A clinician administers the PHQ-9 and obtains a score of 28 (in the severe range). She immediately records a diagnosis of major depressive disorder in the patient's chart. What is the primary limitation of this approach?
AThe PHQ-9 is not a validated instrument and should not be used in clinical settings
BA single test score, however high, underdetermines a diagnosis — diagnosis requires integrating multiple sources of data and ruling out competing explanations
CThe score should be compared to the patient's previous scores before any conclusions are drawn
DClinicians are not permitted to use self-report questionnaires as part of assessment
A PHQ-9 score provides normative comparison data but cannot by itself establish a diagnosis. Multiple conditions (hypothyroidism, bereavement, bipolar disorder) can produce high PHQ-9 scores. Diagnosis requires integrating the interview, history, rule-out of alternative explanations (differential diagnosis), and clinical judgment. Assessment data always underdetermines diagnostic conclusions — a score is a data point, not a verdict. The clinician's reasoning also risks 'premature closure': treating the first plausible diagnosis as confirmed rather than continuing to evaluate.
Question 2 Multiple Choice
A clinician uses a structured personality inventory that produces identical T-score profiles on two separate administrations six months apart. This finding tells us the instrument is:
ABoth reliable and valid — consistent results across time prove the test measures what it claims
BReliable (test-retest), but this alone tells us nothing about whether it actually measures the construct it claims to measure
CValid but not necessarily reliable — validity is a stronger criterion than reliability
DNeither reliable nor valid — personality is inherently unstable and any consistent score is a measurement artifact
Test-retest consistency is one form of reliability — it tells us the instrument produces stable, reproducible results. But reliability and validity are independent properties. A scale could consistently measure something other than its intended construct — for instance, consistently measuring social desirability rather than depression. Construct validity — whether a test actually measures the psychological construct it claims to — requires theory and convergent/discriminant evidence, not just stability. The statement 'reliable therefore valid' is the most common misunderstanding in psychometrics.
Question 3 True / False
A psychological test can be highly reliable (producing consistent results across raters and time) while still having low validity.
TTrue
FFalse
Answer: True
Reliability and validity are logically independent. A test is reliable if it produces consistent results; it is valid if it measures what it purports to measure. A scale that consistently measures neuroticism when it claims to measure depression is highly reliable but invalid for its stated purpose. Reliability is a necessary but not sufficient condition for validity — you cannot have a valid test without some reliability, but you can absolutely have a reliable test that is invalid.
Question 4 True / False
Once a DSM-5 diagnosis is established through a thorough initial assessment, it should be treated as a stable fact and used to guide most subsequent treatment decisions.
TTrue
FFalse
Answer: False
A clinical diagnosis is best understood as a working hypothesis — useful for communication, treatment selection, and research linkage, but always provisional. The Explainer explicitly calls diagnosis 'a hypothesis, not a fact' that 'should be held tentatively and updated as the clinical relationship develops.' Premature closure — failing to revise a diagnosis as new information emerges — is a recognized clinical error. Presentations change, comorbidities become apparent, initial diagnoses prove incorrect, and differential diagnoses shift. Treating a diagnosis as settled fact rather than as a hypothesis risks anchoring bias and suboptimal treatment.
Question 5 Short Answer
What is differential diagnosis, and why is it essential to clinical assessment rather than an optional step a clinician might skip if the initial presentation seems clear?
Think about your answer, then reveal below.
Model answer: Differential diagnosis is the clinician's active consideration of multiple competing explanations for the same symptom pattern — acknowledging that the observable data could be consistent with more than one diagnosis. It is essential because assessment data always underdetermines diagnostic conclusions: the same cluster of symptoms (low mood, fatigue, concentration difficulties) could reflect major depression, bipolar disorder, hypothyroidism, bereavement, or several other conditions. Skipping the differential means anchoring prematurely on the first plausible explanation and failing to gather the evidence that would distinguish alternatives. The differential diagnosis process also determines which additional assessment steps (medical workup, structured interview modules, collateral history) are warranted.
The requirement to hold multiple competing hypotheses simultaneously — and to actively seek evidence that distinguishes them — is the core scientific discipline of clinical assessment. Without it, confirmatory bias takes over: the clinician sees evidence that fits the working diagnosis and overlooks evidence that might disconfirm it. Differential diagnosis structures the assessment to be falsifiable rather than merely confirmatory.