Factors Affecting Power: Size of the Difference between Population Means (3 of 3)

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The experimenter usually has little control over the size of the effect although sometimes the experimenter can choose the levels of the independent variable to increase the size of the effect. For instance, the size of the effect may be greater when a 500 mg dose is compared to a placebo then when a 300 mg dose is compared. Naturally researchers hope that the variables they manipulate have large effects. When they do not, the power of their experiments is generally low.


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