2. Variables: Change One Thing at a Time
GED® Science: Experimental Design & Fair Tests · preview lesson
The heart of a fair test is simple: change one thing, measure one thing, and keep the rest the same.
The independent variable is what the researcher changes. The dependent variable is what the researcher measures. Controlled variables are conditions kept the same so the comparison is fair.
Suppose you test whether fertilizer affects plant growth. The fertilizer amount is the independent variable. Plant height is the dependent variable. Water, light, soil type, pot size, and plant species should be controlled. A group with no fertilizer acts as the control group, giving you a baseline for comparison.
If you change fertilizer and water at the same time, the experiment becomes unclear. If plants grow more, which change caused it? Fair tests avoid that problem by changing only one main factor at a time.
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