Class 23:  Confidence Intervals


Discussion 1


Read the article “Many in U.S. Want Texting at the Wheel to Be Illegal” from the New York Times.


1)    The article says that 50% of the people polled said that the punishment for texting while driving should be as severe as for drunken driving.  What do you think?

2)    Attach a standard error to this estimate of 50%.  Also calculate two times the standard error. 

3)    At the end of the article, it says that the poll has a “margin of sampling error of plus or minus 3 percentage points.  How does 3 percentage points compare to the standard error you calculated?  How does it compare to twice the standard error?

4)    This is how the New York Times explains the “margin of error” of 3 percentage points, in the side article “How the Poll was Conducted”:


“In theory, in 19 cases out of 20, overall results based on such samples will differ by no more than 3 percentage points in either direction from what would have been obtained by seeking to interview all American adults.”


What is 19/20 as a percent?    What do you think the New York Times means?     


Discussion 2


What percent of beans in the bowl are white beans?  Take a sample and make an estimate. What range would you give with 95% confidence for percent of white beans in the bowl?  Write your estimate and 95% confidence interval on the board, along with the number of beans in your sample. 

How would you estimate the total number of beans in the bowl?