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Chapter 4: Q. 1.12 (page 294)
A linear regression was performed using the following five data points: The residual for which of the five points has The largest absolute value?
a. A
b. B
c. C
d. D
e. E
point has the largest absolute value.
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Killing weeds A biologist would like to determine which of two brands of weed killer, X or Y, is less likely to harm the plants in a garden at the university. Before spraying near the plants, the biologist decides to conduct an experiment usingindividual plants. Which of the following two plans for randomly assigning the treatments should the biologist use? Why?
Plan A: Choose thehealthiest-looking plants. Then flip a coin. If it lands heads, apply Brand X weed killer to these plants and Brand Y weed killer to the remainingplants. If it lands tails, do the opposite.
Plan B: Chooseof theplants at random. Apply Brand X weed killer to thoseplants and Brand Y weed killer to the remainingplants.
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 blocks 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?
b. Give a possible reason why the cable company chose this method.
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.
Bias in a sampling method is
a. any difference between the sample result and the truth about the population.
b. the difference between the sample result and the truth about the population due to
using chance to select a sample.
c. any difference between the sample result and the truth about the population due to
practical difficulties such as contacting the subjects selected.
d. any difference between the sample result and the truth about the population that
tends to occur in the same direction whenever you use this sampling method.
e. racism or sexism on the part of those who take the sample.
Want a snack- Can snacking on fruit rather than candy reduce later food consumption? Researchers randomly assignedwomen to eat either calories of berries or calories of candy. Two hours later, all women 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 consumed fewer calories, on average. Identify the
explanatory and response variables, the experimental units, and the treatments.
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