Margin of ErrorMargin of Error

12-11-0812-11-08Ms. SiaMs. SiaIMP4IMP4

Today’s AgendaToday’s Agenda

Review problem from Tuesday Review problem from Tuesday (about City Hall)(about City Hall)

Polling Puzzles p. 434Polling Puzzles p. 434

AnnouncementsAnnouncements

Extra credit assignments can be Extra credit assignments can be found at the back of the book found at the back of the book from p. 445 to 454 (any of the from p. 445 to 454 (any of the Supplemental Problems)Supplemental Problems)

HW Hall today until 4:30pmHW Hall today until 4:30pm Pollster’s Dilemma Unit Test is Pollster’s Dilemma Unit Test is

next Thursday, December 18next Thursday, December 18thth

REMEMBERREMEMBER

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.

City HallCity Hall

Issue: City Hall decides to let Chicago’s Issue: City Hall decides to let Chicago’s homeless people sleep in City Hall at homeless people sleep in City Hall at night.night.

After taking a poll, a local newspaper finds After taking a poll, a local newspaper finds that 52% favor the plan, with a margin of that 52% favor the plan, with a margin of error of plus or minus 4%.error of plus or minus 4%.1.1. What is the confidence interval for this poll?What is the confidence interval for this poll?2.2. Explain what it means to say that the poll has a Explain what it means to say that the poll has a

95% confidence level.95% confidence level.3.3. How large is 2How large is 2? How large is ? How large is ??4.4. Approximately how many people were in the Approximately how many people were in the

sample?sample?

Polling Puzzles p. 434Polling Puzzles p. 434

When we don’t know p, what When we don’t know p, what should we assume?should we assume?

Show all your work, include Show all your work, include explanations IN WORDS.explanations IN WORDS.

Turn this in at the end of class.Turn this in at the end of class.