It was an observational study.

VOA: special.2009.09.01

Now the epidemiology studies are observational studies.

流行病学研究是观察性研究

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

So when you put these observational studies together with a 'gold standard' clinical trial, the findings are overwhelming."

VOA: standard.2010.07.21

"In the observational studies we found that some of the B vitamins, like folic acid,were beneficial."

VOA: standard.2010.06.17

"I think there have been some observational,smaller studies that suggested the same thing.

VOA: standard.2010.07.21