The document discusses sampling and bias in surveys. It defines population as the entire group being studied, and sample as a smaller subset of the population. It notes that an unbiased sample accurately represents the population, while a biased sample over or underrepresents parts of the population. It then provides examples of samples that may be biased based on who is surveyed, and gives guidance on rewriting biased survey questions in a neutral way. Finally, it presents a scenario using a random sample of 40 students out of 960 to predict how many total students favor a proposed change.

1. 10.1 samples and bias.notebook March 25, 2013
Population ­ entire group of people, animals, or objects that you want info about
Sample ­ smaller part of the population.
1. A company plans to open a new restaurant in a city. To study the preference
of people in the city, the company conducts a survey of 400 city residents.
Identify the population and the sample.

2. 10.1 samples and bias.notebook March 25, 2013
unbiased sample ­ accurately represents a population
biased sample ­ overrepresents or underrepresents part of the population
unbiased
biased

3. 10.1 samples and bias.notebook March 25, 2013
2. A town wants to know if voters favor a tax increase for a new library.
Tell whether the sample chosen is likely to be biased. Explain.
a. Survey 200 people from all town residents who have library cards.
b. Survey 20 people who come to town hall one afternoon.
c. Survey 175 people from all town residents who are registered voters.

4. 10.1 samples and bias.notebook March 25, 2013
3. Tell whether the sample chosen is likely to be biased. Explain.
a) To chose the theme of an all­school dance, you survey all of the members
of your drama class.
b)To study support for a proposed new cell phone tower, all the households
within 200 yards of the proposed site are surveyed.
c) To find out if a new Web site is easy to use, the site's designer asks five
people in the office to try it.

5. 10.1 samples and bias.notebook March 25, 2013
4. Explain why the survey question may be biased. Then rewrite the question to remove the bias.
a) Would you like to see healthy food served in our cafeteria?
b) Do you plan to vote to replace the current mayor with a more effective one?

6. 10.1 samples and bias.notebook March 25, 2013
5. You want to find out if students at your school favor a proposed change in
the school colors. Of the total of 960 students, you survey 40 who were
chosen in an unbiased way. You find that 12 of the 40 favor the change.
Predict how many students at your school favor the change.