没讨论国，我搜索GWD17-Q30 - ChaseDream

In a study conducted in Pennsylvania, servers in various restaurants wrote “Thank you” on randomly selected bills before presenting the bills to their customers. Tips on these bills were an average of three percentage points higher than tips on bills without the message. Therefore, if servers in Pennsylvania regularly wrote “Thank you” on restaurant bills, their average income from tips would be significantly higher than it otherwise would have been.

Answer: B 为什么啊，不明白如果他们改掉了以前的小费习惯，受字条影响，那不是给的更多啊

以下是引用百草园Tracy在2008-10-1 18:25:00的发言：

答案B，取非，改回原来习惯，则没法提高收入

A,C,D无关选项

E为太过绝对化，绝对化选项不选

由一个调研中的结果，得出一个结论。题目铺垫的是取样方法是random，取样地点是various，取样人肯定也是中立的。貌似无懈可击，不需要前提了——不看几个答案根本想不到答案会是那个方面的。B答案谈到若是多次抽到一个样本，那么样本的特性还是随机的——不能有惯性了。

E所有看到"thank u"的顾客都会给更多小费，不是太绝对；否则改成49%就可以成为正确答案了？Assumption应该是这个因果结论推断中缺失的部分——未考虑到的因素——将调研对象态度限定这样的assumption不对。

以下是引用riverquiet在2007-9-30 11:07:00的发言：

没讨论国，我搜索了 . GWD17-Q30:

Which of the following is an assumption on which the argument relies?

The “Thank you” messages would have the same impact on regular patrons of a restaurant as they would on occasional patrons of the same restaurant.
Regularly seeing “Thank you” written on their bills would not lead restaurant patrons to revert to their earlier tipping habits.
The written “Thank you” reminds restaurant patrons that tips constitute a significant part of the income of many food servers.
The rate at which people tip food servers in Pennsylvania does not vary with how expensive a restaurant is.
Virtually all patrons of the Pennsylvania restaurants in the study who were given a bill with “Thank you” written on it left a larger tip than they otherwise would have.

Answer: B 为什么啊，不明白如果他们改掉了以前的小费习惯，受字条影响，那不是给的更多啊

原文说：出示账单前贴个感谢导致比不贴多3倍小费。所以贴了比不贴好。

A说感谢针对同样回头客（patron不认识就算了）在同样的饭店，离谱，杀！

E看到virtually all,心里一紧，问自己假设需要这么强的语气么？想起《大秦帝国》里面那句“望之不似人君”的motto