So, variable is anything that varies (changes or can be changed) - for example, a characteristic, value, time, number etc. In the majority of psychological experiments you will want to see whether a change in one thing (variable 1) causes any change in another one (variable 2) - and then interpret this dependency or its absence.
1. Independent variable (IV). This is a variable which experimenter manipulates and changes to see what effect (if any!) it would have on a dependant variable.
2. Dependent variable (DV). This is the one the experimenter measures after making changes to the Independent variable.
To fully understand the concept, let us consider the following experiment as an example. Say, we want to know whether people memorise organised information better than random one. To do this, an experimenter could offer to his subjects two sets of words to memorise: one consisting of random words (e.g. sun, brick, inspiration, nail...) and another - of words united by a common theme (e.g. sun, moon, star, planet...). In this case, type of data is independent variable, controlled by the experimenter. The number of words memorised by the subjects is dependent variable which is measured by the experimenter.
As you can see, the aim of experiment determines the choice of both variables. If our goal was to see how, for example, age affects the ability to memorise words, the independent variable would be participants' age, with the dependent variable remaining the same: number of words remembered.
1. Situational variable: extraneous variables related to the environment which can affect the participant's responds - for example, temperature in the room where the experiment is being carried out.
2. Participant variable: extraneous variable which are related to individual characteristics of participants: their age, gender, mood etc.