Question

An October 2011 CBS News Poll on illegal immigrants interviewed 1012 randomly selected American adults. Of those in the sample, 688 said that they “oppose allowing the children of illegal immigrants to attend state college at the lower tuition rate of state residents.” Although the samples in national polls are not SRSs, they are similar enough that our method gives approximately correct confidence intervals.

a) Find the 99% confidence interval for the proportion of adults who “oppose allowing the children of illegal immigrants to attend state college at the lower tuition rate of state residents.”

b) Find the 95% confidence interval. Is the 95% confidence interval longer or shorter than the 99% confidence interval?

c) Find the margin of error for each confidence interval. (Hint: you do have enough information from the calculator output! Margin of error = (width of interval)/2.)

  What is the margin of error for the 99% confidence interval? What is the margin of error for the 95% confidence interval?

Answer 1