1. 6.6 Analyze Surveys and Samples

2. Vocabulary Survey: study of 1+ characteristics of a group
Population: entire group
Sample: part of the population
Random sample: every member of the pop. has = chance of being selected
Stratified random sample: pop. divided into groups, members are selected from each group

3. Vocabulary Systematic sample: rule used to select members of the pop.
Convenience sample: only members of the pop. who are easily accessible are selected
Self-selected sample: members volunteer
Representative sample: accurately reflects the characteristics of a pop.
Biased sample: doesn’t represent the pop.
Biased question: question that encourages a particular response

4. EXAMPLE 1
Classify a sampling method
EMPLOYEE SAFETY
The owners of a company with several factories conduct a survey to determine whether employees are informed about safety regulations. At each factory, 50 employees are chosen at random to complete the survey. Identify the population and classify the sampling method.
SOLUTION
The population is all company employees. Because the population is divided into distinct groups (individual factories), with employees chosen at random from each group, the sample is a stratified random sample.

5. GUIDED PRACTICE
1. WHAT IF? In Example 1, suppose the owners survey each employee whose last name begins with M. Classify the sampling method.
Systematic b/c rule = last name begins w/ M
ANSWER

6. EXAMPLE 2
Identify a potentially biased sample
In Example 1, suppose the owners question 50 workers chosen at random from one factory. Is the method likely to result in a biased sample?
SOLUTION
Workers at other factories may hold significantly different opinions, so the method may result in a biased sample.

7. EXAMPLE 3
Identify potentially biased questions
Tell whether the question is potentially biased. Explain your answer. If the question is potentially biased, rewrite it so that it is not.
Don’t you agree that the voting age should be lowered to 16 because many 16-year-olds are responsible and informed? a.
Do you think the city should risk an increase in pollution by allowing expansion of the Northern Industrial Park? b.

8. EXAMPLE 3
Identify potentially biased questions
SOLUTION
This question is biased because it suggests that lowering the voting age is a good thing to do. An unbiased question is “Do you think the voting age should be lowered to 16?” a.
This question is biased because it suggests that the proposed expansion will be bad for the environment. An unbiased question is “Do you think the city should allow expansion of the Northern Industrial Park?” b.

9. GUIDED PRACTICE
SOCCER
2. In a survey about Americans’ interest in soccer, the first 25 people admitted to a high school soccer game were asked, “How interested are you in the world’s most popular sport, soccer?”
Is the sampling method likely to result in a biased sample? Explain. a.
ANSWER
Yes. All people sampled were visiting a soccer game, so they may be more likely than the American population to be interested in soccer.

10. GUIDED PRACTICE
Is the question potentially biased? Explain your answer. If the question is potentially biased, rewrite it so that it is not. b.
Yes. The question suggests that soccer is popular and may encourage respondents to say they are interested in soccer.
“How interested or disinterested are you in soccer?” would be an unbiased way of asking the question.
ANSWER