A consumer magazine plans to poll car owners to see if they are happy enough with their vehicles that they would purchase the same model again.
They'll randomly select 450 owners of American-made cars and 450 owners of Japanese models. Obviously, the actual opinions of the entire population couldn't be known, but suppose 76% of owners of American cars and 78% of owners of Japanese cars would purchase another.
a) What kind of sampling design is the magazine planning to use?
b) What difference would you expect their poll to show?
c) Of course, sampling error means the poll won't reflect the difference perfectly. What's the standard deviation for the difference in the proportions?
d) Sketch a sampling model for the difference in proportions that might appear in a poll like this.