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.
What were the experimental groups in Kaitlin’s experiment?
Interactive popup. Assistance may be required. Beans with the solution of pH of 3 added to them and beans with the solution of pH of 9 added to them.
Another part of the experiment related to the independent variable is a number of repeated trials for each level of the independent variable. In general, the more times you repeat the experiment, the more valid your results are. The possibility of obtaining misleading or inaccurate results due to experimental errors will be less. Every experiment should be carried out several times and then the results of the individual trials averaged together. The number of repeated trials used will vary depending on the experiment you are conducting. However, as a general rule, the experiment should be repeated at least three times if time allows.
In Kaitlin’s experiment she did not have repeated trials. She planted more than one bean in each cup but she should have planted the beans in at least 9 cups and watered three cups with each level of pH solution.