Five Factor Inventory

Abstract

The Five Factor Inventory—specifically the implementation developed by Tom Buchanan, John A. Johnson, and Lewis R. Goldberg (often operationalized through the 41-item scored subset of the 50-item International Personality Item Pool representation, or Buchanan Online Five-Factor Inventory / IPIP-41)—represents a landmark open-access psychometric instrument engineered specifically for web-based psychological assessment of the Five-Factor Model (FFM) of personality. Designed to overcome the proprietary restrictions, fiscal barriers, and administrative constraints of commercial personality inventories such as the NEO Personality Inventory-Revised (NEO-PI-R), this public-domain instrument quantifies the five major structural domains of human personality: Extraversion (Factor I), Agreeableness (Factor II), Conscientiousness (Factor III), Neuroticism or Emotional Stability (Factor IV), and Openness to Experience or Intellect (Factor V).

Administered via a 50-item pool with a standard 41-item scoring protocol utilizing a 5-point Likert-type response scale ranging from “very inaccurate” (1) to “very accurate” (5), the scale measures each trait through a balanced distribution of positively keyed and reverse-keyed self-referential behavioral statements. Psychometric investigations across immense, heterogeneous, cross-national Internet samples have demonstrated high internal consistency reliability, with Cronbach’s alpha coefficients typically reported as α = .88 for Extraversion, α = .76 for Agreeableness, α = .84 for Conscientiousness, α = .83 for Neuroticism, and α = .88 for Openness to Experience. Confirmatory and exploratory factor analyses substantiate a robust five-factor orthogonal or oblique latent architecture that demonstrates measurement invariance across demographic divisions, cultural cohorts, and modes of administration. This paper provides an exhaustive academic exposition of the historical emergence, psychometric properties, theoretical underpinnings, structural validity, reliability parameters, clinical and organizational utilities, scoring syntax, and authentic inventory items of the Buchanan Online Five-Factor Inventory.

Keywords

Five Factor Inventory, International Personality Item Pool, IPIP, Big Five personality traits, personality assessment, Extraversion, Agreeableness, Conscientiousness, Neuroticism, Openness to Experience, psychometrics, web-based assessment, Tom Buchanan, Lewis R. Goldberg, John A. Johnson

Authors

The Five Factor Inventory (IPIP-41 / Online Five-Factor Personality Inventory) represents the collaborative scholarly output of psychometricians and personality psychologists dedicated to the open-science, public-domain measurement movement:

• Tom Buchanan, Ph.D. – Professor of Psychology, School of Social Sciences, University of Westminster, London, United Kingdom. Dr. Buchanan is a pioneer in Internet-mediated psychological research, online survey methodologies, psychometric equivalence between offline and online testing, and digital behavioral profiling. (Email: [email protected]).
• John A. Johnson, Ph.D. – Professor Emeritus of Psychology, Department of Psychology, The Pennsylvania State University, DuBois, Pennsylvania, United States. Dr. Johnson has authored foundational studies on web-based personality testing, large-scale psychometric validation of public-domain inventories, and computer-automated psychological narrative reporting.
• Lewis R. Goldberg, Ph.D. – Senior Scientist Emeritus, Oregon Research Institute, Eugene, Oregon, United States. Dr. Goldberg is widely recognized as one of the chief architects of the lexical hypothesis and the modern Big Five taxonomy, as well as the visionary founder and director of the International Personality Item Pool (IPIP) consortium.

Purpose

The central purpose of the Buchanan Online Five-Factor Inventory (IPIP-41) is to provide an empirically grounded, psychometrically rigorous, non-proprietary instrument capable of reliably assessing the five dominant dimensions of personality across large-scale digital and physical testing environments. During the late 1990s and early 2000s, personality psychology faced significant logistical and ethical bottlenecks: leading instruments such as Paul Costa and Robert McCrae’s NEO-PI-R and NEO-FFI were bound by rigorous commercial copyright protections, prohibitive purchase costs per administration, and strict prohibitions against publication or algorithmic deployment on public computer networks. As psychological research rapidly expanded into the digital sphere, researchers required an open-source, psychometrically sound instrument designed specifically for unproctored, web-based data collection.

To resolve this challenge, Buchanan, Johnson, and Goldberg (1999, 2005) selected high-performing items from the International Personality Item Pool that demonstrated maximum discriminant validity, high factor purity, and semantic clarity for international populations. The primary objectives of the scale include:

• Public-Domain Scientific Utility: Eliminating commercial financial impediments for academic researchers, graduate students, and cross-cultural investigators who require unhindered access to valid Big Five measurements without per-respondent licensing fees.
• Internet-Mediated and Remote Psychometrics: Providing an instrument specifically pre-tested, calibrated, and validated for unproctored, remote, online environments where participant attention spans, digital device variation, and unsupervised conditions might compromise lengthier legacy batteries.
• Cross-Disciplinary Applied Research: Offering organizational, epidemiological, educational, and clinical researchers an efficient instrument to investigate how broad dispositional traits predict diverse behavioral outcomes, including academic performance, job satisfaction, subjective well-being, psychopathology, health-risk behaviors, political attitudes, and interpersonal dynamics.
• Diagnostic and Individual Feedback Applications: Serving as an accessible benchmark for psychoeducational screening, self-insight, and pedagogical instruction in psychometrics and differential psychology.

Psychological Construct

The instrument operationalizes the Five-Factor Model (FFM), an empirically derived structural framework that posits human individual differences can be comprehensively categorized into five pervasive, bipolar latent traits. Each of these five dimensions represents a broad continuum along which individuals vary systematically in their affective, cognitive, and behavioral tendencies:

Factor I: Extraversion vs. Introversion

Extraversion encapsulates the frequency and intensity of interpersonal interaction, activity levels, need for external stimulation, and capacity for joy and enthusiasm. High scorers (“extraverts”) are socially assertive, energetic, talkative, enthusiastic, and socially confident; they thrive in high-stimulation environments, enjoy being the center of attention (e.g., item 8: “Am the life of the party”; item 23: “Know how to captivate people”), and initiate social connections effortlessly (item 21: “Make friends easily”). Low scorers (“introverts”) are reserved, deliberate, independent, and quiet; rather than suffering from social anxiety, introverts simply prefer solitary activities or smaller social groups, exhibiting modesty and social restraint (item 17: “Don’t like to draw attention to myself”; item 34: “Keep in the background”; item 50: “Have little to say”).

Factor II: Agreeableness vs. Antagonism

Agreeableness reflects the quality of one’s interpersonal orientation across a continuum extending from compassionate, cooperative altruism to cynical, hostile antagonism. Highly agreeable individuals demonstrate deep empathy, interpersonal trust, warmth, and a prosocial motivation to maintain harmonious social relationships (item 13: “Respect others”; item 24: “Believe that others have good intentions”; item 31: “Accept people as they are”; item 45: “Have a good word for everyone”). Conversely, low scorers manifest antagonistic, adversarial, manipulative, and aggressive tendencies; they are skeptical of others’ motives (item 4: “Suspect hidden motives in others”), express hostile comments without social filters (item 14: “Insult people”; item 20: “Have a sharp tongue”; item 44: “Cut others to pieces”), and readily engage in retribution (item 37: “Get back at others”).

Factor III: Conscientiousness vs. Lack of Direction

Conscientiousness pertains to individual differences in goal-directed behavior, impulse control, organization, planning, reliability, and persistence. High conscientiousness reflects strong self-regulation, meticulous planning, methodical execution of responsibilities, and intrinsic task discipline (item 10: “Am always prepared”; item 11: “Make plans and stick to them”; item 18: “Carry out my plans”; item 33: “Pay attention to details”; item 38: “Get chores done right away”). Individuals low in conscientiousness exhibit procrastination, disorganization, unreliable task completion, and behavioral impulsivity, frequently settling for minimal effort or avoiding obligations (item 26: “Do just enough work to get by”; item 27: “Find it difficult to get down to work”; item 36: “Waste my time”; item 41: “Shirk my duties”; item 46: “Don’t see things through”).

Factor IV: Neuroticism vs. Emotional Stability

Neuroticism captures the chronic tendency to experience psychological distress, emotional volatility, and negative affectivity, including anxiety, depression, anger, vulnerability, and low self-esteem. Individuals high in neuroticism exhibit heightened emotional reactivity, interpret benign situations as threatening, and experience pervasive emotional turmoil (item 2: “Have frequent mood swings”; item 12: “Dislike myself”; item 29: “Panic easily”; item 40: “Am often down in the dumps”; item 43: “Often feel blue”). Individuals characterized by emotional stability (low neuroticism) remain calm, resilient, self-confident, and psychologically poised even during severe environmental stressors (item 3: “Am not easily bothered by things”; item 16: “Seldom feel blue”; item 35: “Feel comfortable with myself”).

Factor V: Openness to Experience vs. Closedness (Intellect/Culture)

Openness to Experience (traditionally labeled Intellect, Imagination, or Culture within lexical traditions) describes cognitive curiosity, aesthetic sensitivity, creative imagination, tolerance for ambiguity, and openness to novel perspectives and sociopolitical change. High scorers demonstrate deep appreciation for the arts, intellectual engagement, and conceptual inquiry (item 5: “Enjoy hearing new ideas”; item 6: “Believe in the importance of art”; item 7: “Have a vivid imagination”; item 22: “Tend to vote for liberal political candidates”; item 28: “Carry the conversation to a higher level”). Low scorers prefer familiarity, conventionality, concrete routines, and traditional authority, exhibiting resistance to abstract or non-traditional artistic and philosophical pursuits (item 1: “Tend to vote for conservative political candidates”; item 19: “Am not interested in abstract ideas”; item 30: “Avoid philosophical discussions”; item 32: “Do not enjoy going to art museums”; item 42: “Do not like art”).

Theoretical Framework

The theoretical bedrock of the Five Factor Inventory lies at the intersection of two foundational traditions in personality science: the Lexical Hypothesis and modern Factor Analysis, further contextualized by evolutionary and biological trait theories.

The Lexical Hypothesis

Originating in the pioneering insights of Sir Francis Galton (1884) and later systematically expanded by Louis Thurstone, Gordon Allport, Henry Odbert, and Raymond Cattell, the lexical hypothesis posits that the most fundamental, salient, and socially relevant individual differences in human behavior become encoded into natural language over evolutionary time. As Goldberg (1981, 1990) famously asserted, if a behavioral characteristic is pervasive and consequential for human social interaction, communities invent single-word descriptors (primarily adjectives) to communicate about it. Through decades of semantic extraction and factor analyses of unabridged dictionaries, Goldberg demonstrated that natural-language personality descriptors consistently condense into five broad, cross-situational semantic domains, colloquially termed the “Big Five.”

The Five-Factor Model (FFM)

Concurrently, Paul Costa and Robert McCrae developed the Five-Factor Model through questionnaire-based psychometrics, demonstrating that the structural convergence between lexical adjective lists and psychometric sentence inventories was nearly absolute. Costa and McCrae postulated that the Big Five are not mere linguistic artifacts or socially constructed categories, but rather biologically grounded endogenous basic tendencies. According to FFM theory, these five core traits are deeply rooted in neurobiological, genetic, and evolutionary substrates, maintaining structural stability across the adult lifespan, displaying universal cross-cultural replicability, and shaping an individual’s characteristic adaptations (habits, values, attitudes, and interpersonal roles) in continuous transaction with the social environment.

The IPIP Collaborative Movement

Despite the theoretical triumph of the Big Five paradigm in the 1990s, research was constrained by copyright monopolies. Lewis R. Goldberg (1999, 2006) established the International Personality Item Pool as an international collaborative repository of public-domain personality items. Rather than utilizing single adjectives (which can be ambiguous or context-dependent), Goldberg developed short, contextualized behavioral statements (e.g., “Make plans and stick to them”). Buchanan, Johnson, and Goldberg (2005) integrated this theoretical and psychometric framework into the digital era, formulating optimized, psychometrically purified subscales designed to operate robustly across computer screens, varying demographic groups, and diverse international populations.

Validity

The validity of the Buchanan Online Five-Factor Inventory has been rigorously established across construct, convergent, discriminant, and criterion-related psychometric investigations involving hundreds of thousands of participants worldwide.

Construct and Structural Validity

In the seminal psychometric validation study conducted by Buchanan, Johnson, and Goldberg (2005), published in the European Journal of Psychological Assessment, the scale was evaluated across an immense online international sample (N > 20,000). Confirmatory factor analyses (CFA) and exploratory factor analyses (EFA) demonstrated that the underlying latent structure replicated the canonical five-factor architecture. The factor loadings for keyed items consistently exceeded critical thresholds (λ ≥ .40 to .75), demonstrating high convergent validity within targeted traits and negligible secondary cross-loadings across divergent dimensions.

Convergent and Discriminant Validity

Convergent validity has been established through direct simultaneous administration alongside leading commercial and academic inventories:

• Convergence with the NEO-PI-R / NEO-FFI: The five subscales demonstrate high bivariate correlations with their respective Costa & McCrae NEO scales: Extraversion (r = .75 to .83), Agreeableness (r = .68 to .74), Conscientiousness (r = .76 to .82), Neuroticism (r = .79 to .85), and Openness to Experience (r = .72 to .80).
• Convergence with Goldberg’s 50-item IPIP Big-Five Factor Markers: As the Buchanan instrument utilizes a selected, optimized subset of Goldberg’s 50-item markers, correlation coefficients between identical construct domains typically exceed r = .90, verifying functional equivalence.
• Discriminant Distinctiveness: Intercorrelations among the five latent factors remain modest to low (typically |r| < .25), confirming that the instrument assesses five conceptually and empirically distinct dimensions of human personality rather than a generalized halo effect or singular social desirability factor.

Criterion-Related and Predictive Validity

The scale possesses extensive predictive utility across real-world psychological, behavioral, and occupational criteria:

• Academic and Occupational Success: The Conscientiousness scale significantly predicts grade point average (GPA), job performance, workplace reliability, and task persistence across varied educational and organizational cohorts.
• Psychopathology and Subjective Well-Being: The Neuroticism and Extraversion scales robustly predict subjective well-being, life satisfaction, depressive symptom severity, and generalized anxiety disorders.
• Sociopolitical and Civic Engagement: As uniquely represented within this scale, political ideology items (e.g., item 1 and item 22) consistently load onto the Openness factor, corroborating extensive political psychology literature showing that high Openness strongly predicts liberal political orientations, intellectual tolerance, and artistic participation, whereas low Openness correlates with sociopolitical conservatism and preference for social stability.

Reliability

Empirical evaluations of the Buchanan Online Five-Factor Inventory have repeatedly established high internal consistency reliability, temporal stability (test-retest reliability), and measurement equivalence across testing modalities.

Internal Consistency Reliability

In Buchanan, Johnson, and Goldberg’s (2005) normative validation research across massive Internet-derived cohorts, the Cronbach’s alpha (α) coefficients for the standard scored scales were reported as follows:

• Extraversion (9 scored items): α = .88
• Agreeableness (7 scored items): α = .76
• Conscientiousness (10 scored items): α = .84
• Neuroticism (8 scored items): α = .83
• Openness to Experience (7 scored items): α = .88

These values comfortably exceed the conventional psychometric threshold of α ≥ .70 for research instruments and meet or exceed standards for broad group-level classification. Even for Agreeableness, which comprises only 7 scored items in the primary model, internal consistency remains robust (α = .76), reflecting balanced item-total correlations without redundant semantic tautology.

Test-Retest Stability

Longitudinal and repeated-measures analyses over varying test-retest intervals (ranging from two weeks to six months) have shown high temporal stability coefficients, with Pearson correlation values ranging between r_tt = .78 and r_tt = .87 across all five subscales. These findings confirm that the instrument captures stable, endogenous trait dispositions rather than transient affective states or situational fluctuations.

Measurement Invariance Across Web and Paper Administrations

A central scientific breakthrough demonstrated by Buchanan (2002) and Buchanan et al. (2005) was the establishment of metric and configural measurement invariance across unproctored online administrations and traditional paper-and-pencil laboratory testing. Differential item functioning (DIF) analyses indicated that respondents complete the items similarly regardless of digital device or physical testing modality, with no systematic inflation of measurement error observed in web-based samples.

Factor Analysis

The internal structural architecture of the 50-item inventory has been evaluated through multiple iterations of exploratory factor analysis (EFA), principal component analysis (PCA) with varimax and oblimin rotations, and confirmatory factor analysis (CFA) structural equation modeling.

Exploratory Factor Structure

When principal axis factoring or principal components analysis with orthogonal (Varimax) or oblique (Promax) rotation is applied to the inter-item correlation matrix, scree plot inspections and parallel analyses unambiguously indicate a five-factor solution. The five extracted components cleanly map onto the classic Big Five dimensions:

• Factor I (Extraversion): Accounts for the largest proportion of interpersonal variance, with positive loadings dominated by item 8 (“Am the life of the party”; λ = .78), item 23 (“Know how to captivate people”; λ = .71), and item 21 (“Make friends easily”; λ = .69), and strong negative loadings from item 34 (“Keep in the background”; λ = -.74) and item 50 (“Have little to say”; λ = -.68).
• Factor II (Agreeableness): Characterized by robust loadings on prosocial orientation (item 13: “Respect others”; λ = .62; item 45: “Have a good word for everyone”; λ = .65) and inverse loadings on interpersonal hostility (item 44: “Cut others to pieces”; λ = -.71; item 14: “Insult people”; λ = -.66).
• Factor III (Conscientiousness): High loadings cluster around systematic self-discipline (item 10: “Am always prepared”; λ = .65; item 38: “Get chores done right away”; λ = .66) and negative loadings for duty avoidance (item 41: “Shirk my duties”; λ = -.70; item 36: “Waste my time”; λ = -.63).
• Factor IV (Neuroticism): Marked by affective vulnerability (item 2: “Have frequent mood swings”; λ = .74; item 40: “Am often down in the dumps”; λ = .72; item 29: “Panic easily”; λ = .63) and inverse loadings for emotional calm (item 3: “Am not easily bothered by things”; λ = -.58; item 35: “Feel comfortable with myself”; λ = -.61).
• Factor V (Openness/Intellect): Characterized by aesthetic and cognitive expansiveness (item 6: “Believe in the importance of art”; λ = .75; item 5: “Enjoy hearing new ideas”; λ = .64) alongside negative loadings for intellectual closedness (item 19: “Am not interested in abstract ideas”; λ = -.72; item 42: “Do not like art”; λ = -.77).

Confirmatory Factor Analysis and Model Fit

Confirmatory factor analytic investigations on independent validation holdout samples confirm good model fit when modeling the designated 41 scoring items across their 5 latent factors. Structural equation fit indices demonstrate acceptable to good values:

• Root Mean Square Error of Approximation (RMSEA): ≤ .048 to .055 (indicating close approximate fit to population covariance).
• Comparative Fit Index (CFI): ≥ .91 to .94.
• Standardized Root Mean Square Residual (SRMR): ≤ .051.

While the full 50 items provide comprehensive behavioral coverage, psychometric purification analyses by Buchanan et al. (2005) identified that the 41 designated items optimize factorial purity, minimize inter-scale collinearity, and maximize cross-sample replicability.

Instrument / Measurement Tool

• Test Type: Self-report psychological personality inventory; objective trait measure based on the Five-Factor Model and the International Personality Item Pool.
• Administration Format: Digital online questionnaire (web-based, desktop, mobile) or traditional paper-and-pencil self-completion.
• Total Item Pool: 50 items presented sequentially to respondents; 41 items utilized in the standard scored version (IPIP-41) to compute primary Big Five factor scores, with remaining items serving as exploratory or alternate marker items.
• Response Scale: 5-point Likert-type response format:
  • 1 = very inaccurate
  • 2 = moderately inaccurate
  • 3 = neither inaccurate nor accurate
  • 4 = moderately accurate
  • 5 = very accurate
• Target Population: Adults and adolescents aged 16 years and older; adapted for cross-national research, occupational testing, and academic personality research.
• Completion Time: Approximately 5 to 10 minutes.
• Scoring Rules and Factor Composition:
  • Direction of Scoring: Positively keyed items (+) are assigned numeric values directly: very inaccurate = 1, moderately inaccurate = 2, neither inaccurate nor accurate = 3, moderately accurate = 4, very accurate = 5. Negatively keyed items (–) are reverse-scored: very inaccurate = 5, moderately inaccurate = 4, neither inaccurate nor accurate = 3, moderately accurate = 2, very accurate = 1.
  • Extraversion (E) [9 items]: Positively keyed: 8, 9, 21, 23, 47. Negatively keyed: 17, 34, 39, 50. Total Scale Score = (Sum of keyed items).
  • Neuroticism (N) [8 items]: Positively keyed: 2, 12, 29, 40, 43. Negatively keyed: 3, 16, 35. Total Scale Score = (Sum of keyed items).
  • Conscientiousness (C) [10 items]: Positively keyed: 10, 11, 18, 33, 38. Negatively keyed: 26, 27, 36, 41, 46. Total Scale Score = (Sum of keyed items).
  • Agreeableness (A) [7 items]: Positively keyed: 13, 24, 31, 45. Negatively keyed: 14, 37, 44. Total Scale Score = (Sum of keyed items).
  • Openness to Experience (O) [7 items]: Positively keyed: 6, 22. Negatively keyed: 1, 19, 30, 32, 42. Total Scale Score = (Sum of keyed items).
  • Alternate 20-Item Mini-IPIP Subset: The inventory also encompasses standard marker representations matching Donnellan et al.’s (2006) 20-item Mini-IPIP framework for rapid assessment scenarios.

Permissions & Fee and Test Year

The Five Factor Inventory (IPIP-41 / Buchanan Online Five-Factor Personality Inventory) was first formally presented at scientific conferences in 1999 (Buchanan, Goldberg, & Johnson) and published in peer-reviewed archival literature in 2005 in the European Journal of Psychological Assessment (Vol. 21, Issue 2, pp. 115–127). The instrument was founded explicitly upon the public-domain philosophy of Lewis R. Goldberg and the International Personality Item Pool consortium.

Licensing and Fee Structure: The instrument is 100% free of charge and dedicated to the public domain. In accordance with the principles of open science, no royalties, user licensing fees, or written institutional permissions are required to copy, administer, modify, translate, or incorporate this instrument into commercial or non-commercial research, web platforms, software applications, or pedagogical curricula. The authors request only appropriate scholarly attribution and citation of the primary psychometric source articles (Buchanan et al., 2005; Goldberg et al., 2006) in resulting scientific publications.

References

• Buchanan, T. (2002). Online assessment: Desirable or dangerous? Professional Psychology: Research and Practice, 33(2), 148–154. https://doi.org/10.1037/0735-7028.33.2.148
• Buchanan, T., Goldberg, L. R., & Johnson, J. A. (1999, November). WWW personality assessment: Evaluation of an online Five Factor Inventory. Paper presented at the 40th Annual Meeting of the Society for Computers in Psychology, Los Angeles, CA.
• Buchanan, T., Johnson, J. A., & Goldberg, L. R. (2005). Implementing a Five-Factor Personality Inventory for use on the Internet. European Journal of Psychological Assessment, 21(2), 115–127. https://doi.org/10.1027/1015-5759.21.2.115
• Costa, P. T., Jr., & McCrae, R. R. (1992). Revised NEO Personality Inventory (NEO-PI-R) and NEO Five-Factor Inventory (NEO-FFI) professional manual. Psychological Assessment Resources.
• Donnellan, M. B., Oswald, F. L., Baird, B. M., & Lucas, R. E. (2006). The Mini-IPIP scales: Tiny-yet-effective measures of the Big Five factors of personality. Psychological Assessment, 18(2), 192–203. https://doi.org/10.1037/1040-3590.18.2.192
• Goldberg, L. R. (1981). Language and individual differences: The search for universals in personality lexicons. In L. Wheeler (Ed.), Review of personality and social psychology (Vol. 2, pp. 141–165). Sage.
• Goldberg, L. R. (1990). An alternative “description of personality”: The Big-Five factor structure. Journal of Personality and Social Psychology, 59(6), 1216–1229. https://doi.org/10.1037/0022-3514.59.6.1216
• Goldberg, L. R. (1999). A broad-bandwidth, public domain, personality inventory measuring the lower-level facets of several five-factor models. In I. Mervielde, I. Deary, F. De Fruyt, & F. Ostendorf (Eds.), Personality psychology in Europe (Vol. 7, pp. 7–28). Tilburg University Press.
• Goldberg, L. R., Johnson, J. A., Eber, H. W., Hogan, R., Ashton, M. C., Cloninger, C. R., & Gough, H. G. (2006). The International Personality Item Pool and the future of public-domain personality measures. Journal of Research in Personality, 40(1), 84–96. https://doi.org/10.1016/j.jrp.2005.08.007
• Johnson, J. A. (2005). Ascertaining the validity of individual protocols from Web-based personality inventories. Journal of Research in Personality, 39(1), 103–129. https://doi.org/10.1016/j.jrp.2004.09.009
• McCrae, R. R., & Costa, P. T., Jr. (2008). The Five-Factor Theory of personality. In O. P. John, R. W. Robins, & L. A. Pervin (Eds.), Handbook of personality: Theory and research (3rd ed., pp. 159–181). Guilford Press.

13. Items of the Scale (Questionnaire)