托福 托福-61 Question 3
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Diffusion Effect in Health Studies

When health education experts want to test the effectiveness of a program designed to improve a particular health condition, they often do a study with two groups of people. One group participates in the program, while the other does not: and the researchers compare the two groups to see if the program was effective in improving health. However, if the groups come into contact during the study, a diffusion effect may occur. Members of the group participating in the program may mistakenly share information about it with members of the other group. This often leads to the results of the study being useless

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Explain how the example from the lecture illustrates the concept of a diffusion effect.

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