关于自荐样本偏差的理解和疑问

深高金的zkk

Researchers recently asked dozens of shoppers, chosen at random coming out of a FoodBasket supermarket, what they had purchased. The prices of the very same items at the nearest ShopperKing supermarket were totaled and compared with the FoodBasket total. The ShopperKing totals averaged five percent higher than the FoodBasket totals. Nevertheless, this result does not necessarily show that shoppers at ShopperKing would save money overall by shopping at FoodBasket instead, since __________.
Ashoppers who shop regularly at a given supermarket generally choose that store for the low prices offered on the items that they purchase most often
Bfor shoppers with more than 20 items, the ShopperKing totals averaged more than five percent higher than the FoodBasket totals

Cmany shoppers consider factors other than price in choosing the supermarket at which they shop most regularly
Dthere is little variation from month to month in the overall quantity of purchases made at supermarkets by a given shopper
Enone of the people who conducted the research were employees of the FoodBasket supermarket
答案选A，但是我并不是很能理清楚里面的逻辑。A在说，古加尔更喜欢买他们经常买的东西，这个东西在他们经常去的超市比较便宜。换句话说：我喜欢在S买鸡腿肉，鸡腿肉的价格在S超市的比F超市的便宜。
原题目说same items在S的价格和F的价格进行比对后，S更贵。这个和原题目说same items的S的价格比F价格更贵，不矛盾嘛？

深高金的zkk

不知道我的理解对不对。调查者调查了F超市门口的人群。这些人群中，是因为他们买的东西相比于S超市，在F是更便宜的。"the ShpperKing totals averaged five percent higher than the FoodBasket totals"这个total说的是，这些被调查的人群买的商品，在S超市的总体平均比F更高。（不是S和F超市的全部商品）

mandy1991

深高金的zkk 发表于 2020-8-10 19:26
不知道我的理解对不对。调查者调查了F超市门口的人群。这些人群中，是因为他们买的东西相比于S超市，在F是 ...

是的。类似于在浦东机场检查从欧洲回来的旅客的行李箱，行李箱的东西在上海更贵，并不能说明上海的物价高于欧洲物价。因为人家去欧洲旅游肯定买欧洲便宜的东西