Validity, Reliability, Bias and Causal Inference
Evaluate whether evidence measures the intended construct consistently and supports a generalisable, replicable and proportionate conclusion.
How to study A-level Psychology
For every claim, identify the mechanism, supporting evidence, method, alternative explanation, practical implication and justified conclusion.
Core concepts
Concept 1
Internal, external, ecological, temporal, population and construct validity address different relationships between method, measure and inference.
Exam cue: Name the exact form of validity or reliability at issue.
Concept 2
Reliability concerns consistency across time, observers, items or replications and can be assessed and improved in method-specific ways.
Exam cue: Explain the mechanism through which a bias changes behaviour, measurement or publication.
Concept 3
Demand characteristics, investigator effects, social desirability, sampling bias and publication practices can distort evidence without being interchangeable.
Exam cue: Match any improvement to the identified weakness and note its trade-offs.
Targeted study blocks
Multi-board knowledge
Secure the shared psychological core
Use the shared scientific quality concepts that recur in core studies, practical scenarios, data questions and extended evaluation.
Scientific reasoning
Use evidence before reaching a judgement
Build a linked evaluation: identify a threat, show its effect on the inference, propose a proportionate response and judge what conclusion remains defensible.
Risk pitfalls and guardrails
Using reliability and validity as synonyms.
Guardrail: Do not memorise a study as an isolated story or assume that one board's named research and option choices apply nationally.
Claiming realism guarantees valid causal inference.
Guardrail: Do not memorise a study as an isolated story or assume that one board's named research and option choices apply nationally.
Treating one successful replication as proof that an explanation is universally true.
Guardrail: Do not memorise a study as an isolated story or assume that one board's named research and option choices apply nationally.
Memory anchors
Internal validity
Internal validity concerns whether the observed effect can be attributed to the proposed cause.
Ecological validity
Ecological validity concerns whether findings represent behaviour in relevant everyday settings.
Test-retest reliability
Test-retest reliability compares consistency across occasions.
Inter-rater reliability
Inter-rater reliability compares agreement between independent observers or coders.
Triangulation
Triangulation examines a claim through more than one method, data source or perspective.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What does internal validity concern?
What does ecological validity ask?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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