In one line: A valid measure actually measures what it claims to — not something else.
Reliability asked is the measure consistent? Validity asks the harder question: is it measuring the right thing at all? Both are part of the concept of measurement.
Imagine a 'happiness' survey that mostly asks how much money people earn. It might be consistent, but it is not valid — it is measuring wealth, not happiness. A valid measure hits the target it is aiming at.
Memory hook: Reliable = same answer. Valid = right answer. You need both.
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Key idea: Validity comes in kinds: is it measuring the right concept, is the study's cause-claim safe, and does it generalise to real life?
Kinds of validity
Construct validity
Does the measure capture the actual concept? A memory test should tap memory, not reading speed or motivation.
Internal validity
In an experiment, is the effect really due to the manipulation — not a confound? Good controls protect it.
Ecological validity
Do the findings apply to real-life settings, not just the lab? A memory task with random words may not reflect everyday memory.
Right concept · Safe cause · Real life
Take a lab study claiming a drink 'boosts focus'. Construct: does the focus test really measure focus? Internal: were the two groups treated identically apart from the drink? Ecological: would the effect show up during real homework, not just a lab click-task? Each question probes a different validity.
Go further — higher-level insight: There is often a trade-off. Tightly controlling a lab study protects internal validity but can hurt ecological validity, because the situation becomes artificial. Strong evaluations point out this tension rather than treating 'more control' as always better.
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How this is tested: Validity is one of the strongest evaluation tools. For any study you can ask: is it measuring what it claims (construct), is the cause safe (internal), and does it generalise (ecological)? Name the type and explain the threat.
A study claims a five-minute breathing exercise 'improves memory', based on a lab word-recall test done straight after. Evaluate the validity of this claim.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Common mistakes: 1. Confusing validity with reliability. Consistent ≠ correct.
2. Naming validity without a threat. Say what undermines it (a confound, an artificial task).
3. Treating lab control as always best. Note the internal–ecological trade-off.