He says studies on the effectiveness of nurse practitioners have been too small to be conclusive.

VOA: standard.2010.05.14

Then, they did preliminary studies of safety and effectiveness in people.

接着,研究人员对疫苗在人体中的,安全性和有效性进行初步研究

耶鲁公开课 - 生物医学工程探索课程节选

Then, they did preliminary studies of safety and effectiveness in people.

接着,研究人员对疫苗在人体中的,安全性和有效性进行初步研究

耶鲁公开课 - 生物医学工程探索课程节选