Control Condition (control group)
During many experiments, researchers often include treatment groups (the groups that are given the treatment/IV) and a control group, which is identical to the treatment group in every single way except that the control group does not get the treatment/IV. In this way, the researcher can study the effect(s) of the treatment thoroughly. For example, if I am studying the effects of 2 different pain medications of headaches, I may give people who have headaches (the treatment groups) either Tylenol or Bayer (these are the levels of the IV). I can then wait one hour and ask participants to rate the level of pain they are experiencing.
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. However, I can’t say that either are more effective than giving nothing at all. Maybe there was a placebo effect, and simply getting a pill made people believe their pain was reduced. So, I could include another group – a control group – which is treated and exposed to everything the other groups are except that they are given a placebo (maybe a sugar pill) instead of either Tylenol or Bayer. (Also see Experimental Condition).