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Chapter 4: Q. T4.5 (page 290)

Consider an experiment to investigate the effectiveness of different insecticides in

controlling pests and their impact on the productivity of tomato plants. What is the best

reason for randomly assigning treatment levels (spraying or not spraying) to the

experimental units (farms)?

a. Random assignment eliminates the effects of other variables, like soil fertility.

b. Random assignment eliminates chance variation in the responses.

c. Random assignment allows researchers to generalize conclusions about the

effectiveness of the insecticides to all farms.

d. Random assignment will tend to average out all other uncontrolled factors such as

soil fertility so that they are not confounded with the treatment effects.

e. Random assignment helps avoid bias due to the placebo effect.

Short Answer

Expert verified

The correct option is:

d. Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects.

Step by step solution

01

Given information

We have been given four options from which we have to select the correct one.

a. Random assignment eliminates the effects of other variables, like soil fertility.

b. Random assignment eliminates chance variation in the responses.

c. Random assignment allows researchers to generalize conclusions about the

effectiveness of the insecticides to all farms.

d. Random assignment will tend to average out all other uncontrolled factors such as

soil fertility so that they are not confounded with the treatment effects.

e. Random assignment helps avoid bias due to the placebo effect.

02

Explanation

The most compelling rationale for randomization is to reduce the impact of any uncontrollable variables.Random assignment will tend to average out all other controllable variables, such as soil fertility, so that treatment effects are not confounded.

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Most popular questions from this chapter

Parking on campus The director of student life at a university wants to estimate the proportion of undergraduate students who regularly park a car on campus. Describe how to select a stratified random sample of approximately 100students. Explain your choice of strata and why stratified random sampling might be preferred in this context.

Want a snack- Can snacking on fruit rather than candy reduce later food consumption? Researchers randomly assigned12women to eat either65 calories of berries or 65calories of candy. Two hours later, all 12women were given an unlimited amount of pasta to eat. The researchers recorded the amount of pasta consumed by each subject. The women who ate the berries consumed133 fewer calories, on average. Identify the

explanatory and response variables, the experimental units, and the treatments.

High-speed Internet Laying fiber-optic cable is expensive. Cable companies want to make sure that if they extend their lines to less dense suburban or rural areas, there will be sufficient demand so the work will be cost-effective. They decide to conduct a survey to determine the proportion of households in a rural subdivision that would buy the service. They select a simple random sample of 5blocks in the subdivision and survey each family that lives on one of those blocks.

a. What is the name for this kind of sampling method?

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Weight? Wait what? Marcos asked a random sample of 50mall shoppers for their weight. Twenty-five of the shoppers were asked directly and the other 25 were asked anonymously by means of a 鈥渟ecret ballot.鈥� The mean reported weight was13 pounds heavier for the anonymous group. Explain why the two means are so different.

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Treatment 1: The accomplice was told to leave; it was explained that this was because she performed poorly.

Treatment 2: It was explained that unforeseen circumstances meant there was only enough work for one person. By 鈥渃hance,鈥� the accomplice was chosen to be laid off.

Treatment 3: Both students continued to work after the break. The subjects鈥� work performance after the break was compared with their performance before the break. Overall, subjects worked harder when told the other student鈥檚 dismissal was random.

Describe how you would randomly assign the subjects to the treatments

a. using slips of paper.

b. using technology.

c. using Table D.
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