psyc

hlot

ron.

org.

uk

Today’s session

You will learn about Context

The difference between extraneous and confounding variablesDetecting and correcting flaws in experiments

Studies of social and cognitive psychology and individual differences

psyc

hlot

ron.

org.

uk

The experimental method

PPs complete task under two

conditions

IV set for condition A

IV set for Condition B

DV measurements for A & B

compared

In an ideal world, the only variation within the DV measurements would be that caused by the

manipulation of the IV

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hlot

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org.

uk

The world is not idealAll the variability in the DV scores

Variability in DV caused by the IV Variability in DV caused by error

This is spread randomly across the

scores of both conditions

This affects the scores of one

condition differently from the

other

Random error

Systematic error

Systematic error

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org.

uk

All possible variables

Extraneous variables Those that may affect the DV in some way

Confounding variables Those that affect the two conditions differently

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org.

uk

• Non-confounding extraneous variables increase ‘noise’, making measurement unclear

• Confounding extraneous variables act as ‘extra IVs’ leading to mistaken conclusions about what has affected the DV (internal validity)

psyc

hlot

ron.

org.

uk

Bickman (1975)

• List some extraneous variables that might have been present in this experiment. Identify at least one that might have produced a random error and one that might have confounded the results (i.e. produced a systematic error) if left uncontrolled.