Official 61 Task 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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NARRATOR: Now, listen to part of a lecture on this topic in a psychology class.
MALE PROFESSOR: Let's look at an example. A researcher wanted to study ways to prevent office workers from getting stiff and tired sitting all day at their desks.
So he came up with a simple program of exercises, special stretches and things. And he wanted to know if this exercise program would keep people from getting so tired during the workday.
So he did a study. He divided the workers in an office building into two groups, group A and group B.
The researcher had group A do this new exercise program, these special exercises and stretches everyday, while group B, they were told just to work as usual.
And group A was told not to tell group B about the exercises they were doing.
The study went on for a couple of weeks. And what happened was one day some people from group A were talking about how the exercises they were doing were making them feel great that they weren't becoming so stiff and tired during the workday.
Some people from group B were sitting nearby and overheard them. So these people in group B decided to start doing the exercises, too.
So of course, the researcher wasn't able to tell how well the exercises actually worked, because people from both groups were doing them.
Question

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