Chapter 4: Q. T4.2 (page 289)
You want to take a simple random sample (SRS) of of thestudents who live in
a dormitory on campus. You label the students in alphabetical order. In the
table of random digits, you read the entries
The first three students in your sample have labels.
The correct option is:
(e
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Weight? Wait what? Marcos asked a random sample of mall shoppers for their weight. Twenty-five of the shoppers were asked directly and the other were asked anonymously by means of a “secret ballot.” The mean reported weight was pounds heavier for the anonymous group. Explain why the two means are so different.
Meditation for anxiety An experiment that claimed to show that meditation lowers anxiety proceeded as follows. The experimenter interviewed the subjects and rated their level of anxiety. Then the subjects were randomly assigned to two groups. The experimenter taught one group how to meditate and they meditated daily for a month. The other group was simply told to relax more. At the end of the month, the experimenter interviewed all the subjects again and rated their anxiety level. The meditation group now had less anxiety. Psychologists said that the results were suspect because the ratings were not blind. Explain what this means and how lack of blindness could affect the reported results.
In the experiment of the preceding exercise, the subjects were randomly assigned to the
different treatments. What is the most important reason for this random assignment?
a. Random assignment eliminates the effects of other variables such as stress and body
weight.
b. Random assignment is a good way to create groups of subjects that are roughly
equivalent at the beginning of the experiment.
c. Random assignment makes it possible to make a conclusion about all men.
d. Random assignment reduces the amount of variation in blood pressure.
e. Random assignment prevents the placebo effect from ruining the results of the study.
SRS of students? At a party, there are students over age and students underage. You choose at random of those over and separately choose at random of those under to interview about their attitudes toward alcohol. You have given every student at the party the same chance to be interviewed. Is your sample an SRS? Explain your answer.
The administration at a high school with 1800 students wants to gather student opinions about parking for students on campus. It isn’t practical to contact all students.
a. Give an example of a way to choose a voluntary response sample of students. Explain how this method could lead to bias.
b. Give an example of a way to choose a convenience sample of students. Explain how this method could lead to bias.
c. Describe how to select an students from the school.
d. Explain how the method you described in part (c) avoids the biases you described in parts (a) and (b).
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