Extramarital Behavioral Intentions Scale

Abstract

The Extramarital Behavioral Intentions Scale (EBIS) is a psychometric instrument developed by social psychologist Abraham P. (Bram) Buunk at the University of Nijmegen to quantify an individual’s subjective probability of engaging in non-monogamous emotional and sexual actions if provided the opportunity. Grounded in the Theory of Reasoned Action formulated by Martin Fishbein and Icek Ajzen, the instrument operationalizes behavioral intention as the direct cognitive precursor to overt behavior, conceptualizing extramarital involvement not as a binary occurrence but as a progressive behavioral continuum. The scale comprises five items spanning a spectrum of relational and physical intimacy: flirting, light petting, falling in love, sexual intercourse, and establishing a long-term sexual relationship with someone other than one’s primary committed partner. Each item is rated along a fully anchored 7-point Likert-type response scale ranging from 1 (certainly not) to 7 (certainly yes), with a neutral midpoint of 4 (uncertain), yielding a cumulative composite score between 5 and 35. Psychometric evaluations demonstrate strong internal consistency, with Cronbach’s alpha coefficients ranging from .73 to .91 across heterogeneous demographic groups, including representative community samples, university undergraduates, individuals with documented extramarital experience, and couples practicing consensual non-monogamy. Test-retest reliability across a three-month interval is established at r = .70 (p < .001). The EBIS demonstrates notable cumulative properties, satisfying the criteria of a Guttman scale with a coefficient of reproducibility of .92 and a coefficient of scalability of .78. Extensive validity studies document robust concurrent, convergent, and discriminant validity with past extramarital coitus, marital exclusivity desires, partner perceived intentions, and perceived reference group norms. This comprehensive review examines the EBIS’s structural properties, theoretical foundation, psychometric performance, and administrative applications in research and clinical contexts.

Keywords

Extramarital Behavioral Intentions Scale, EBIS, Bram Buunk, infidelity, extramarital sex, Theory of Reasoned Action, Guttman scaling, relationship exclusivity, romantic jealousy, psychometrics

Authors

The Extramarital Behavioral Intentions Scale was conceptualized, developed, and validated by Abraham P. (Bram) Buunk, PhD. During the scale’s initial formulation and psychometric testing, Dr. Buunk served as a faculty member and primary investigator within the Department of Social Psychology at the University of Nijmegen (now Radboud University Nijmegen) in the Netherlands. He subsequently held the prestigious position of Academy Professor of Evolutionary Social Psychology on behalf of the Royal Netherlands Academy of Arts and Sciences (KNAW) at the University of Groningen (Department of Psychology, Grote Kruisstraat 2/1, 9712 TS Groningen, The Netherlands; Correspondence email: [email protected]).

Dr. Buunk is internationally recognized for his pioneering contributions to social psychology, evolutionary psychology, and relationship science, having published extensively on interpersonal attraction, social comparison processes, jealousy, sexual strategies, consensual non-monogamy, and marital dynamics. His foundational work in the late 1970s and early 1980s provided the first robust, theoretically driven psychometric tools for assessing motivations, norms, and intentions surrounding extramarital relationships in both Western European and North American populations.

Purpose

The primary purpose of the Extramarital Behavioral Intentions Scale is to provide an objective, reliable, and methodologically sound measurement of an individual’s cognitive readiness and self-perceived likelihood of participating in extradyadic romantic and sexual encounters when situational barriers are removed. Prior to the construction of the EBIS, empirical investigations into marital infidelity suffered from significant methodological constraints. Most early sociological and psychological investigations relied almost exclusively on retrospective, post hoc self-reports of actual extramarital coitus. These retrospective designs created severe empirical ambiguities regarding causality: when researchers identified correlations between marital dissatisfaction, neuroticism, or communication breakdown and the occurrence of infidelity, it was impossible to discern whether dyadic distress acted as an antecedent etiology driving infidelity or emerged as an emotional and structural consequence of post-infidelity guilt, partner discovery, and marital erosion.

To overcome the limits of retrospective causality, Buunk leveraged behavioral intention modeling. By isolating behavioral intentions as an ante hoc prospective index, the EBIS permits cross-sectional and longitudinal researchers to evaluate the precise psychological, interpersonal, and normative predictors that predispose individuals to cross relationship boundaries prior to the actual occurrence of the behavior. Furthermore, because overt extramarital sexual behavior is statistically low in frequency over short longitudinal windows and heavily masked by social desirability bias, measuring intentions provides a continuous, highly sensitive psychometric variance that captures subtle inclinations toward extradyadic involvement.

In addition to empirical relationship science, the EBIS provides diagnostic utility in clinical psychology, marital therapy, and sex therapy. Therapists working with couples navigating trust erosion, open relationship negotiations, or boundary definitions utilize the scale’s continuum to map cognitive discrepancies between partners. By examining disparities in how partners endorse emotional versus strictly sexual intentions, clinicians can facilitate transparent dialogues regarding implicit relational contracts, anticipated vulnerabilities, and relational commitment.

Psychological Construct

The construct measured by the EBIS is extramarital behavioral intention, conceptualized as a continuous, multidimensional continuum of subjective probabilities regarding romantic and sexual involvement outside one’s primary partnership. Historically, infidelity had been operationalized in a reductionist, dichotomous fashion: individuals were categorized merely as having engaged in extramarital sexual intercourse or having remained completely faithful. Buunk argued that this operationalization overlooked the nuanced psychological landscape of romantic involvement, which transitions through progressive stages of intimacy, emotional attachment, and physical expression.

The EBIS captures this continuum across five core behavioral manifestations:

• Flirting: Low-threshold social-sexual signaling, verbal banter, and reciprocal expressions of attraction outside the dyad. This represents the entry-level behavior along the non-monogamous continuum, frequently functioning as an exploratory mechanism to gauge mutual interest without necessarily committing to physical boundary violations.
• Falling in Love: Deep affective investment and emotional attachment directed toward an extradyadic individual. This dimension taps into emotional infidelity, reflecting a willingness to form romantic attachments that may threaten the primary partner’s emotional exclusivity independent of or alongside physical sexual behavior.
• Light Petting: Non-coital, sensual physical contact, including intimate kissing, fondling, and foreplay. This represents an intermediate physical threshold where non-verbal, bodily boundaries are crossed, demonstrating tactile physical intimacy without progression to intercourse.
• Sexual Intercourse: Full genital, coital sexual engagement. This behavior constitutes the traditional physical benchmark of infidelity in marital law and social science literature, representing a profound violation of conventional monogamous norms.
• Long-Term Sexual Relationship: Sustained, recurrent non-monogamous involvement combining ongoing sexual intimacy with temporal endurance. This represents the most intensive end of the continuum, signifying not merely an isolated opportunistic encounter, but the maintenance of a secondary parallel relationship or affair.

Crucially, the construct isolates the subjective probability of these behaviors conditional on situational opportunity (“if the opportunity were to present itself”). This conditional phrasing eliminates confounding external barriers—such as lack of attractive alternatives, geographical isolation, or intense monitoring by the partner—thereby assessing the respondent’s underlying psychological propensity rather than incidental opportunity constraints.

Theoretical Framework

The Extramarital Behavioral Intentions Scale is situated within two foundational psychological frameworks: the Theory of Reasoned Action (TRA) formulated by Martin Fishbein and Icek Ajzen (1975) and Guttman Scaling Theory (Louis Guttman, 1944).

The Fishbein-Ajzen Paradigm

Under the Fishbein-Ajzen paradigm, human social action is governed by a causal sequence running from personal beliefs and evaluations to behavioral intentions, which in turn function as the immediate structural determinants of overt action. An individual’s intention is defined as the subjective probability that they will perform a specified behavior under designated circumstances:

B ≈ I = (A_B)w₁ + (SN)w₂

Where B represents manifest behavior, I is the behavioral intention, A_B is the personal attitude toward performing the behavior, SN represents subjective norms (perceived social expectations from salient reference groups), and w₁, w₂ are empirically derived regression weights. Buunk recognized that while predicting actual marital coitus directly from generalized attitudes yields weak empirical associations due to situational variability, measuring the specific conditional intention provides an exceptionally accurate proxy for future non-monogamous behavior. The EBIS operationalizes this intention component directly, providing the missing link between marital attitudes, normative pressures, and eventual behavior.

Guttman’s Cumulative Model

Simultaneously, the scale is constructed upon Guttman’s cumulative dimensional model. Guttman scaling posits that items measuring a single underlying unidimensional construct can be ranked hierarchically such that endorsement of an item representing a high threshold of difficulty or intensity implies the automatic endorsement of all preceding lower-threshold items. In the context of extramarital involvement, Buunk hypothesized that extradyadic intimacy develops sequentially: individuals rarely engage in a long-term sexual affair without first demonstrating a willingness to engage in flirting, emotional attachment, and petting. By confirming that extramarital intentions conform to a Guttman progression, the EBIS validated that infidelity is a progressive, staged continuum rather than an erratic, discrete event.

Validity

The Extramarital Behavioral Intentions Scale has been subjected to extensive psychometric evaluations across multiple independent cohorts, confirming exceptional concurrent, construct, convergent, and discriminant validity.

Concurrent and Criterion Validity

In a large, representative demographic sample of the Dutch general population (N = 250), Buunk established significant concurrent validity between EBIS composite scores and self-reported extramarital sexual behavior during the preceding 12 months, yielding a strong correlation of r(250) = .74, p < .001. Individuals reporting higher behavioral intentions consistently reported higher frequencies and more varied forms of extradyadic encounters.

Known-Groups Discriminant Validity

The scale possesses remarkable power to discriminate between distinct social groups differing in socio-sexual philosophy and lifestyle contracts:

• Couples practicing consensual non-monogamy in sexually open marriages scored significantly higher on the EBIS than individuals drawn from the general community population, t(348) = 22.46, p < .001.
• The open marriage cohort similarly demonstrated dramatically elevated intention scores when compared to a normative sample of unmarried undergraduate university students, t(478) = 15.16, p < .001.
• The scale demonstrated clear differentiation between individuals whose primary reference peer networks endorsed extramarital permissiveness versus those whose peers enforced strict monogamous compliance, establishing that perceived social reference norms directly align with EBIS scores.

Construct and Convergent Validity

Construct validity has been verified through robust associations with established relational and attitudinal inventories:

• Desire for Relational Exclusivity: Scores on the EBIS correlated strongly and negatively with validated measures assessing the desire for an exclusive dyadic relationship, r(250) = -.54, p < .001.
• Moral Disapproval: The scale exhibited strong inverse associations with standardized inventories measuring moral condemnation of extramarital sex, r(250) = -.65, p < .001, demonstrating that low intentions reflect internal moral prohibitions.
• Relational Variety and Extradyadic Intimacy: Significant positive correlations emerged with inventories measuring individual needs for relational variety, personal autonomy, and extradyadic emotional intimacy.
• Anticipated Sexual Jealousy: Across three independent samples, Buunk documented robust negative correlations between EBIS scores and measures of anticipated sexual jealousy, indicating that individuals who tolerate non-monogamous intentions in themselves experience significantly less jealousy regarding partner non-monogamy.
• Psychosexual Stimulation: In an empirical sample of individuals with verified histories of extramarital relationships, the EBIS correlated positively with Frenken’s (1976) Psychosexual Stimulation Scale, r(250) = .21, p < .001, verifying that higher intentions correspond to an active openness to sexual fantasy and perceptual stimulation rather than cognitive suppression.
• Spousal Perceptual Concordance: In a dyadic validation study within sexually open relationships, female participants’ EBIS scores correlated highly with their husbands’ independent perceptions of their wives’ intentions, r(50) = .53, p < .001. The corresponding spousal concordance for male participants was likewise statistically significant, r(50) = .42, p < .001, confirming substantial observational validity across intimate partners.

Reliability

The EBIS demonstrates robust psychometric reliability across diverse demographic strata, relationship structures, and temporal intervals.

Internal Consistency

Internal consistency estimates have been evaluated across four diverse developmental and relational cohorts:

• General Dutch Community Sample: In a heterogeneous normative sample characterized by widely varying levels of sexual permissiveness, the scale demonstrated excellent internal consistency, yielding a Cronbach’s alpha of α = .91 (Buunk, 1980a).
• Undergraduate Student Sample: In a sample of young adult university undergraduates, the scale demonstrated high homogeneity, yielding an alpha coefficient of α = .87.
• Consensual Non-Monogamy Sample: Among individuals in self-declared sexually open marriages, the scale maintained solid reliability with α = .75 (Buunk, 1980b).
• Extramarital Experienced Sample: In a clinical-empirical sample composed exclusively of individuals with established histories of extramarital involvement, the scale achieved an internal consistency of α = .73 (Buunk, 1982).

Temporal Stability (Test-Retest Reliability)

Stability across time was investigated in a longitudinal evaluation involving couples in sexually open marriages over a three-month test-retest window. The evaluation yielded a test-retest correlation coefficient of r(100) = .70, p < .001. This coefficient confirms that while behavioral intentions display responsiveness to significant contextual shifts, the psychological readiness captured by the scale functions as a stable cognitive orientation over medium-term horizons.

Factor Analysis and Scalability

The structural cohesion and dimensional organization of the EBIS have been evaluated using both parametric factor analysis and non-parametric cumulative scaling methods.

Dimensional Unidimensionality

Exploratory factor analyses across general population datasets confirm that the five items load onto a single dominant latent factor accounting for substantial explained variance. Factor loadings for individual items consistently exceed .65, demonstrating that despite the distinction between affective involvement (“falling in love”) and physical intimacy (“sexual intercourse”), these behaviors coalesce around an overarching latent orientation toward relationship non-exclusivity.

Guttman Scalogram Analysis

Because the scale was explicitly engineered to assess a hierarchical continuum of intimacy, Buunk submitted the five items to Guttman scalogram analysis (Green’s technique). The empirical findings satisfied all classic Guttman requirements for cumulative unidimensionality:

• Coefficient of Reproducibility (CR): The EBIS achieved a CR of .92, surpassing the accepted psychometric benchmark of .90, which confirms that an individual’s total score allows accurate prediction of their exact pattern of item endorsement.
• Coefficient of Scalability (CS): The scale achieved a CS of .78, substantially exceeding the conventional psychometric threshold of .60, establishing that the observed order of items does not arise from marginal frequency artifacts.

The empirically verified Guttman hierarchy of behavioral progression, ordered from lowest threshold (most readily endorsed) to highest threshold (most restrictive), is:

1. Flirting (Lowest threshold; widespread endorsement)
2. Falling in love (Emotional attraction threshold)
3. Light petting (Initial physical intimacy threshold)
4. Sexual intercourse (Coital boundary threshold)
5. A long-term sexual relationship (Highest threshold; enduring parallel partnership)

This verified order demonstrates an intriguing psychological insight: within normative populations, falling in love is positioned as an intermediate threshold alongside or slightly preceding physical contact, while establishing an ongoing, long-term affair represents the most demanding cognitive threshold of non-monogamy.

Instrument / Measurement Tool

• Instrument Name: Extramarital Behavioral Intentions Scale (EBIS)
• Developer: Abraham P. (Bram) Buunk, PhD
• Primary Construct: Subjective probability of engaging in extramarital sexual and emotional involvement
• Number of Items: 5 items
• Administration Format: Self-administered paper-and-pencil questionnaire, computerized survey, or structured clinical interview
• Administration Time: Approximately 1 to 2 minutes
• Target Population: Adults (18+ years) involved in committed, married, or cohabiting romantic relationships
• Response Format: 7-point fully anchored Likert scale:
  • 1 = Certainly not
  • 2 = Probably not
  • 3 = Maybe not
  • 4 = Uncertain
  • 5 = Maybe yes
  • 6 = Probably yes
  • 7 = Certainly yes
• Scoring Procedure:
  • Sum the numerical responses across all five items.
  • Reverse scoring: None (all items are keyed in a positive direction).
  • Possible score range: 5 to 35.
  • Interpretation: Higher cumulative scores reflect an elevated intention and psychological readiness to engage in extradyadic behaviors if the opportunity presents itself.

Permissions & Fee and Test Year

The Extramarital Behavioral Intentions Scale was first developed and empirically published in 1980 as part of Bram Buunk’s extensive investigations into marital dynamics, sexual open marriages, and non-monogamous lifestyle patterns in the Netherlands (Buunk, 1980a, 1980b). Additional validation studies and cross-group psychometric analyses were published in 1981 and 1982.

The scale was developed as an open scientific research instrument intended for academic, non-commercial psychological and sociological research. No licensing fees, commercial royalties, or official vendor purchases are required for educational or scholarly use. Researchers utilizing the instrument are expected to cite the original validation literature (Buunk, 1980a; Fishbein & Ajzen, 1975) in all derived reports and scholarly communications. Inquiries concerning proprietary, industrial, or commercial applications may be directed to Dr. Bram Buunk at the University of Groningen.

References

• Bell, R. R., Turner, S., & Rosen, L. (1975). A multivariate analysis of female extramarital coitus. Journal of Marriage and the Family, 37(2), 375–384. https://doi.org/10.2307/350972
• Buunk, B. (1980a). Extramarital sex in the Netherlands: Motivations in social and marital context. Alternative Lifestyles, 3(1), 11–39. https://doi.org/10.1007/BF01082187
• Buunk, B. (1980b). Sexually open marriages: Ground rules for countering potential threats to marriage. Alternative Lifestyles, 3(3), 312–328. https://doi.org/10.1007/BF01082001
• Buunk, B. (1981). De samenhang van attitudes en sociale normen met de intentie tot buitenechtelijke sex [The relationships between extramarital behavioral intentions and attitudes and social norms]. Nederlands Tijdschrift voor de Psychologie, 36, 165–170.
• Buunk, B. (1982). Anticipated sexual jealousy: Its relationships to self-esteem, dependency and reciprocity. Personality and Social Psychology Bulletin, 8(2), 310–316. https://doi.org/10.1177/0146167282082019
• Fishbein, M., & Ajzen, I. (1975). Belief, attitude, intention, and behavior: An introduction to theory and research. Addison-Wesley.
• Frenken, J. (1976). Afkeer van seksualiteit [Aversion to sexuality]. Van Loghum Slaterus.
• Guttman, L. (1944). A basis for scaling qualitative data. American Sociological Review, 9(2), 139–150. https://doi.org/10.2307/2086306

13. Items of the Scale (Questionnaire)