Key Idea: *Operationalise, then check the measure: is it consistent (reliable) and does it measure the right thing (valid)?*
Topic 1.4 at a glance
- Measuring behaviour — Operationalise a fuzzy idea; quantitative vs qualitative; self-report vs observation.
- Reliability — Consistency — test-retest and inter-rater agreement.
- Validity — Measuring what you claim — construct, internal, ecological.
Measure · Reliability · Validity
IB-style questionExplain[6 marks]
Explain how you would make sure a new questionnaire measuring stress is both reliable and valid.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Reliable vs valid? Reliable = same result each time; valid = the right thing (you need both).
Can a measure be reliable but not valid? Yes — consistent yet consistently wrong (a scale 5 kg heavy).
Ecological validity? Whether findings generalise to real life, not just the lab.
Reliability = consistency; validity = correctness. Name the type (test-retest, construct, ecological) for higher marks.