1. Samples and Surveys
population: all the members of a set sample: a part of the population convenience sample: select any members of the population who are conveniently and readily available self-selected sample: select only members of the population who volunteer for the sample systematic sample: order the population in some way, then select from it at regular intervals random sample: all members of the population are equally likely to be chosen

2. bias: a systematic error introduced by the sampling method
Samples and Surveys
bias: a systematic error introduced by the sampling method

3. Samples and Surveys
Ex. 1 For each situation, what sampling method is used? Does the sample have a bias? a) A political candidate wants to know what percent of his constituency favors Referendum A on an upcoming ballot election. His staff asks each person who comes into the candidate’s office for three days whether they support the Referendum.

4. Samples and Surveys
b) The manager of a grocery store wants to determine what percent of shoppers are using the store coupons printed in the Sunday paper. He has an employee ask every tenth shopper who passes through the store’s door for the next week if he or she intends to use a store coupon on their visit.

5. Samples and Surveys
c) A newspaper wants to find out what percent of the city population favors a wheel tax increase to raise money for more teachers. They print an article in the paper that invites readers to call the paper and express their opinion.

6. Samples and Surveys
d) A newspaper wants to find out what percent of the city population favors a property tax increase to raise money for a local park. A reporter interviews people leaving the greenway.

7. Samples and Surveys
observational study: you measure or observe members of a sample in such a way that they are not affected by the study controlled experiment: you divide the sample into two groups. You impose a treatment on one group but not on the other “control” group. Then you compare the effect on the treated group to the control group survey: you ask every member of the sample a set of questions

8. Survey questions should be clear, precise and fair. It should avoid:
Samples and Surveys
Survey questions should be clear, precise and fair. It should avoid:
combining two or more issues
using double negatives
overlapping answer choices
words that cause strong reactions (loaded question)
suggesting that you want a particular answer (leading question)

9. Samples and Surveys
Ex. 2 Is there any bias in the survey question? Explain. a) Should already high movie ticket prices be raised by fifty cents per person? b) Do you think the dress code is too strict and the punishments for violating the dress code too harsh? c) Should cell phone usage while driving be outlawed?

10. Samples and Surveys
Ex. 3 The city planning commission is considering widening a thoroughfare through the center of town to relieve traffic jams. What sampling method could you use to find the percent of city drivers who would favor a change to the thoroughfare? What survey question would you ask to avoid bias?