Experimental method uses variables. A variable is a fact or a phenomenon within or outside the organism that evokes a response in the organism and can take on different values. The response evoked through the process is also a variable. In the context of an experiment, variables are defined as independent variables, dependent variables, and controlled variables.
The purpose of an experiment is to find out whether changes in one variable (say, X) cause changes in another variable (say, Y). Here ‘X’ is referred to as the independent variable, and ‘Y’ as the dependent variable.
Thus, independent variable is the variable that is systematically altered in an experiment. While designing an experiment, attempt is made to control the situations in such a manner that a meaningful relationship can be explored between the antecedents and consequences. Antecedents are the conditions that are present in the environment or in the organism. Those are referred to as the independent variables, when the experimenter in an experimental setting manipulates them.
In the words of Ghorpade, “An independent variable is one that can be introduced, varied, or removed by the experimenter in order to study its effect on the phenomena he studies”. When the experimenter introduces the independent variable, the response of the subject begins. When he changes the independent variable, the subject’s response changes and as he removes the independent variable, the response no longer occurs.
So independent variable is the cause of the response, in an ideal psychological experiment, there is usually one independent variable. If there are more independent variables in an experiment, complex experimental designs are used to study them.
The dependent variable in an experiment is the performance or response of the subject, it is the aspect of behaviour that is measured in an experiment. This is so called, because it depends on the independent variable.
For example, an experiment is designed to study the effect of alcohol on memory. Here, alcohol intake is the Independent variable, and the score on a memory test is the dependent variable. Precisely, dependent variable is the result of an experiment. Changes in the dependent variable occur due to manipulation of an independent variable. The dependent variable is also called the “response variable”. In a graphical presentation of the result, the independent variable is spotted along the OX axis or abscissa and dependent variable is plotted along the OY axis or ordinate.
In the context of an experiment, there may be variables other than the dependent variable, which are likely to influence the response of the subject. The experimenter does not allow those variables to influence the result. He, therefore, keeps those variables same throughout the experiment either by keeping them constant or by neutralizing them through counter balancing resigns.
For example, in studying the effect of alcohol on memory, alcohol intake is the independent variable. But the amount of materials, nature of materials, method of learning etc. are the other variables, which are likely to influence the result. These variables are called “controlled variables”.
Thus, control variables are the relevant variables in an experiment whose effects on the dependent variable are neutralized.