Development and validation of the Malingering Discriminant Function Index for the MMPI-2

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Jason R Bacchiochi1, R Michael Bagby

  • 1Centre for Addiction and Mental Health, University of Toronto, Canada.

Journal of Personality Assessment
|July 22, 2006
PubMed

Insights

This study introduces a new index to detect fake-bad responses on the MMPI-2, improving accuracy when individuals know how validity scales work. The Malingering Discriminant Function Index (M-DFI) is more robust than existing scales.

Area of Science:

  • Psychological assessment
  • Forensic psychology
  • Clinical psychology

Background:

  • The Minnesota Multiphasic Personality Inventory-2 (MMPI-2) fake-bad validity scales (F, FB, FP) can be compromised by respondent knowledge.
  • Coaching on scale characteristics reduces the predictive power of traditional MMPI-2 fake-bad scales.

Purpose of the Study:

  • To develop a novel MMPI-2 fake-bad validity index resistant to respondent knowledge.
  • To create an index less vulnerable to coaching on validity scale operating characteristics.

Main Methods:

  • Discriminant function procedures were used to derive weighted Clinical and Content scales.
  • Samples included validity-scale coached undergraduate research participants feigning mental illness (n=534) and psychiatric patients (n=590).
  • The Malingering Discriminant Function Index (M-DFI) was validated on independent samples (research participants n=230, patients n=300).

Main Results:

  • The derived weighted scales reliably distinguished coached feigning participants from genuine psychiatric patients.
  • The M-DFI demonstrated less attenuation in predictive capacity compared to F, FB, and FP scales.
  • This improved performance was observed across both uncoached and coached feigning conditions.

Conclusions:

  • The Malingering Discriminant Function Index (M-DFI) offers a more robust measure for detecting feigned mental illness on the MMPI-2.
  • The M-DFI shows greater resilience against coaching regarding validity scale knowledge.
  • This index has significant implications for improving the accuracy of psychological assessments in forensic and clinical settings.

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