Causality

A finding that two things tend to change together (rise or fall in step).

When one thing actually makes another happen — a stronger claim than correlation.

Two things can move together without one causing the other, so causal claims need more than a correlation.

A hidden factor that causes both correlated things (e.g. hot weather → ice cream + drownings).

When the causal direction is the opposite of what was assumed — B causes A, not A causes B.

A controlled experiment — it changes one variable while holding others constant.

It cannot rule out third variables or reverse causation, or control other factors.

More churches ↔ more crime (both driven by a bigger population — a third variable).

Causality — one of the four named concepts for Paper 2 Section B.

Spotting a real link that is worth testing properly with an experiment.

The one thing the researcher changes on purpose to see its effect.

The thing the researcher measures to see the effect of the IV.

By changing the IV while holding everything else constant, so any change in the DV is due to the IV.

A group that does not get the IV, used as a comparison.

Assigning participants to groups by chance, so the groups start out similar.

It spreads third variables evenly across groups, so they can't explain the result.

Other factors that could affect the DV; they must be controlled (kept equal).

Confidence that the IV — and nothing else — caused the change in the DV.

The experiment controls other factors and uses random allocation, ruling out third variables and reverse causation.

Causality — established through controlled experiments.

One where two things each cause the other, not just one direction.

A cycle where each thing makes the other stronger, repeating over time.

Stress and sleep — stress worsens sleep, and poor sleep worsens stress.

They show a simple, one-way 'A causes B' is often too simple for real behaviour.

Low mood leads to withdrawing, and withdrawing deepens low mood — each feeds the other.

Don't just say 'unclear direction' — explain it may run both ways in a feedback loop.

You can break any part of the loop (e.g. improve sleep) to slow the whole cycle.

Bidirectional: the two things cause each other. Third variable: a hidden factor causes both.

Causality — showing cause is not always one-way.

Not a line, a loop — the arrow points both ways.