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Chapter 4: Q 1.1. (page 211)
A farmer brings a juice company several crates of oranges each week. A company inspector looks at oranges from the top of each crate before deciding whether to buy all the oranges.
Convenience sampling.
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A sampling at the mall You have probably seen the mall interviewer, approaching people passing by with a clipboard in hand. Explain why even a large sample of mall shoppers would not provide a trustworthy estimate of the current unemployment rate.
Seat belt uses A study in El Paso, Texas, looked at seat belt use by drivers. Drivers were observed at randomly chosen convenience stores. After they left their cars, they were invited to answer questions that included questions about seat belt use. In all, 75% said they always used seat belts, yet only 61.5% were wearing seat belts when they pulled into the store parking lots.16 Explain the reason for the bias observed in responses to the survey. Do you expect bias in the same direction in most surveys about seat belt use?
Reducing unemployment Will cash bonuses speed the return to work of unemployed people? A state department of labor notes that last year of people who filed claims for unemployment insurance found a new job within weeks. As an experiment, this year the state offers to people filing unemployment claims if they find a job within weeks. The percent who do so increases to . What flaw in the design of this experiment makes it impossible to say whether the bonus really caused the increase? Explain.
Stronger players A football coach hears that a new exercise program will increase upper-body strength better than lifting weights. He is eager to test this new program in the off-season with the players on his high school team. The coach decides to let his players choose which of the two treatments they will undergo
for three weeks鈥攅xercise or weight lifting. He will use the number of push-ups a player can do at the end of the experiment as the response variable.
(a) Which principle of experimental design does the coach鈥檚 plan violate? Explain how this violation could lead to confounding.
(b) Comment on the coach鈥檚 choice of response variable.
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 bias the reported results.
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