Famous Quotes

• There are three kinds of lies: lies, damned lies and statistics.

– Benjamin Disraeli• Figures don’t lie; liars figure.

– Mark Twain• Statistics can be used to support anything― especially

statisticians.– Franklin P. Jones

• There are two kinds of statistics, the kind you look up and the kind you make up.

– Rex Stout• 58.6% of all statistics are made up on the spot

– Unknown

Literary Digest Poll• Literary Digest correctly predicted the

presidential election winner from 1916 to 1932.

• In 1936, they incorrectly predicted that Alf Landon would defeat FDR. – 10 Million ballots sent out– Landon chosen on 1,293,669 ballots– FDR received 972,897 ballots– Landon received 57% of returned ballots– FDR won the general election in a landslide

Where did Literary Digest go wrong?

• They had a truly huge sample size (> 2M responses), but was their sample representative of the voters as a whole?

• The Gallup poll only used 50,000 subjects and accurately predicted the winner.

WHAT THE HECK?

Rule of Large Numbers• Larger sample size will typically lend more

precision, but care must be taken to ensure that the sample is representative of the whole.

• Voluntary responses are suspect.– Why would the sample of respondents from Literary

Digest be so different than the nation as a whole? The ballots were sent to subscribers, car owners and telephone owners. They tended to be more affluent, and tended to be Republican.

– Why did Gallup’s sample give a better response?

Correlation and Causality• Just because two things are correlated does not

mean that one causes the other– 100 people were asked two questions. The first was if

they have taken pain relievers in the last week. The second was if they has a headache in the last week. 36 answered yes to question 1 and 31 answered yes to question 2.

– The percentages that answered yes to each question were very similar, so we could say that they are correlated.

– Therefore, we assume that taking pain relievers will give you a headache, right?WRONG!!!!

Reporting Results

• People often report what they think they should answer instead of the truth.– Questions such as weight, age, voting history,

charitable contributions, volunteerism, etc.• Example: 1002 eligible voters were surveyed

and 70% stated that they had voted in the presidential election.– Actual figures were closer to 61%– Is 9% difference a big deal?

Misuse of Percentages

• A start-up company held 5% of the market share of their product after year one.

• After year 2, they held a 10% market share.– In a press release, they claimed that they had a 100%

increase in market share from year to year. (5% net increase vs. 5% previous share). Is this accurate?

– What if we compared year to year the market share they didn’t have (95% vs. 90%). (95-90)÷ 95 is around 5.3% change. Is that a better way to look at it?

Misleading wording

• Should the president have the line item veto, or not? 57% yes

• Should the president have a line item veto to eliminate waste? 97% yes

• Too little money spent on welfare– 19% agreed

• Too little money is spent on assistance to the poor– 63% agreed

Order of questions

• The following questions were asked in a German poll:– Would you say that traffic contributes more or less

to air pollution than industry?– Would you say that industry contributes more or

less to air pollution than traffic?When Traffic was listed first, 45% blamed traffic and

27% blamed industry. When industry was listed first, 57% blamed industry and 24% blamed traffic.

Other problems with survey data• Non-response: Refusal to respond or unavailability. The

refusal rate is growing because of distrust of telemarketers.– People that refuse to answer often have different responses

than those that do not. What is the corresponding population that is sampled?

• Missing Data: Many sources, such as non-response or drop-out. – What can be done?

• Self-interest study: “According to a nationwide survey of 250 hiring professionals, scuffed shoes was the most common reason given for a male job-seeker’s failure to make a good first impression.” Kiwi Brands sponsored.

Homework

• Reading assignment: p. 2-17 in your statistics book. Know the terms on page 15.

• Short quiz on vocab and on