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Chapter 4: Q. R4.8 (page 288)

Does the herb St. John鈥檚 wort relieve major depression? Here is an excerpt from the report of one study of this issue: 鈥淒esign: Randomized, Double-Blind, Placebo-Controlled Clinical Trial.鈥� The study concluded that the difference in effectiveness of St. John鈥檚 wort and a placebo was not statistically significant.

a. Describe the placebo effect in this context. How did the design of this experiment account for the placebo effect?

b. Explain the purpose of the random assignment.

c. Why is a double-blind design a good idea in this setting?

d. Explain what 鈥渘ot statistically significant鈥� means in this context

Short Answer

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a. As, it gave some patients a pill that should have no effect at all but looks, tastes, and feels like the Saint-John鈥檚-wort. These people think that they are being treated, but in fact, they are not. So if they get better, this would be a case of the placebo effect.

b. The purpose of this random assignment was to create two groups of subjects that are about the same in the beginning of the experiment. As this reduces bias in the conducting of the experiment.

c. Double-blind is when neither the patient or experimenter know what treatment is given. The subject should not know which treatment they are receiving so that the researchers can measure how much placebo effect there is. But the researchers should also be blinded so that they cannot influence how they measure the results.

d. 鈥淣ot statistically significant鈥� means in this context that the difference in improvement between the two groups was not large enough to rule out potential chance variation resulting for random assignment of the variables.

Step by step solution

01

Part a. Step 1. Explanation

As, it gave some patients a pill that should have no effect at all but looks, tastes, and feels like the Saint-John鈥檚-wort. These people think that they are being treated, but in fact, they are not. So if they get better, this would be a case of the placebo effect.

02

Part b. Step 1. Explanation

The purpose of this random assignment was to create two groups of subjects that are about the same in the beginning of the experiment. As this reduces bias in the conducting of the experiment.

03

Part c. Step 1. Explanation

Double-blind is when neither the patient or experimenter know what treatment is given. The subject should not know which treatment they are receiving so that the researchers can measure how much placebo effect there is. But the researchers should also be blinded so that they cannot influence how they measure the results.

04

Part d. Step 1. Explanation

鈥淣ot statistically significant鈥� means in this context that the difference in improvement between the two groups was not large enough to rule out potential chance variation resulting for random assignment of the variables.

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Most popular questions from this chapter

Can texting make you healthier? Researchers randomly assigned 700Australian adults

to either receive usual health care or usual heath care plus automated text messages with

positive messages, such as 鈥淲alking is cheap. It can be done almost anywhere. All you

need is comfortable shoes and clothing.鈥� The group that received the text messages

showed a statistically significant increase in physical activity鈥渟tatistically significant鈥� in this context?

a. The results of this study are very important.

b. The results of this study should be generalized to all people.

c. The difference in physical activity for the two groups is greater than 0.

d. The difference in physical activity for the two groups is very large.

e. The difference in physical activity for the two groups is larger than the difference

that could be expected to happen by chance alone.

Sampling the forestTo gather data on a 1200-acre pine forest in Louisiana, the U.S. Forest Service laid a grid of 1410equally spaced circular plots over a map of the forest. A ground survey visited a sample of 10%of the plots.

a. Explain how you would use a random number generator to choose an SRS of 141plots. 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 3plots.

A maker of fabric for clothing is setting up a new line to 鈥渇inish鈥� the raw fabric. The line will use either metal rollers or natural-bristle rollers to raise the surface of the fabric; a dyeing-cycle time of either 30or40minutes; and a temperature of either 150掳Cor175掳C. Three specimens of fabric will be subjected to each treatment and scored for quality.

a. List the factors in this experiment and state how many levels each factor has.

b. If the researchers used every possible combination to form the treatments, how many

treatments were included in the experiment?

c. List two of the treatments.

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.

Precise offers People often use round prices as first offers in a negotiation. But would a more precise number suggest that the offer was more reasoned and informed? In an experiment, 238adults played the role of a person selling a used car. Each adult received one of three initial offers: \(2000, \)1865(a precise under-offer), and \(2135(a precise over-offer). After hearing the initial offer, each subject made a counter-offer. The difference in the initial offer and counter-offer was the largest in the group that received the \)2000 offer. Describe how the researchers could have randomly assigned the subjects to the treatments

a. using slips of paper.

b. using technology.

c. using Table D.
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