Homework

• Read pages 452 - 461

• Page 467: 1 – 16, 29 – 34, 37, 38, 59

1936 Literary digest poll

• 1936 - Great Depression• Presidential election between Democrat Franklin D.

Roosevelt and Republican Alfred Landon.• Literary digest runs a poll before election

– Telephone lists, professional organizations, magazine subscriptions

– Created a list of 10,000,000 names

• From 2.4 million respondents:– Landon 57%– Roosevelt 43%

• Actual results– Landon 38%– Roosevelt 62%

Objective 8:

Developing generalizations from specific problems and examples

• Convenience Sampling: The selection off which individuals are in the sample is dictated by what is easiest for the data collector, never mind trying to get a representative sample

THE 1948 PRESIDENTIAL ELECTION(page 455)

Quota sampling is a systematic effort to force the sample to fit a certain national profile by using quotas. The sample should have so many women, so many men, so many blacks, so many whites, so many living in rural areas, so many living in urban areas, and so on. The proportions in each category in the sample should be the same as those in the electorate at large. (page 455)

1948 Presidential Election

• 1948• Presidential election between Republican Thomas Dewey

and Democrat Harry Truman.• Poll of 3250 people

– Professional interviewers given detailed quotas to meet– They go out and personally interview people until their quotas are

met• From 2.4 million respondents:

– Dewey 49.5%– Truman 44.5%– Third Party candidates 6%

• Actual results– Dewey 44.5%– Truman 49.9%

“Ain’t the way I heard it” – Harry Truman

MODERN PUBLIC OPINION POLLS (page 453)

Simple random sampling is based on the principle that any set of numbers of a given size has an equal chance of being chosen as any other set of numbers of that size.

1. Simple random sampling requires us to have a list of all the members of the population.

Difficulties of Simple random sampling

2. Simple random sampling has problems with expediency and cost.

MODERN PUBLIC OPINION POLLS

stratified sampling (page 457) - break the population into categories called strata and then randomly choose a sample from these strata. The chosen strata are then further divided into categories, called substrata, and a random sample is taken from these substrata. The selected substrata are further subdivided, a random sample is taken from them, and so on.

The critical issues are:a. Finding a sample that is representative of the population, andb. Determining how big the sample should be.

If n is the sample size and N is the population size then n/N is called the sampling rate. This is usually expressed as a percentage. A sampling rate of x% indicates that the sample is x% of the population. (page 529)

Choosing a good sample of a reasonable size is more important that the sampling rate.

• Bush's lead gets smaller in poll

• By Susan Page,

• USA TODAY WASHINGTON — President Bush leads Sen. John Kerry by 8 percentage points among likely voters, the latest USA TODAY/ CNN/Gallup Poll shows. That is a smaller advantage than the president held in mid-September but shows him maintaining a durable edge in a race that was essentially tied for months.

Results based on likely voters are based on the sub

sample of 758 survey respondents deemed most

likely to vote in the November 2004 General Election. The margin of

sampling error is ±4 percentage points.

George Gallup explained

• Whether you poll the Unites States or New York State or Baton Rouge … you need… the same number of interviews or samples. It’s no mystery really – if a cook has two pots of soup on the stove, one far larger than the other, and thoroughly stirs them both, he doesn’t have to take more spoonfuls from one than the other to sample the taste accurately.

Homework

• Read pages 446 - 461

• Page 467: 17 – 20, 25 – 27, 61, 62, 63, 67

• See if you can find an example in your life of a survey that might yield unreliable results