Measurement, Reliability, Validity and Sampling
Inter-rater and test-retest reliability, construct, content, face and criterion validity, and probability and non-probability sampling approaches.
How to prepare for MRCPsych Paper B
Integrate clinical formulation, safety and current UK practice with disciplined appraisal of design, bias, estimates and applicability.
Core concepts
Concept 1
Reliability concerns consistency and measurement error, while validity concerns whether an instrument supports the intended interpretation in the population and context.
Exam cue: Name whether consistency is across raters, occasions or items before selecting a reliability statistic.
Concept 2
Probability sampling supports known selection probabilities; convenience, quota, purposive and snowball approaches answer different practical or qualitative aims with different generalisability.
Exam cue: Match face, content, criterion or construct validity evidence to the claim made for the measure.
Risk pitfalls and guardrails
Assuming a reliable measure must be valid.
Guardrail: Do not choose an option because it is merely familiar or associated; show why it best answers this lead-in.
Describing a large convenience sample as representative solely because of its size.
Guardrail: Do not choose an option because it is merely familiar or associated; show why it best answers this lead-in.
Memory anchors
Can a measure be reliable but invalid?
Yes; it may produce consistent results while measuring the wrong construct or supporting the wrong interpretation.
What is inter-rater reliability?
The consistency of ratings made by different observers assessing the same phenomenon.
What is criterion validity?
Agreement with, or prediction of, an appropriate external criterion or reference standard.
What is construct validity?
Evidence that scores behave as expected from the theory of the underlying construct.
What distinguishes probability sampling?
Each eligible unit has a known, non-zero chance of selection through a defined random process.
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
Two psychiatrists independently rate the same recorded interviews for presence or absence of catatonia. Which property is being evaluated?
The same stable patients complete an anxiety scale twice, one week apart. Which property is primarily assessed?
Answer all questions to submit.
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Move forward only after this module is stable.
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