Science Buddies: "Ask an Expert"

Say you have an experiment with two variables. When you change one on purpose, you get a change in the other. The one you change intentionally is the "independent" variable. The one that is affected by it, or "depends" on it, is the dependent variable.

In your experiment you really have more than two factors. The weight gain of the mice is clearly the "dependent" variable. How much weight they gain "depends" on a couple of factors. One of those factors is the amount of food you give them. If you give mouse "A", quantity "a" of food every day, and give mouse "B", "b" amount of food every day, then this isn't really a variable factor. It becomes a constant factor. But because you do it over time, time is a independent variable factor.

You will end up making a chart of the weight of each mouse on the "Y" axis, and the day on the "X" axis. The time is the "independent" variable.

Now you could define the experiment differently and make the amount of food the independent variable and time a constant. You would do that by feeding different amounts of food to several mice say every day for 2 weeks. Then you could make a chart with weight gain in 2 weeks on the "Y" axis - your dependent variable, and amount of food you fed every day on the "X" axis - your independent variable.

I hope this makes sense and helps.