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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

A TV station wishes to obtain information on the TV viewing habits in its market area.

The market area contains one city of population 170,000, another city of70,000, and

four towns of about 5000residents each. The station suspects that the viewing habits

may be different in larger and smaller cities and in the rural areas. Which of the

following sampling designs would yield the type of information the station requires?

a. A stratified sample from the cities and towns in the market area

b. A cluster sample using the cities and towns as clusters

c. A convenience sample from the market area

d. A simple random sample from the market area

e. An online poll that invites all people from the cities and towns in the market area to

participate.

Boys don鈥檛 cry? Two female statistics students asked a random sample of 60 high school

boys if they have ever cried during a movie. Thirty of the boys were asked directly and the

other 30 were asked anonymously by means of a 鈥渟ecret ballot.鈥� When the responses were

anonymous, 63% of the boys said 鈥淵es,鈥� whereas only 23% of the other group said 鈥淵es.鈥�

Explain why the two percentages are so different.

Tonya wanted to estimate the average amount of time that students at her school spend on Facebook each day. She gets an alphabetical roster of students in the school from the registrar鈥檚 office and numbers the students from 1 to 1137. Then Tonya uses a random number generator to pick 30 distinct labels from 1 to 1137. She surveys those 30 students about their Facebook use. Tonya鈥檚 sample is a simple random sample because

a. it was selected using a chance process.

b. it gave every individual the same chance to be selected.

c. it gave every possible sample of size 30 an equal chance to be selected.

d. it doesn鈥檛 involve strata or clusters.

e. it is guaranteed to be representative of the population.

A recent random sample of n=805adult U.S. residents found that the proportion who rated the honesty and ethical standards of nurses as high or very high is 0.85. This is 0.15higher than the proportion recorded for doctors, the next highest-ranked profession.

a. Identify the sample and the population in this setting.

b. Do you think that the proportion of all U.S. residents who would rate the honesty and ethical standards of nurses as high or very high is exactly 0.85? Explain your answer.

c. What is the benefit of increasing the sample size in this context?

SRS of engineers? A corporation employs 2000 male and 500 female engineers. A stratified random sample of 200 male and 50 female engineers gives every individual in the population the same chance to be chosen for the sample. Is it an SRS? Explain your answer.
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