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Chapter 4: Q 69. (page 256)

Do placebos really work? Researchers in Japan conducted an experiment on 131 individuals who were extremely allergic to poison ivy. On one arm, each subject was rubbed with a poison ivy leaf and told the leaf was harmless. On the other arm, each subject was rubbed with a harmless leaf and told it was poison ivy. All the subjects developed a rash on the arm where the harmless leaf was rubbed. Of the

13subjects, 11 did not have any reaction to the real poison ivy leaf.

(a) What was the placebo in this experiment?

(b) Explain how the results of this study support the idea of a placebo effect.

Short Answer

Expert verified

(a) The placebo is harmless leaf.

(b) Rash developed due to under active treatment on placebo arm.

Step by step solution

01

Given Information

Research is done on 13individuals who are prone to allergy. Harmless leaf is applied to experience results one arm. Poisoned leaf on the other arm. All developed rash where leaf was rubbed. Out of them, 11did not have any reaction,

02

To determine placebo.

Placebo refers to inactive substance accessed the potency of medication. Hence, harmless leaf was placebo.

03

To explain how placebo affect results.

This is due to the fact rash is developed on arm where harmless leaf was applied (placebo). They also thought they were under active treatment (toxic leaf). It promotes placebo effect.

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Most popular questions from this chapter

Cocoa and blood flowA study conducted by Norman Hollenberg, professor of medicine at Brigham and Women’s Hospital and Harvard Medical School,

involved 27healthy people aged 18-72. Each subject consumed a cocoa beverage containing 900milligrams of flavonols (a class of flavonoids) daily

for five days. Using a finger cuff, blood flow was measured on the first and fifth days of the study. After five days, researchers measured what they called “signifi-

cant improvement” in blood flow and the function of the cells that line the blood vessels. What flaw in the design of this experiment makes it impossible to say

whether the cocoa really caused the improved blood flow? Explain.

A survey paid for by makers of disposable diapers found that 84% of the sample opposed banning disposable diapers. Here is the actual question:

It is estimated that disposable diapers account for less than 2%of the trash in today’s landfills. In contrast, beverage containers, third-class mail, and yard wastes are estimated to account for about 21% of the trash in landfills. Given this, in your opinion, would it be fair to ban disposable diapers? Explain how the wording of the question could result in bias. Be sure to specify the direction of the bias.

Online polls In June 2008, Parade magazine posed the following question: “Should drivers be banned from using all cell phones?” Readers were encouraged to vote online at parade.com. The July13,2008 issue of Parade reported the results: 2407(85%) said “Yes” and 410(15%) said “No.”

(a) What type of sample did the Parade survey obtain?

(b) Explain why this sampling method is biased. Is 85% probably higher or lower than the true percent of all adults who believe that cell phone use while

driving should be banned? Why?

Chocolate gets my heart pumping Cardiologists at Athens Medical School in Greece wanted to test whether chocolate affected blood flow in the blood vessels. The researchers recruited 17healthy young volunteers, who were each given a 3.5-ounce bar of dark chocolate, either bittersweet or fake chocolate.

On another day, the volunteers were switched. The subjects had no chocolate outside the study, and investigators didn’t know whether a subject had eaten the real or the fake chocolate. An ultrasound was taken of each volunteer’s upper arm to see the functioning of the cells in the walls of the main artery. The investigators found that blood vessel function was improved when the subjects ate bittersweet chocolate, and that there were no such changes when they ate the placebo (fake chocolate).

(a) What type of design did the investigators use in their study?

(b) Explain why the investigators chose this design instead of a completely randomized design.

(c) Why is it important to randomly assign the order of the treatments for the subjects?

Systematic random sample Sample surveys often use a systematic random sample to choose a sample of apartments in a large building or housing units in a block at the last stage of a multistage sample. Here is a description of how to choose a systematic random sample. Suppose that we must choose 4 addresses out of 100 Because 100/4=25 we can think of the list as four lists of 25 addresses. Choose 1 of the first 25 addresses at random using Table D. The sample contains this address and the addresses 25,50, and 75 places down the list from it. If the table gives 13, for example, then the systematic random sample consists of the addresses numbered 13,38,63, and 88

(a) Use Table D to choose a systematic random sample of 5 addresses from a list of 200 Enter the table at line 120

(b) Like an SRS, a systematic random sample gives all individuals the same chance to be chosen. Explain why this is true. Then explain carefully why a systematic sample is not an SRS.
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