleagues did try to factor those differences into their analysis, but scientists generally prefer a randomized study, and researchers at Harvard are now organizing one to study the effects of both omega-3 fatty acids and vitamin D.
怀特和她的同事们曾经尝试把各方面的不同因素纳入分析研究。不过，科学家们通常更愿意采用随机研究的方式。哈佛大学的研究人员也正在准备展开对欧米加-3 和维生素D的效果的研究。
White's paper is published in the journal Cancer Epidemiology, Biomarkers & Prevention.
