Why is it important to have a control group in an experiment?

What is the Control Group and experimental group of this experiment??

• I am doing an experiment like this:Problem: Which brand of popcorn (IV) has the highest percentage of popped kernels (DV)? Hypothesis: If we test three different types of popcorn (Orville Redenbacher, Act II, and Jolly Time) to see which has the highest percentage of popped kernels, then Orville Redenbacher will have the highest percentage because it is the most expensive so we think it will have that best quality which means that more kernels will be popped Independent Variable: the type of popcorn because the independent variable is the variable that is changed and we changed the type of popcorn. Dependent Variable: Number of popped kernels because the dependent variable is the thing that will change in your experiment based on your independent variable Experimental Group: ???? Control Group: ????

• Answer:

  In this case there is no control group. All of your points are the experimental group. If you were trying to see if these brands of popcorn (let's say they were all brand new) were better than the existing brand (let's say Safeway), then perhaps the Safeway brand would be the control and the other three would be the experimental points. In general, a control group is the group where you don't change anything, against which the experimental group is compared.