Validity

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

Validity is about whether a study measures what it claims to measure, so that the findings are a true picture of the behaviour. A study is valid when the change in the dependent variable is caused by the independent variable and not by something else.

Ecological validity is how well the setting and task of a study reflect real life. Artificial tasks in a laboratory often have low ecological validity.

Several things threaten validity. Subjective measures depend on the researcher's interpretation, so they may be biased; objective measures avoid this. Demand characteristics are cues that reveal the aim, so participants change their behaviour. A small or narrow sample lowers generalisability, which is how far the findings apply to other people and settings.

Rules to remember

Validity: the study tests what it claims to test.
Ecological validity: how far the findings apply to real-life settings and everyday tasks.
Demand characteristics: features of a study that let participants guess the aim and change their behaviour.
Objective measures raise validity; subjective measures can be biased by interpretation.
Generalisability: how widely the findings apply beyond the sample; low when the sample is small or unrepresentative.
Good controls and standardisation raise validity by removing uncontrolled variables.
Single-blind and double-blind designs and hiding the aim reduce demand characteristics.

Common mistake

Students mix up validity and reliability. Validity is about accuracy (measuring the right thing); reliability is about consistency (getting the same result each time).

Worked example

A study of aggression gives participants a questionnaire with the title "How aggressive are you?" printed at the top. What is the threat to validity?

The title tells participants what the study is measuring.
Knowing the aim, they may give answers that make them look less aggressive.
The scores then reflect what participants want to show, not their real aggression.

Answer: Demand characteristics, which lower the validity of the study.

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