急——关于AP心理学 什么是group matching?

急——关于AP心理学 什么是group matching?
AP psychology里有group mathching 的概念,不是很懂诶
barronl有说Group matching would not result in the same number of males and females within each group.Rather,half of the males and half of the females would be in each of the groups.
ps.group matching 在中文里对应的概念叫什么?
感激不尽!