What is the difference between controlled variables and controls?

Answer 1

Most experiments will involve multiple samples, and there will be many factors that can change between samples, called variables. Imagine you want to test the effect of a new fertilizer on pea plant growth. You might get several pea plants (multiple samples), and give some of them fertilizer and others no fertilizer (a variable - more specifically the independent variable).

A controlled variable is a variable that you keep constant between your samples. This is usually something you know can affect your outcomes but not your independent variable. In our pea plant fertilizer experiment, one controlled variable might be water. You know water can affect plant growth, but we want to see the effect of fertilizer so we make sure all plants get equal watering.

A control is a sample that you use to help rule out variables other than the independent variable (controlled variables). The control in our pea plant experiment is the group of plants that get no fertilizer. In this case, you would use the un-fertilized pea plants as a baseline to see if your fertilizer has increased the growth of your plants.

Bottom line - a controlled variable is something you know could affect your results that you want to rule out, and a control is a sample (or set of samples) that help you do so.