Public Opinion Polling

Chapter 6AP Government

History of Polling

• George Gallup – surveyed citizens of Iowa in 1936, where his mother was running for public office

• Was able to predict the outcome of the election, but not to the degree of accuracy he desired

• His method of quota sampling called the race within 4 percentage points; so he switched to probability sampling

Quota v. Probability Sampling

• Quota sampling uses a quota that reflects the actual population – for example if you survey both sexes, the percentages would roughly be 52% female and 48% male.

• Probability sampling gives everyone an equal chance of being surveyed

• Gallup lowered his “margin of error” to +/- 2%.

Sample Size

• Statisticians have found that 384 is the magic number for many surveys.

• By doing a probability sample of 384, you margin of error will be +/- 5%.

• To lower your margin of error, you must increase sample size:

600 = +/-4% 1067 = +/- 3%2401 = +/- 2% 9605 = +/- 1%

How do you decide upon sample size?

• For medical studies, your margin of error should ethically be in the 1-2% range – think of testing new medicines – you want to be VERY sure your results are accurate – it is literally a “matter of life or death”

• For public opinion polls – the margin of error of 3% seems to be standard. Some polls will go as high as 5%. Political opinion, though relevant, does not insist upon a small margin of error.

• How accurate do you want to be? How much money can you afford to spend? These questions will determine sample size for you. More participants = more money. Life or death = more money.

Famous Polling Organizations

• Gallup Poll - http://www.gallup.com/home.aspx

• Pew - http://people-press.org/

• Quinnipiac - http://www.quinnipiac.edu/x271.xml

• Ohio Poll - http://www.ipr.uc.edu/OhioPoll/OhioPoll.html

• NBC/WSJ - http://msnbcmedia.msn.com/i/MSNBC/Sections/NEWS/A_Politics/_Today_Stories_Teases/Correct_NBCWSJ_poll.pdf