How to experiment badly
pSubjects                              Treatment                       Measure response
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pIn a controlled environment of a laboratory (especially if human subjects are not being used), a simple design like this one, where all subjects receive the same treatment, can work well.
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q  Field experiments and experiments with human subjects are exposed to more variable conditions and deal with more variable subjects. 
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q  A simple design often yields worthless results because of confounding with lurking variables.