Experimentation: In the case of experiment the experimenter studies the effect of one variable on the other by deliberately manipulating and controlling one variable. The variable which is controlled and manipulated by the experimenter is called independent variable (IV) and the variable on which the impact of independent variable is studied is known as dependent variable (DV). In a simple experiment two groups are formed. One is experimental group in which participants receive the independent variable. The other is control group in which behaviour is observed without giving the independent variable. By manipulating independent variable the experimenter is in a position to state that change induced in one variable brings change in another variable. Apart from these variables the experimenter has to also simultaneously take care of other variables which are beyond his or her control. Such variables are called relevant variables and need to be controlled as they might confound the effect of independent variable.  In experimental studies three kinds of relevant variables are taken into account. These are organismic variables, situational variables and sequential variables. Organismic variables are related to personal characteristics of the participants such as age, sex, and personality features. Situational variables are concerned with the quality of physical environment during the conduct of experiment such as temperature, humidity and noise. Sequential variables are related to the very procedure of conducting the experiment when the participant is required to be tested across several conditions. Hence exposure of the participant to varied conditions may result either in attaining proficiency due to practice effects or in developing fatigue and monotony towards experiment. 

Experimenters use the following techniques to control the unwanted effect of relevant Variables.

(i) Elimination: In this technique extraneous variables are eliminated from the experimental setting.

(ii) Making Conditions Constant: In this technique the extraneous variables which cannot be eliminated are kept constant in order to make their effect same during the entire experiment.

(iii) Matching: Through this technique the relevant variables are equated or held constant across all the conditions of experiment.