An independent variable is manipulated and controlled by the researcher. A dependent variable is the variable that the researcher watches and/or measures. It is called a dependent variable because it depends upon and is affected by the independent variable. For example, a researcher may investigate the effect of sunlight on plant growth by exposing some plants to eight hours of sunlight per day and others to only four hours of sunlight per day. The plant growth rate is dependent upon the amount of sunlight, which is controlled by the researcher.