1. Margin of Error 12-11-08 Ms. Sia IMP4

2. Today’s Agenda Review problem from Tuesday (about City Hall) Review problem from Tuesday (about City Hall) Polling Puzzles p. 434 Polling Puzzles p. 434

3. Announcements Extra credit assignments can be found at the back of the book from p. 445 to 454 (any of the Supplemental Problems) Extra credit assignments can be found at the back of the book from p. 445 to 454 (any of the Supplemental Problems) HW Hall today until 4:30pm HW Hall today until 4:30pm Pollster’s Dilemma Unit Test is next Thursday, December 18 th Pollster’s Dilemma Unit Test is next Thursday, December 18 th

4. REMEMBER   Margin of error is the “radius” of a confidence interval, or the distance that the interval extends in either direction from the mean. Confidence intervals can take on values that are non-integer multiples of  When margin of error is mentioned without mentioning the confidence interval, we should assume that it refers to a 95% confidence level.

5. City Hall Issue: City Hall decides to let Chicago’s homeless people sleep in City Hall at night. Issue: City Hall decides to let Chicago’s homeless people sleep in City Hall at night. After taking a poll, a local newspaper finds that 52% favor the plan, with a margin of error of plus or minus 4%. After taking a poll, a local newspaper finds that 52% favor the plan, with a margin of error of plus or minus 4%. 1. What is the confidence interval for this poll? 2. Explain what it means to say that the poll has a 95% confidence level. 3. How large is 2  ? How large is  ? 4. Approximately how many people were in the sample?

6. Polling Puzzles p. 434 When we don’t know p, what should we assume? When we don’t know p, what should we assume? Show all your work, include explanations IN WORDS. Show all your work, include explanations IN WORDS. Turn this in at the end of class. Turn this in at the end of class.