Control variables in an experiment are the variables which are required to remain constant. An example of control variables can be found in research into the growth of micro bacteria in varying growth solutions. Control variables here are constant temperature, constant amount of light and the same amount and type of micro bacteria for each solution.

The dependent variable is the growth measured either at certain intervals or at the end of a specific period of time, another constant for all solutions and therefore another control variable.

Independent variables would be the gender of each pupil interviewed and their personal opinion. The dependent variable is the outcome of the survey.

A survey on how a new tax law is being received in various parts of a country would have the the law as the control variable; gender, age and location as independent variables and the outcome is again the dependent variable.

Research on how an insecticide may affect plants would assume control variables of pot size, soil, light, temperature and amount and type of insecticide applied. The independent variable is represented by varying plant types, the effects are the dependent variable.

Control variables play an important role in research of any kind. They provide common factors without which it would be impossible to draw valid conclusions out of the comparison of results.

- Types of variables

The dependent variable is the growth measured either at certain intervals or at the end of a specific period of time, another constant for all solutions and therefore another control variable.

- Other examples of control variables

Independent variables would be the gender of each pupil interviewed and their personal opinion. The dependent variable is the outcome of the survey.

A survey on how a new tax law is being received in various parts of a country would have the the law as the control variable; gender, age and location as independent variables and the outcome is again the dependent variable.

Research on how an insecticide may affect plants would assume control variables of pot size, soil, light, temperature and amount and type of insecticide applied. The independent variable is represented by varying plant types, the effects are the dependent variable.

Control variables play an important role in research of any kind. They provide common factors without which it would be impossible to draw valid conclusions out of the comparison of results.