Section_3.1_The_Design_of_Controlled_Studies[1] - The...

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The Design of Controlled Studies Controlled Studies must be carefully designed to show the influence of the treatment factor or factors on the response variable. The problem is that an apparent influence may be caused by lurking variables. Example: In countries where people’s diets contain large amounts of fat, there are high levels of intestinal cancer. Does the fat cause the cancer? We can not tell. Fat is expensive. The countries where people eat a lot of fat are richer countries with different social and economic conditions from the poorer countries where people eat less fat. Perhaps it is one or more of these other factors that causes the cancer. The other factor or factors would be lurking variables. Example: There are higher rates of leukemia among people who live near high-voltage power lines. Do the lines cause the leukemia? We don’t know, because it is impossible to separate the effects of the lines from the economic factors that cause people to live near the lines - people living near the lines tend to be poorer. And being poorer might have other consequences that can cause leukemia. The panel effect (or Hawthorne effect)
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Section_3.1_The_Design_of_Controlled_Studies[1] - The...

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