A control variable in science is a variable or element that is held constant or limited in a research study to assess the relationship between multiple variables. It is not of primary interest to the studys objectives, but is controlled because it could influence the outcomes. Control variables can be controlled directly by holding them constant throughout a study, or they may be controlled indirectly through methods like randomization or statistical control.

Control variables are important because they help prevent research biases like omitted variable bias from affecting the results. In an experiment, a researcher is interested in understanding the effect of an independent variable on a dependent variable. Control variables help ensure that the results are solely caused by the experimental manipulation.

Examples of control variables include temperature, light, age, sample volume, duration of experiment, and time of year. Most experiments have multiple control variables, and they should be kept consistent throughout all experimental groups to minimize their impact on the results.