Variables

In any experiment, psychologists need to identify and control variables — factors that can change or vary. Understanding variables is essential for designing valid experiments and interpreting results.

flowchart LR
    IV["Independent Variable<br/>manipulated by researcher"] -->|affects| DV["Dependent Variable<br/>measured by researcher"]
    EV["Extraneous Variables<br/>noise, time, instructions"] -.->|controlled<br/>should NOT affect| DV
    CV["Confounding Variables<br/>vary systematically with IV"] ==>|invalidates results| DV

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What is a Variable?

A variable is any factor that can change or vary in a study. In an experiment, the researcher manipulates one variable and measures its effect on another, while trying to keep all other variables constant.

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Types of Variable

Independent Variable (IV)

The independent variable is the variable that the researcher deliberately changes or manipulates to see its effect on the dependent variable.

• It is the cause in the experiment
• It is what differs between the conditions
• Example: In a study on the effect of sleep on memory, the IV might be the amount of sleep (8 hours vs 4 hours)

Dependent Variable (DV)

The dependent variable is the variable that the researcher measures to see if it has been affected by the IV.

• It is the effect in the experiment
• It is the outcome or result
• Example: In the sleep study, the DV would be the score on a memory test

Extraneous Variables

Extraneous variables are any variables other than the IV that could potentially affect the DV. If not controlled, they could provide an alternative explanation for the results.

Common extraneous variables include:

Type	Example
Participant variables	Differences between participants (age, gender, intelligence, motivation)
Situational variables	Differences in the testing environment (temperature, noise, time of day)
Experimenter variables	Differences in how the experimenter behaves (tone of voice, instructions given)

Confounding Variables

A confounding variable is an extraneous variable that has systematically varied alongside the IV, making it impossible to determine whether the IV or the confounding variable caused the change in the DV.

• A confounding variable ruins the experiment because it provides an alternative explanation for the results
• Example: If all participants in the 8-hour sleep condition were tested in the morning and all participants in the 4-hour sleep condition were tested late at night, the time of testing would be a confounding variable — you would not know whether memory differences were due to sleep or time of testing

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The Relationship Between Variables

IV (manipulated) → affects → DV (measured)

Extraneous variables (controlled) → should NOT affect → DV

Confounding variables (uncontrolled) → DO affect → DV (invalidates results)

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Controlling Extraneous Variables

Researchers use several techniques to control extraneous variables:

Technique	How It Works
Standardised procedures	Keep all aspects of the study the same for all participants (same instructions, same environment, same time limits)
Random allocation	Randomly assign participants to conditions to distribute participant variables evenly
Counterbalancing	In repeated measures, vary the order of conditions to reduce order effects
Single-blind procedure	Participants do not know which condition they are in, reducing demand characteristics
Double-blind procedure	Neither participants nor researchers know which condition participants are in, reducing both demand characteristics and experimenter bias

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Operationalisation Revisited

Both the IV and DV must be operationalised — defined in a way that can be measured and tested.

Vague	Operationalised
IV: "Type of music"	IV: "Classical music played at 60dB vs silence"
DV: "Memory"	DV: "Number of words correctly recalled from a list of 20"
IV: "Stress"	IV: "Completing a timed maths test under exam conditions vs untimed"
DV: "Anxiety"	DV: "Score on the State-Trait Anxiety Inventory (STAI)"

Exam Tip: In exam questions, you will often be given a scenario and asked to identify the IV, DV, and any extraneous or confounding variables. Always operationalise your answers — be specific about what is being changed and what is being measured.

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Key Points

• The IV is manipulated by the researcher; the DV is measured.
• Extraneous variables are factors that could affect the DV if not controlled.
• A confounding variable is an uncontrolled extraneous variable that systematically varies with the IV.
• Variables must be operationalised (defined in measurable terms).
• Control techniques include standardisation, random allocation, counterbalancing, and blinding.

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Why Variables Matter for Conclusions

The reason variables matter so much is that any conclusion drawn from a study depends on how well the variables were managed. If the IV and DV are poorly operationalised, the results will be hard to interpret. If extraneous variables are uncontrolled, confounding variables may provide alternative explanations. If confounding variables are present, the study cannot support a cause-and-effect conclusion at all.

When evaluating a study in an exam, always check: were the variables operationalised clearly? Were extraneous variables controlled? Is there any obvious confounding variable that could explain the results? Strong answers identify these issues explicitly.

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Worked Practice: Identifying Variables in Scenarios

Work through these short scenarios and identify the IV, DV and at least one possible extraneous variable.

Scenario 1: A psychologist shows 10 participants a video in a bright room and another 10 participants the same video in a dim room. She measures their reported mood on a 1-10 scale afterwards.

• IV: lighting condition (bright vs dim room)
• DV: mood rating on a 1-10 scale
• Extraneous variable: temperature of the room, time of day, individual differences in baseline mood

Scenario 2: Researchers compare the number of words recalled from a list of 30 words by participants who revised for 10 minutes versus those who revised for 30 minutes.

• IV: revision time (10 vs 30 minutes)
• DV: number of words recalled out of 30
• Extraneous variable: prior vocabulary knowledge, motivation, interruptions during revision

Scenario 3: A study compares the mean reaction time of participants tested in the morning with those tested in the evening.