Comparative study: A study where the explanatory variable has two active treatments rather than an active treatment versus a control. Purpose of study is to determine which treatment works best rather than whether a treatment works. Completely randomized design: An experimental design where all individuals participating in the experiment are assigned at random to the treatments. Confounded variable: A variable whose effect on the response variable cannot be separated from the effect of the explanatory variable on the response variable. (Note: Usually confounded variables are lurking variables but only a few lurking variables are also confounded.) Confounding: A situation where the effect of one variable on the response variable cannot be separated from the effect of another variable on the response variable. Lurking variable: A variable that has an important effect on the relationship among the variables in a study but is not taken into account.
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