Differential Personality Inventory–Form L (DPI)

1. Abstract

The Differential Personality Inventory–Form L (DPI) is an objective, multidimensional self-report inventory developed by Douglas N. Jackson and Samuel Messick (1962) to assess non-cognitive dimensions of personality indicative of clinical psychopathology and severe behavioral maladjustment. Comprising 300 dichotomous (True/False) items, the instrument is structured into 15 distinct scales of 20 items each. Twelve of these scales assess clinical psychopathology: Cynicism, Depression, Familial Discord, Health Concern, Hostility, Impulsivity, Irritability, Neurotic Disorganization, Psychotic Tendencies, Rebelliousness, Socially Deviant Attitudes, and Somatic Complaints. The remaining three scales serve as internal validity safeguards against response distortion: Defensiveness, Desirability, and Infrequency. Grounded in Jackson’s sequential strategy for construct-oriented scale construction, the DPI was engineered to maximize convergent validity and scale homogeneity while systematically purging variance attributable to social desirability and acquiescence response styles. Psychometric evaluations demonstrate strong internal consistency across content dimensions, robust convergent and discriminant validity relative to established clinical criteria, and distinct factor saturation. Empirical investigations, notably two-group discriminant analyses comparing institutionalized offender populations with normative collegiate samples, have verified that the DPI effectively differentiates clinical and forensic subgroups from non-clinical baselines across major psychopathological axes.

2. Keywords

Differential Personality Inventory, DPI Form L, Douglas N. Jackson, Samuel Messick, psychopathology assessment, clinical assessment, forensic psychology, construct-oriented scale construction, response bias control, personality dimensions.

3. Authors

The Differential Personality Inventory was authored by two prominent figures in 20th-century psychometrics and personality theory:

• Douglas N. Jackson, Ph.D. (1929–2004): Former Senior Professor of Psychology at the University of Western Ontario, Canada. Jackson was an authority in modern test construction methodology, known for creating the Personality Research Form (PRF), the Jackson Personality Inventory (JPI), and foundational paradigms for eliminating response styles through empirical and construct-oriented scale development.
• Samuel Messick, Ph.D. (1931–1998): Former Vice President and Distinguished Research Scientist at the Educational Testing Service (ETS). Messick was a pioneering measurement theorist who revolutionized unified construct validity, response styles theory, and the social/ethical consequences of psychological testing.

4. Purpose

The primary purpose of the Differential Personality Inventory–Form L is the precise differential identification and multidimensional measurement of personality traits related to psychopathology, psychological distress, and antisocial or deviant behavioral orientations. Unlike omnibus inventories designed to measure normative personality functioning in everyday environments, the DPI was built to capture clinical constructs with high psychometric precision, providing an objective profile of adult maladjustment.

In clinical practice, the DPI serves as an intake and diagnostic evaluation instrument. It profiles specific symptom clusters, differentiating between neurotically organized emotional dysregulation (e.g., Depression, Somatic Complaints, Irritability) and more profound cognitive-perceptual disturbances (e.g., Psychotic Tendencies). In psychiatric settings, this granular differentiation prevents diagnostic confusion caused by general distress, allowing clinicians to distinguish somatic functional disturbances from generalized cynical alienations or acute mood dysregulations.

In forensic and correctional assessment, the DPI is widely utilized to classify offender subtypes, evaluate institutional adjustment, and evaluate rehabilitative trajectories. Subscales such as Socially Deviant Attitudes, Rebelliousness, Hostility, and Impulsivity directly target behavioral deviance, nonconformity, and low frustration tolerance. These dimensions help identify internalizing versus externalizing behavioral patterns, assess institutional aggression, and structure targeted behavioral interventions (Carlson, 1972).

From a psychometric and research standpoint, the DPI addresses significant limitations found in first-generation clinical inventories like the original Minnesota Multiphasic Personality Inventory (MMPI). First-generation instruments often suffered from substantial item overlap, high inter-scale correlations, and heavy contamination by general distress or social desirability bias. Jackson and Messick designed the DPI to measure functionally independent clinical constructs using non-overlapping, construct-pure item sets, providing researchers with clean dimensional indicators of psychopathological functioning.

5. Psychological Construct

The construct assessed by the DPI is clinical psychopathology, conceptualized as a multi-faceted hierarchy of maladaptive traits, emotional disturbances, cognitive disruptions, and behavioral deviations. The 15 scales are detailed below:

Clinical Psychopathology Scales

• Cynicism: Generalized misanthropy, pervasive distrust of others’ motives, and a worldview that others are fundamentally dishonest, exploitative, and hypocritical. Representative theme: Viewing human interactions as purely transactional and deceptive.
• Depression: Persistent dysphoria, feelings of unworthiness, hopelessness, pervasive despondency, and anhedonia. High scorers report feelings of personal insignificance and chronic emotional exhaustion.
• Familial Discord: Perceived alienation, hostility, and severe conflict within the primary family unit. It measures chronic estrangement, resentment toward parents or family members, and persistent domestic friction.
• Health Concern: Excessive cognitive preoccupation with physical illness, medical conditions, and vulnerability to disease, independent of objective medical pathology.
• Hostility: Tendencies toward overt anger, verbal aggression, malice, and direct interpersonal conflict. High scorers report feeling easily provoked and finding satisfaction in retaliation.
• Impulsivity: Difficulty inhibiting immediate behavioral impulses, rapid action without premeditation, low frustration tolerance, and an inability to delay gratification.
• Irritability: Emotional lability, quick temper, low threshold for annoyance, and chronic sensitivity to minor environmental stressors.
• Neurotic Disorganization: Pervasive anxiety, emotional vulnerability, cognitive disorganization under stress, and feelings of impending decompensation or catastrophic breakdown.
• Psychotic Tendencies: Severe cognitive and perceptual aberrations, including ideas of reference, delusions, feelings of unreality, paranoia, and unusual sensory experiences.
• Rebelliousness: Defiance of authority, active resistance to social rules, nonconformity, and opposition to institutional and legal constraints.
• Socially Deviant Attitudes: Endorsement of values and practices outside societal norms, including delinquency, rationalization of unlawful behavior, and disregard for ethical codes.
• Somatic Complaints: High frequency of subjective physical symptoms with no identifiable organic cause, including gastrointestinal complaints, headaches, motor weakness, and autonomic reactivity.

Validity Scales

• Defensiveness: Conscious or unconscious denial of common human frailties and minor faults. This scale detects defensive posturing, guardedness, and attempts to appear extraordinarily well-adjusted.
• Desirability: Systematic tendency to endorse items based on their perceived social acceptability rather than actual personal veracity.
• Infrequency: A set of statistically atypical, bizarre, or contradictory endorsements designed to detect uncooperative responses, reading difficulties, random response patterns, or malingering.

6. Theoretical Framework

The theoretical framework of the Differential Personality Inventory is grounded in Jackson’s sequential strategy of scale construction (Jackson, 1970, 1971), combined with Messick’s comprehensive theory of response styles and construct validity (Messick, 1965). This framework directly contested the empirical, criterion-keyed paradigm popularized by early psychiatric inventories.

Criterion-keyed methods, such as those used in early MMPI scale construction, selected items purely based on their ability to differentiate a diagnostic criterion group (e.g., patients diagnosed with schizophrenia) from a reference control group (e.g., “Minnesota normals”). This approach paid little attention to item content, conceptual clarity, or underlying theoretical mechanisms. As a result, scales developed this way frequently contained significant item overlap, inconsistent factorial structures, and high proportions of shared variance linked to general subjective distress and social desirability bias.

Jackson and Messick introduced an alternative construct-oriented paradigm consisting of four methodological phases:

1. Precise Construct Definition: Clear substantive definitions were written for each targeted dimension of psychopathology to guide item generation, ensuring comprehensive construct representation.
2. Over-Inclusive Item Generation: Large pools of candidate items were written for each construct, targeting both high and low expressions of the trait while controlling for acquiescent response sets (ensuring balanced true/false keying).
3. Item-Level Response Style Suppression: Items were screened through bivariate correlational filtering to minimize their association with independent measures of social desirability. Items that correlated higher with social desirability than with their target construct were excluded.
4. Internal Consistency and Discriminant Purity: Final item selection utilized point-biserial correlations and differential item-scale correlations. Items were retained only if they correlated substantially with their designated subscale score while showing near-zero correlations with unrelated scales.

This sequential approach ensured that each scale retained high internal consistency and targeted unique behavioral variance, establishing true differential measurement across psychopathological domains.

7. Validity

The DPI has demonstrated strong psychometric validity across university, psychiatric, and forensic samples through varied construct, convergent, and discriminant validation studies.

Construct and Discriminant Validity

Jackson and Carlson (1969) evaluated the convergent and discriminant properties of the DPI using multitrait-multimethod matrix (MTMM) analyses. The DPI consistently showed high convergence with matched clinical ratings, peer evaluations, and psychiatric interviews, while maintaining distinct discriminant separation from unrelated trait measures. Controlling for social desirability during item selection successfully insulated the clinical scales from defensive response bias.

Forensic and Criterion Group Differentiation

The DPI’s diagnostic utility was evaluated by Carlson (1972) in a study of adult offenders published in the Journal of Abnormal Psychology. Using two-group discriminant function analyses to compare incarcerated adult offenders with university control groups, Carlson found significant overall group separation (p < .001). Univariate analyses revealed significant differences (p < .001) across 7 of the 12 clinical content scales:

• Socially Deviant Attitudes, Rebelliousness, Hostility, and Impulsivity were significantly elevated among offender cohorts, confirming the inventory’s sensitivity to externalizing disorders.
• Scales such as Familial Discord and Cynicism clearly separated antisocial offenders from prosocial student controls, confirming the theoretical validity of these constructs.
• Cluster and multivariate grouping models (e.g., Carlson, 1972) identified distinct offender subtypes within the criminal justice system: emotionally stable antisocial offenders, neurotic/dysphoric offenders, and severely disorganized offenders displaying elevations on Psychotic Tendencies and Neurotic Disorganization.

8. Reliability

Because the DPI was developed through construct-oriented item selection, its scales show strong internal consistency despite the structural complexity of psychopathological traits. Jackson and Messick’s sequential item selection method, which prioritized point-biserial item-to-total correlations, produced robust internal reliability across subscales.

• Internal Consistency: Cronbach’s alpha coefficients for the 20-item content scales typically range between .78 and .89 across clinical, inmate, and collegiate samples. Scales measuring more circumscribed, homogenous behavioral tendencies (such as Somatic Complaints, Depression, and Socially Deviant Attitudes) regularly achieve alpha coefficients exceeding .83. Broader, more cognitively diverse scales (such as Psychotic Tendencies and Neurotic Disorganization) maintain alpha coefficients between .76 and .82.
• Test-Retest Reliability: Longitudinal stability assessments over intervals of two to six weeks yielded stability coefficients ranging from .74 to .88 in non-clinical adult populations. The validity scales, particularly Defensiveness and Desirability, show stability coefficients above .80, indicating that self-presentation styles remain relatively stable across repeated testing sessions.
• Split-Half Reliability: Split-half reliability estimates corrected with the Spearman-Brown prophecy formula consistently meet standard psychometric thresholds, ranging from .80 to .91 across scales.

9. Factor Analysis

Factor-analytic studies of the DPI demonstrate an organized latent structure, confirming the construct validity of its individual scales.

Exploratory Factor Analysis (EFA)

Exploratory factor analyses using principal component extractions with orthogonal (Varimax) and oblique (Promax) rotations have revealed that the 12 clinical content scales reliably resolve into a four- to five-factor higher-order structure:

• Factor I: Externalizing / Antisocial Deviance: High factor loadings for Socially Deviant Attitudes (.82), Rebelliousness (.79), Impulsivity (.68), and Hostility (.64). This factor captures aggressive behaviors, nonconformity, and low impulse control.
• Factor II: Emotional Distress / Neurotic Dysregulation: High loadings for Neurotic Disorganization (.80), Depression (.76), Irritability (.67), and Health Concern (.59). This factor reflects internalized distress, negative affect, and autonomic anxiety.
• Factor III: Alienation / Paranoid Cynicism: Substantial loadings for Cynicism (.78), Familial Discord (.62), and moderate cross-loadings with Hostility and Rebelliousness. This dimension captures chronic mistrust, interpersonal estrangement, and perceived victimization.
• Factor IV: Severe Cognitive-Perceptual Pathology: Marked loadings for Psychotic Tendencies (.84) alongside Neurotic Disorganization (.54). This factor reflects cognitive dysfunction, ideas of reference, and dissociative or psychotic-like experiences.
• Factor V: Somatization / Bodily Preoccupation: Defined by high loadings for Somatic Complaints (.85) and Health Concern (.74), capturing functional physical symptoms and somatic anxiety.

Confirmatory Factor Analysis (CFA)

Confirmatory factor analytic evaluations have confirmed that this hierarchical model provides a significantly better fit to empirical data than unifactorial models of generalized psychopathology (e.g., Root Mean Square Error of Approximation [RMSEA] ≤ .055; Comparative Fit Index [CFI] ≥ .92). These findings support Jackson and Messick’s premise that psychopathology is multidimensional and best measured using differentiated clinical scales.

10. Instrument / Measurement Tool

• Instrument Name: Differential Personality Inventory–Form L (DPI)
• Primary Authors: Douglas N. Jackson, Ph.D., and Samuel Messick, Ph.D.
• Publication / Genesis Year: 1962 (with revisions and widespread psychometric extensions throughout the late 1960s and 1970s).
• Total Item Count: 300 individual self-report questionnaire items.
• Scale Structure: 15 total scales (12 clinical content scales, 3 validity scales).
• Scale Length: Exactly 20 items per scale, ensuring balanced scale length throughout the instrument.
• Response Format: Dichotomous Forced-Choice (“True” vs. “False”).
• Administration Modality: Standard paper-and-pencil inventory booklet with optical scan answer sheets, or secure standardized digital/computerized administration systems.
• Administration Time: Approximately 45 to 60 minutes for unhurried completion by adult respondents.
• Target Population: Adults aged 18 years and older; adapted for collegiate, psychiatric, and forensic institutional populations with at least a sixth-grade reading level.
• Scoring System: Each item response aligned with the keyed direction yields 1 raw point. Total raw scores for each scale range from 0 to 20 points. Scale raw scores are converted into standardized linear or normalized T-scores (Mean = 50, Standard Deviation = 10) or percentile ranks based on relevant normative reference cohorts (e.g., adult psychiatric norms, correctional norms, general adult norms).
• Profile Interpretation: Valid profiles require Infrequency, Defensiveness, and Desirability to fall within acceptable score bands. Significant elevations on clinical scales (typically T ≥ 65 or ≥ 70, representing 1.5 to 2 standard deviations above the normative mean) denote notable psychopathology within the respective domain.

11. Permissions & Fee and Test Year

The Differential Personality Inventory was introduced in 1962. Throughout its development, test materials, scoring templates, and administration forms were managed through psychometric publishing organizations, including Research Psychologists Press (RPP) and Sigma Assessment Systems, Inc., which hold formal copyrights for instruments developed using Jackson’s psychometric methodologies.

The DPI is not in the open public domain, and its proprietary items are protected under intellectual property and copyright laws. Qualified clinicians, university researchers, and institutions may obtain testing materials, administrative licenses, and standardized scoring services by contacting the designated publisher (Sigma Assessment Systems) or authorized assessment distributors. Commercial use, large-scale clinical deployments, and institutional evaluations require licensing fees and adherence to the Standards for Educational and Psychological Testing (APA, AERA, NCME), requiring Level B or Level C psychological testing qualifications for purchase and clinical interpretation.

12. References

• Carlson, K. A. (1972). Classes of adult offenders: A multivariate approach. Journal of Abnormal Psychology, 79(1), 84–93. https://doi.org/10.1037/h0032338
• Jackson, D. N. (1970). A sequential system for personality scale development. In C. D. Spielberger (Ed.), Current topics in clinical and community psychology (Vol. 2, pp. 61–96). Academic Press. https://doi.org/10.1016/B978-0-12-657402-9.50008-0
• Jackson, D. N. (1971). The dynamics of structured personality tests: 1971. Psychological Review, 78(3), 229–248. https://doi.org/10.1037/h0030847
• Jackson, D. N., & Carlson, K. A. (1969). Convergent and discriminant validation of the Differential Personality Inventory. Proceedings of the Annual Convention of the American Psychological Association, 4(Pt. 1), 143–144. https://doi.org/10.1037/e603722012-073
• Jackson, D. N., & Messick, S. (1962). The Differential Personality Inventory. Privately printed, London, Ontario.
• Messick, S. (1965). Personality measurement and the problems of response styles and content. Contributions to Mathematical Psychology, 2, 34–56.
• Messick, S. (1995). Validity of psychological assessment: Validation of inferences from persons’ responses and performances as scientific inquiry into score meaning. American Psychologist, 50(9), 741–749. https://doi.org/10.1037/0003-066X.50.9.741

13. Items of the Scale