Variables

Psychology AS · Research methodology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

A variable is anything that can change or take different values. In an experiment the researcher changes one variable and measures another.

The independent variable (IV) is the one the researcher changes or manipulates. It forms the conditions that are compared. The dependent variable (DV) is the one the researcher measures to see whether the IV has had an effect.

Both variables must be given an operational definition. This means stating exactly how the IV is set up and how the DV is measured, so that the variable can be counted or timed and another researcher could do the same thing. "Memory" is vague; "number of words recalled out of 20" is operationalised.

Rules to remember

Independent variable (IV): the variable the researcher manipulates; it creates the conditions.
Dependent variable (DV): the variable the researcher measures.
The IV is the cause being tested; the DV is the effect.
Operational definition: a clear statement of how a variable is manipulated or measured.
An operationalised IV names the conditions, e.g. 200 mg of caffeine or no caffeine.
An operationalised DV names the measure and its unit, e.g. reaction time in milliseconds.
A DV can be measured by counts, times, scores on a test, rating scales or physiological measures such as heart rate.

Common mistake

Students mix up the two variables. Ask "what did the researcher change?" for the IV and "what did the researcher measure?" for the DV.

Worked example

Participants read a story either on paper or on a phone screen and then answer 15 questions about it. Identify the IV and the operationalised DV.

The researcher changes how the story is read, so the IV is the reading format: paper or phone screen.
The researcher measures understanding of the story, so that is the DV.
To operationalise the DV, state the measure: the number of questions answered correctly out of 15.

Answer: IV: reading on paper or on a phone screen. DV: number of correct answers out of 15.

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