Polls

Read the explanations of polling methodology from the Star Tribune and the New York Times.

Problems

1. Which is more likely to be understandable to the general public?

2. One poll says that `one can be 95% confident that error due to sampling will be no more than plus or minus four percentage points.' The other says that `In theory, in 19 out of 20 cases the results based on such samples will differ by no more than 3 percentage points in either direction by what would have been obtained by interviewing all adult Iowans.' These are both attempts to explain the concept of margin of error. Do they amount to the same thing? If not, which do you think is the more accurate description? Where do the and percent come from?

3. In an article describing the results of a poll assessing people's preference for either one or the other of two candidates, you are told the proportion favoring Candidate A, and the margin of error for this quantity. The newspaper, however, usually concentrates on the difference between the proportion favoring A and favoring B. What is the margin of error for this quantity?

4. How many peopls believe the murder charges against O. J. Simpson are probably true? USA Today reports the results of a Gallup poll showing that-well, you can read it yourself. After giving the fraction of people giving each of 5 possible responses, they report that the margin of error for the poll is plus or minus 4 percentage points. What could this mean?