But in a recent study they declared that forty percent of the tweets captured over a two-week period were "pointless babble."

VOA: special.2009.09.14

Now maybe you're right, that we could study that, in fact, more people are born in June period.

可能你说的对，调查那些没有患厌食症的人，实际上还是会发现大多数人都是6月出生的。

麻省理工公开课 - 计算机科学及编程导论课程节选

A cohort study means you take the same group of people and follow them every five years for that period of time.

定群研究意味着你只有一组研究对象,然后在研究期间每五年进行一次记录数据

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

The study involved forty-four traders and their profits and losses over a twenty-month period ending in two thousand seven.

VOA: special.2009.02.25

The study examined employment records for eight cities in Minnesota for a three-year period through two thousand six.

VOA: special.2009.05.27

They used information gathered over a period of 20 years, until 2003, in the Framingham Heart Study.

VOA: special.2009.01.21

The only difference is they have one period a day where they study Islam."

VOA: standard.2010.07.12