In section one, you learned that the independent variable should have different levels or degrees. In Kaitlin’s experiment the different levels of the independent variable were pH of 3, pH of 7, and pH of 9.
Usually one of the levels of the independent variable is the reference point or “normal” value of the variable, and the other levels will be compared with this one in order to draw conclusions from the experiment. This reference level of the independent variable, which other levels will be compared to, is called the control group for the experiment. In Kaitlin’s experiment the group of beans that was watered with the liquid that had a pH value of 7 would be the control group.
The other levels of the independent variable are referred to as the experimental group(s). Each experimental group should only have one factor different from each other, the level of the independent variable, and everything else must remain constant.