Variable is any stimulus or event which varies or can take on different values and can be measured.
For example: Intelligence, height, weight, colour etc. are variable i.e. they can take on different values.
There are three types of variables which are as follows:
- Independent variables:
- The variable which is systematically manipulated or altered in an experiment is called Independent Variable.
- It is the cause.
- For example, to study the effect of noise on learning speed.
Here Noise is an Independent Variable which can be manipulated by having different degree of sound ranging from low to high or absence of it.
- Dependent variables:
- Dependent Variable is the variable that is measured in an experiment.
- It is the effect.
- For example, in the problem to study effect of noise on speed of learning, speed of learning is dependent variable which can be measured in terms of time taken to learn.
- Extraneous variables:
Any variable other than Independent Variable which affects the dependent variable is called Extraneous Variable or Relevant Variable.
Example: In the above problem of studying the effect of noise on speed of learning, there are many other variables which might affect the speed of learning (D.V.) like level of intelligence, emotional state of the person, individual differences in learning and difficulty level of learning material etc.
- Extraneous variables are of three types:
- Organismic variables e.g. intelligence, aptitude etc.
- Situational or environmental variables e.g. noise, temperature etc.
- Sequential variables e.g. practice effect, experimental fatigue.
The experimenter is not interested in them, so he tries to control them as far as possible.
- Random Assignment means that all the participants in an experiment must have an equal chance of being assigned to each group in the study-both in experimental and control group.
- They must have an equal chance of being exposed to each level of the independent variable.
- If it is not done, it will be difficult to say whether differences in their behavior stem from the impact of independent variable or from preexisting differences.