To determine what effect an independent variable (IV) or treatment may have on some measure, it is necessary to present that IV to members of a group or condition. The participants who are presented the IV are considered the experimental condition. For example, if I am studying the effects of 2 different pain medications of headaches, I may give people who have headaches either Tylenol or Bayer (the treatment groups; thus in this example there are two levels of the IV; one level is Tylenol, the other is Bayer, but both are part of the experimental condition). I can then wait one hour and ask participants to rate the level of pain they are experiencing (this would be the dependent variable or measure). If the amount of pain in one group goes down significantly more than the other, I may conclude that one medication is more effective than the other in reducing headache pain.
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