Dependent and Independent Variables – Figuring Out Which is Which

I got an email from a customer today. She was having trouble distinguishing the independent variable from the dependent. She’s doing the “Vitamin ‘C’itrus” project, in which you count the number of iodine indicator drops added to several samples of fruit juice, thus determining how much vitamin C is present in each sample.

Here’s my response: Remember, an Independent variable is what “I” change. So in this experiment, the independent variable would be the types of fruit. The dependent variable is what changes because of the independent variable (the type of fruit). And since the number of drops depends on the type of fruit, that would be the dependent variable.

Another example, from our guide:

Variables – When doing a science experiment, there are things that you, as the scientist, control to make sure your test results are dependable:
• Independent Variable – The independent variable is the thing that you change in the experiment. All the other things in your experiment should stay the same. For example, in our experiment the independent variable is the type of fertilizer. We’ll use the same kind of pot, soil, and plant. We’ll have the plants get the same amount of light and stay in the same room at the same temperature. We’ll add the same amount of water. The only thing that will change is the kind of fertilizer.
• Dependent Variable – The dependent variable is the thing that changes because of the independent variable. For us, that would be the height of the plant. The height of the plant changed because we changed the type of fertilizer.
• Control – The Control is the group in which nothing changes at all. In the fertilizer experiment, that would be the group of plants that only was given water with no fertilizer.

For more information – including step by step instructions – on this project, check out 24 Hour Science Projects.

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