# External variables and causality

> IB Psychology · IB Psychology 2027 First Assessment
> Source: https://www.owlsprep.com/study/ib-psychology-rm-external-variables-and-causality/

The role of external variables in drawing conclusions about causality.

## Learning objectives

- The role of external variables in drawing conclusions about causality.

## Core concept

External (extraneous and confounding) variables are factors other than the independent variable that could influence the outcome. If they are not controlled, they offer rival explanations, so a difference or correlation cannot safely be read as cause and effect. Experiments try to neutralise them through control, randomisation and standardisation; non-experimental studies cannot, which is why correlation does not imply causation. Drawing a causal conclusion means first ruling out the plausible external variables.

## Key studies

IB Psychology answers must be supported by named studies. Learn these to cite as evidence:

**Stein & Friedrich (1972)** — Aggressive television increased aggression only in already-aggressive children, and prosocial television helped mainly children from lower-SES backgrounds. — *The children's prior aggression and background are external variables that moderate the effect — ignore them and you would wrongly read a simple 'TV causes behaviour' relationship.*

## Evaluation (AO3)

**Strength — the key to causal claims** — Identifying and controlling external variables is exactly what lets experiments claim cause where correlational studies cannot.

**Limitation — you cannot control everything** — In real settings countless variables operate, and controlling them creates artificiality — so some confounds always remain, and over-control costs ecological validity.

## Scope

> **note**
>
> External variables and the correlation-vs-causation limit; the method families that can or cannot control them are RM_11.

## Common pitfalls

- **Wrong:** A strong or significant relationship between two variables shows one causes the other.
  - Why it fails: A frequently penalised misconception in IB Psychology exams.
  - Correct: An uncontrolled third variable can produce the association, or moderate it. Before claiming cause, ask what external variables were controlled or ruled out — correlation alone never settles it.

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