Right. Another way of saying it is there isn't random assignment of the subjects to the two conditions in the study.

换种方式说,受试者并不是随机安排在,这个研究中的两种情况下。

耶鲁公开课 - 心理学导论课程节选

Do I go out to Harvard yard and take a random sample ? of sophomores to study meditation?

是不是可以在哈佛大二学生里随机抽样,来研究冥想？

哈佛公开课 - 幸福课课程节选