How Many Variables Are in a Controlled Experiment?

Controlled experiments have three types of variables: dependent, independent and controlled. Independent variables, also called manipulated variables, are altered during an experiment. The resulting measurable change is the dependent, or responding, variable.

To avoid experimental error, all factors other than the dependent and independent variables are standardized and referred to as controlled variables. For example, an experiment that measures the time it takes for a candle to burn down would control variables such as wind and type of candle by conducting the test in the same windless area with the same kind of candles. The independent variable for this example is the amount of time, while the dependent variable is some other measurable aspect such as height that notes the change in the candle as it burns.