A negative control is an experiment that is run in parallel to a primary experiment with the same procedures except that the treatment is changed to something that is predicted to have no result. This is done to control for the placebo effect and to provide a baseline set of measurements for comparison to the primary experiment. A negative control is run at the same time as the primary experiment on a different population. Participants are assigned to the control group randomly and it is common for an experiment to be double-blinded such that neither participants nor experimenters know who is in the control group. The following are illustrative examples of a negative control.
No TreatmentA negative control may be a population that receive no treatment. That is to say that an independent variable is set to nothing. For example, an experiment for a snowboard wax is designed to see if the wax improves the speed of snowboarders in race conditions. The control group is given new snowboards with no wax applied. Participants in the primary experiment are given identical snowboards with the wax applied. Here the control group serves as a baseline comparison to see if the wax improves average speeds.
PlaceboA trial of a new medication uses a placebo as a negative control. The placebo is designed to look like the medication but contains a food substance that has no medical significance. This is done to control for the possibility that participants will feel healthier or perhaps be cured due to the placebo effect.
Wait List Control GroupA wait list control group is a group that receives no treatment or a placebo during an experiment. At the end of the experiment, they are given the treatment in the study or a standard treatment that is known to work. This is done for ethical reasons and to make a study more attractive to participants. For example, a trial of a new hearing aid device may assign a negative control group devices that do nothing. When the trial is over, all participants may be provided with a free device that is known to work well. This is to compensate for the stress of using a novel device that may not work well or a placebo that doesn't work at all.
This is the complete list of articles we have written about experiments.
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