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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

iPhonesSuppose 1000iPhones are produced at a factory today. Management would like to ensure that the phones鈥� display screens meet their quality standards before shipping them to retail stores. Because it takes about 10minutes to inspect an individual phone鈥檚 display screen, managers decide to inspect a sample of 20phones from the day鈥檚 production.

a. Explain why it would be difficult for managers to inspect an SRS of 20iPhones that are produced today.

b. An eager employee suggests that it would be easy to inspect the last 20iPhones that were produced today. Why isn鈥檛 this a good idea?

c. Another employee recommends a different sampling method: Randomly choose one of the first50 iPhones produced. Inspect that phone and every fiftieth iPhone produced afterward. (This method is known as systematic random sampling.) Explain carefully why this sampling method is not an SRS.

Cocoa and blood flow- A study of blood flow involved27healthy people aged18to72.

Each subject consumed a cocoa beverage containing900milligrams of flavanols daily for

5days. Using a finger cuff, blood flow was measured on the first and fifth days of the

study. After5days, researchers measured what they called 鈥渟ignificant improvement鈥� in

Blood flow and the function of the cells that line the blood vessels. What a flaw in the

design of this experiment makes it impossible to say if the cocoa really caused the

improved blood flow? Explain your answer.

To investigate if standing up while studying affects performance in an algebra class, a teacher assigns half of the 30students in his class to stand up while studying and assigns the other half to not stand up while studying. To determine who receives which treatment, the teacher identifies the two students who did best on the last exam and randomly assigns one to stand and one to not stand. The teacher does the same for the next two highest-scoring students and continues in this manner until each student is assigned a treatment.

Which of the following best describes this plan?

a. This is an observational study.

b. This is an experiment with blocking.

c. This is a completely randomized experiment.

d. This is a stratified random sample.

e. This is a cluster sample.

Sampling gravestones The local genealogical society in Coles County, Illinois, has compiled records on all 55,194gravestones in cemeteries in the county for the years 1825to 1985. Historians plan to use these records to learn about African Americans in Coles County鈥檚 history. They first choose an SRS of 395records to check their accuracy by visiting the actual gravestones.

a. Explain how you would use a random number generator to choose the SRS. Your description should be clear enough for a classmate to carry out your plan.

b. Use your method from part (a) to choose the first 3gravestones

Oils and inflammation The extracts of avocado and soybean oils have been shown to slow cell inflammation in test tubes. Will taking avocado and soybean unsaponifiables (called ASU) help relieve pain for subjects with joint stiffness due to arthritis? In an experiment, 345 men and women were randomly assigned to receive either

300 milligrams of ASU daily for three years or a placebo daily for three years.

Explain why it was necessary to include a control group in this experiment.
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