Below-Chance Performance
Definition
Performance on a two-alternative forced-choice task below the 50% chance level; statistically impossible through genuine impairment; meets SSI Criteria Group A for definite MND.
- Context
- Two-alternative forced-choice symptom validity testing
- Threshold
- Below 50 percent correct
- Interpretation
- Statistically impossible from genuine impairment
- Classification
- Meets SSI Criteria Group A for definite MND
Common questions
Why does scoring below chance indicate malingering rather than severe genuine impairment?+
On a forced-choice test, random guessing alone averages 50 percent correct. Even profound genuine cognitive impairment cannot push a score reliably below that baseline, since guessing sets the floor, so a below-chance score implies the subject knew the correct answer and deliberately chose the wrong one.
Does below-chance performance alone prove malingering in a legal sense?+
It is strong statistical evidence of non-credible responding on that specific test and satisfies the highest evidentiary tier in symptom validity frameworks, but a full malingered neurocognitive dysfunction determination still considers the broader clinical picture and rules out alternative explanations before a formal conclusion is reached.
Related terms
- Factitious Disorder
- Intentional production of symptoms motivated by psychological need to assume the sick role, without external incentive; distinct from malingering in motivation; not...
- M-FAST
- Miller Forensic Assessment of Symptoms Test; 25-item brief screen for feigned psychopathology; designed for jail and pretrial settings where full SIRS-2 is...
- MAL (Malingering Index)
- PAI configuration-based supplementary index developed for forensic populations to detect feigned psychopathology; used alongside NIM and clinical scales.
- Malingering
- Intentional production of false or grossly exaggerated symptoms motivated by external incentives; a DSM-5 V-code (not a mental disorder) applicable when incentive...
- Performance Validity Test (PVT)
- Any test designed to detect inadequate effort or deliberate underperformance in cognitive assessment; TOMM is the leading example for memory; embedded PVTs...
- Response Style
- The systematic approach an individual uses in reporting symptoms and behaviour during assessment; includes genuine, amplification, fabrication, defensiveness, and random responding.
- Rogers Detection of Deception Model
- Multi-source, hypothesis-testing framework for response-style assessment; requires convergent evidence from at least two data sources and explicit consideration of alternative hypotheses before...
- SIRS-2
- Structured Interview of Reported Symptoms, Second Edition; 172-item structured interview with eight primary scales for detecting feigned psychiatric symptoms; yields genuine, indeterminate,...
- Slick-Sherman-Iverson Criteria
- 1999 classification framework for Malingered Neurocognitive Dysfunction; four levels (Definite, Probable, Possible, Not MND) based on convergent evidence criteria.
- Symptom Amplification
- Exaggeration of genuine symptoms beyond their actual severity; common and does not automatically meet the malingering threshold; requires integration with all assessment...
- TOMM
- Test of Memory Malingering; 50-item forced-choice visual recognition task; Trial 2 score below 45/50 indicates performance invalidity; most widely validated memory PVT.