Investment Model Scale

1. Abstract

The Investment Model Scale (IMS) is a seminal psychometric assessment instrument developed by Caryl E. Rusbult, John M. Martz, and Christopher R. Agnew (1998) to operationalize the key constructs of Rusbult’s Interdependence-based Investment Model of commitment processes. Rooted in social exchange theory and Harold Kelley and John Thibaut’s interdependence theory, the scale systematically evaluates four core relational dimensions: Satisfaction Level, Quality of Alternatives, Investment Size, and Commitment Level. The instrument is engineered using both concrete facet-level items—which assess specific relational domains such as intimacy, companionship, sexual fulfillment, security, and emotional involvement—and global items designed to capture broad psychological orientations. Administered typically via a 9-point Likert-type scale ranging from 0 (Do Not Agree At All) through 4 (Agree Somewhat) to 8 (Agree Completely), the instrument yields discrete subscale scores that model how dependence translates into subjective commitment and subsequent relationship persistence. Across decades of empirical replication, the IMS has exhibited outstanding psychometric properties, featuring Cronbach’s alpha coefficients consistently exceeding .80 to .95 across subscales, well-defined factor structures confirmed via exploratory and confirmatory factor analyses, robust convergent validity with parallel dyadic indicators, and extraordinary predictive validity regarding relationship stability, relational maintenance behaviors, accommodation, and dyadic dissolution. This article provides an exhaustive, academic-grade review of the scale’s theoretical architecture, measurement models, structural validity, psychometric properties, and administrative protocols across clinical, social psychological, and organizational domains.

2. Keywords

Investment Model Scale, Interdependence Theory, Relationship Commitment, Relationship Satisfaction, Quality of Alternatives, Investment Size, Relationship Stability, Caryl Rusbult, Romantic Relationships, Dyadic Persistence

3. Authors

The Investment Model Scale was authored by an influential team of social psychologists specializing in close relationships, interpersonal dynamics, and social exchange:

• Caryl E. Rusbult, Ph.D. (1952–2010): Formerly Professor and Chair of the Department of Social Psychology at Vrije Universiteit Amsterdam and previously Professor of Psychology at the University of North Carolina at Chapel Hill. Rusbult is widely recognized as one of the preeminent relationship scientists of the twentieth century, famed for pioneering the Investment Model, researching accommodation processes, and examining forgiveness and sacrifice in close relationships.
• John M. Martz, Ph.D.: Researcher and clinical psychologist whose foundational collaborative work with Rusbult focused on interpersonal commitment, clinical dynamics of relationships, and the structural factors that compel individuals to remain in non-optimal or abusive partnerships.
• Christopher R. Agnew, Ph.D.: Professor of Psychological Sciences and Associate Vice President for Research at Purdue University. Agnew is a leading expert on interpersonal relationships, social influence, relational commitment, and health behaviors within interpersonal contexts.

Institutional origins of the instrument trace back to the Department of Psychology at the University of North Carolina at Chapel Hill and the Department of Psychological Sciences at Purdue University. Inquiries regarding archival permissions and theoretical frameworks are commonly addressed through contemporary academic literature originating from relational interdependence laboratories worldwide.

4. Purpose

The overarching purpose of the Investment Model Scale is to assess the psychological mechanisms that govern relational persistence, longevity, and stability. Historically, early relationship research operated under the tacit assumption that relationship stability was primarily a direct function of personal happiness or satisfaction. However, clinical and empirical observations repeatedly challenged this simplistic hedonistic model: individuals frequently remain in relationships that are unhappy, distressed, or even physically and emotionally abusive, while others terminate subjectively pleasant partnerships. Rusbult formulated the Investment Model to resolve this paradox by delineating a critical conceptual distinction between satisfaction (an affective or evaluative state of positive valence) and commitment (a psychological state representing long-term orientation, intent to persist, and feelings of psychological attachment).

The IMS operationalizes the mathematical and theoretical premises of Interdependence Theory by evaluating the three proximal antecedents of commitment: (1) Satisfaction Level, reflecting the degree to which an individual perceives that a partner gratifies essential emotional, physical, and relational needs relative to an internal benchmark or comparison level; (2) Quality of Alternatives, capturing the perceived desirability and availability of potential options outside the focal relationship, including dating other people, expanding platonic networks, or thriving in solitary autonomy; and (3) Investment Size, gauging the magnitude and importance of the resources—both intrinsic (e.g., self-disclosure, time, emotional effort) and extrinsic (e.g., shared material possessions, mutual social networks, intertwined identities)—that have become intrinsically bound to the partnership and would be severely diminished or lost upon termination.

In research contexts, the scale serves as a standard metric to forecast marital stability, dating dissolution, sacrifice, accommodation during relational conflict, derogation of alluring alternative partners, and psychological distress following romantic dissolution. In clinical and marital counseling settings, the IMS functions as a diagnostic framework that enables clinicians to map a client’s or couple’s structural dependencies. It clarifies whether a relationship is sustained primarily by mutual positive attraction (high satisfaction), structural entrapment (low satisfaction, poor alternatives, high investments), or precarious volatility (low investment, high quality of alternatives). Beyond romantic dyads, the IMS has been broadly generalized to examine organizational commitment, employee turnover, customer loyalty in consumer psychology, athletic team adherence, and persistence in medical treatment regimens.

5. Psychological Construct

The psychological construct underlying the Investment Model Scale represents a multidimensional model of relational interdependence. The framework posits that commitment functions as the central, proximal engine of relationship maintenance behaviors and ultimate persistence, mediated by three discrete cognitive and affective evaluations.

Satisfaction Level

Satisfaction reflects an individual’s positive versus negative affective evaluation of their relationship. Grounded in Thibaut and Kelley’s (1959) concept of the Comparison Level ($CL$), satisfaction is determined by comparing the actual outcomes received from the relationship (rewards minus costs) against an individual’s internalized standard of what constitutes an acceptable partnership. When relational experiences exceed the $CL$, satisfaction is high. Within the IMS, satisfaction is assessed both via concrete facet evaluations—such as intimacy, companionship, sexual needs, emotional security, and reciprocal emotional involvement—and global evaluations of happiness, perfection, and superiority relative to the relationships of peers.

Quality of Alternatives

Quality of alternatives is anchored in the Comparison Level for Alternatives ($CL_{alt}$), defined as the lowest level of relational outcomes an individual will accept in light of available alternative opportunities. Crucially, alternatives do not merely refer to other prospective romantic or sexual partners; they encompass a comprehensive spectrum of alternative states, including spending more time with friends or family, investing in career ambitions, or enjoying singlehood and autonomy. High quality of alternatives undermines dependence: if an individual perceives that their needs for companionship, intimacy, and security can be readily satisfied outside the current partnership, their reliance on the current partner diminishes significantly.

Investment Size

Investment size refers to the magnitude and significance of the resources attached directly or indirectly to the relationship. Investments create structural inertia or “sunk costs” that make leaving the dyad significantly more costly and psychologically distressing. The construct encompasses two primary forms:

• Intrinsic Investments: Resources put directly into the partnership that cannot be reclaimed, such as self-disclosure of intimate vulnerabilities, time, emotional energy, and personal effort.
• Extrinsic Investments: External resources, identities, and structural ties that were initially independent but have become inextricably intertwined with the relationship over time, including shared bank accounts, joint real estate, mutual friendships, shared memories, in-law relationships, and a fused sense of personal self-concept (relational self-construal).

Commitment Level

Commitment is defined as a complex subjective psychological state that encapsulates three fundamental components: (a) a long-term temporal horizon (viewing the partnership as continuing far into the future), (b) an intent to persist (a deliberate psychological determination to maintain the bond), and (c) psychological attachment (experiencing emotional connection such that an individual’s personal well-being is deeply tied to the partner’s well-being and the survival of the union). In Rusbult’s model, commitment mediates the effects of satisfaction, alternatives, and investments on actual relationship maintenance behaviors, including accommodation in response to partner betrayal, cognitive positive illusions, and active relationship persistence.

6. Theoretical Framework

The Investment Model is an extension of Interdependence Theory, originally formulated by social psychologists Harold Kelley and John Thibaut in 1959 and significantly expanded in 1978. Interdependence theory uses mathematical game theory matrices and exchange principles to analyze how interpersonal patterns of interaction shape human cognition, affect, and behavior. At its core, the theory posits that interaction between two persons ($A$ and $B$) is a function of the joint outcomes made possible by their respective behavioral repertoires.

Rusbult expanded this foundation by integrating principles from Social Exchange Theory (Homans, 1961; Blau, 1964) and organizational turnover models. While Thibaut and Kelley focused extensively on the immediate reward-cost payoff structure and the baseline concepts of $CL$ and $CL_{alt}$, Rusbult identified that dependence—the degree to which an individual needs a relationship for personal fulfillment—is not merely an equation balancing present rewards against outside choices. Rather, dependence is heavily stabilized by past investments that would be relinquished upon termination.

The theoretical model is formalized through the following structural axioms:

1. Dependence Architecture: Dependence ($D$) is a joint function of satisfaction, quality of alternatives, and investment size:
   $$\text{Dependence} = f(\text{Satisfaction}, -\text{Alternatives}, +\text{Investments})$$
   An individual is highly dependent on a partner when the relationship provides high rewards, outside options are perceived as barren or unappealing, and immense personal resources are sunk into the union.
2. Commitment as the Cognitive Translation of Dependence: Dependence does not remain an abstract structural state; it becomes subjectively experienced as psychological commitment. Commitment represents the internal psychological manifestation of structural dependence.
3. Transformation of Motivation: Commitment initiates what Kelley and Thibaut termed the “transformation of motivation.” When individuals become committed, they cease to act purely on the basis of “given” self-interested preferences (immediate, selfish impulses) and instead evaluate actions through an “effective” relational lens (the broader welfare of the relationship). This transformation explains why committed individuals exhibit costly pro-relationship maintenance behaviors: accommodating a partner’s destructive behavior rather than retaliating in kind (voice/loyalty rather than exit/neglect), sacrificing personal desires for the partner’s benefit, systematically derogating physically attractive alternative partners, and nurturing cognitively biased, idealized illusions regarding their partner’s virtues.

7. Validity

The psychometric validity of the Investment Model Scale has been extensively documented in original psychometric investigations by Rusbult, Martz, and Agnew (1998) and corroborated by a massive meta-analysis conducted by Le and Agnew (2003), spanning 137 studies and over 25,000 participants.

Construct and Structural Validity

Construct validity has been verified across multiple cross-sectional, longitudinal, and experimental designs. Rusbult et al. (1998) demonstrated through series of regression and structural equation models that the three predicted antecedents account for between 60% and 80% of the variance in relationship commitment ($R^2$ values typically ranging from .61 to .80). As theoretically predicted, Satisfaction Level and Investment Size exhibit strong, statistically significant positive path coefficients to Commitment, whereas Quality of Alternatives consistently produces significant negative path coefficients.

Convergent and Discriminant Validity

The IMS exhibits outstanding convergent validity through substantial correlations with established relationship metrics:

• The Satisfaction subscale correlates highly with the Dyadic Adjustment Scale (DAS; Spanier, 1976) and the Relationship Assessment Scale (RAS; Hendrick, 1988), with coefficients frequently exceeding $r = .70$.
• Commitment demonstrates strong positive convergence with the Inclusion of Other in the Self (IOS) Scale (Aron, Aron, & Smollan, 1992) and Norton’s (1983) Quality Marriage Index.
• Discriminant validity has been demonstrated by showing that the four constructs are not merely redundant indicators of positive sentiment. For instance, in factor analyses, items assessing Investment Size load on distinct latent dimensions from Satisfaction and Commitment. Furthermore, empirical studies on clinical populations, including battered women residing in domestic abuse shelters (Rusbult & Martz, 1995), showed that women who returned to their abusers exhibited low satisfaction but high investment size and extremely limited economic and housing alternatives—confirming that the scale cleanly disentangles affective enjoyment from structural entrapment.

Predictive Validity

The scale possesses remarkable predictive utility. In longitudinal studies tracking dating and married couples over periods ranging from six months to several years, baseline Commitment Level measured by the IMS is one of the single best psychometric predictors of whether a couple remains together or dissolves ($p < .001$). Meta-analytic findings (Le & Agnew, 2003) confirmed that commitment was a robust predictor of relational persistence ($r = .47$). In addition, the subscales significantly predict behavioral markers such as constructive accommodation during dyadic problem-solving tasks, frequency of self-sacrifice, and spontaneous cognitive devaluation of attractive external alternatives.

8. Reliability

The Investment Model Scale displays exceptional internal consistency and temporal reliability across diverse demographic groups, cultural backgrounds, and relationship categories (dating, cohabiting, married, and same-sex partnerships).

Internal Consistency

In the original validation studies across three independent samples published by Rusbult, Martz, and Agnew (1998), the Cronbach’s alpha ($\alpha$) coefficients for both the facet-based and global subscales consistently exceeded established psychometric benchmarks:

• Satisfaction Level Subscale: Displays extraordinarily high internal consistency, with alpha coefficients across developmental samples reported at $\alpha = .92$, $.95$, and $.94$ for global items, and composite reliabilities consistently hovering around $.87$ to $.94$.
• Quality of Alternatives Subscale: Demonstrates strong internal reliability, yielding Cronbach’s alphas of $\alpha = .82$, $.85$, and $.88$ across validation studies.
• Investment Size Subscale: Yields robust alpha coefficients ranging from $\alpha = .82$ to $.84$ across samples, indicating strong internal cohesion despite the heterogeneous nature of human investments (e.g., emotional secrets vs. tangible shared items).
• Commitment Level Subscale: Achieves exceptional internal consistency metrics across trials, registering $\alpha = .91$, $.91$, and $.95$ across original cohorts, and maintaining $\alpha ge .90$ in subsequent cross-cultural adaptations.

Test-Retest Stability

Longitudinal assessments reveal high stability coefficients over short intervals (e.g., two- to four-week test-retest correlations $r > .80$), reflecting the enduring nature of structural commitment orientations. Over longer durations (e.g., six months to two years), test-retest coefficients display systematic and theoretically predictable variations, showing sensitivity to major life transitions, relationship violations, and natural dyadic deterioration while maintaining overall structural stability.

9. Factor Analysis

The internal structural validity of the Investment Model Scale has been rigorously tested using both Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA).

Exploratory Factor Analysis (EFA)

During scale development, Rusbult and colleagues subjected the candidate items across both facet and global categories to principal components analysis followed by oblique (Promax) and orthogonal (Varimax) rotations. The analyses unequivocally isolated four distinct, clean eigenvalues exceeding the Kaiser-Guttman criterion of 1.0, with the scree plot confirming a steep four-factor elbow. Items exhibited high primary factor loadings (overwhelmingly exceeding .60, with many global items loading between .75 and .90) and remarkably negligible cross-loadings (consistently below .25), affirming the distinctiveness of Satisfaction, Alternatives, Investments, and Commitment.

Confirmatory Factor Analysis (CFA)

Subsequent structural equation modeling and CFA paradigms have examined competing structural topologies to evaluate whether the data are best characterized by a single undifferentiated relationship health factor, a three-factor model, or the hypothesized four-factor correlated model. CFA results robustly favor the four-factor correlated latent model:

• Goodness of Fit: The four-factor correlated specification yields exceptional fit indices across diverse samples, satisfying standard empirical criteria: Chi-Square to degrees of freedom ratio ($\chi^2/df < 2.5$), Comparative Fit Index ($\text{CFI} ge .95$), Tucker-Lewis Index ($\text{TLI} ge .94$), and Root Mean Square Error of Approximation ($\text{RMSEA} le .05$ to $.06$).
• Hierarchical Structural Models: When commitment is specified as an endogenous latent variable predicted by the three exogenous latent variables (Satisfaction, Alternatives, and Investments), the model exhibits optimal structural parameters, with significant directional path coefficients confirming the mediation structure dictated by interdependence theory.

10. Instrument / Measurement Tool

The Investment Model Scale is an efficiently structured self-report survey instrument designed to be completed in approximately 10 to 15 minutes. It can be administered via pencil-and-paper format or computerized online testing platforms.

• Test Type: Multidimensional Self-Report Questionnaire / Psychometric Scale.
• Target Population: Individuals currently engaged in ongoing romantic relationships (e.g., casual dating, steady dating, engaged, cohabiting, married, civil unions). Also adaptable for organizational, athletic, or platonic contexts.
• Instrument Structure:
  • Global Subscales: Broad, comprehensive summary items capturing each overarching theoretical construct (typically 5 items for Satisfaction, 5–6 items for Alternatives, 5–6 items for Investment Size, and 7 items for Commitment Level).
  • Facet Subscales: Specific, concrete items evaluating five foundational relational domains: Intimacy, Companionship, Sexual Fulfillment, Security, and Emotional Involvement. Facet items are evaluated separately for current partner fulfillment versus alternative fulfillments.
• Response Scale:
  • 9-point Likert-type anchor format: 0 = Do Not Agree At All, 1, 2, 3, 4 = Agree Somewhat, 5, 6, 7, 8 = Agree Completely.
  • Facet need fulfillment sections occasionally incorporate comparative anchor framing (e.g., evaluating how well specific needs are satisfied by the current partner versus potential alternatives).
• Scoring and Computational Rules:
  • Reverse Coding: Identified negative items within the Commitment subscale (e.g., items stating that the relationship is likely to end soon, or that one would not feel upset if it ended) must be reverse scored ($X_{\text{reversed}} = 8 – X$) prior to composite calculation.
  • Subscale Scores: Calculated by computing the mathematical mean (or sum) of the corresponding items for each respective dimension: Satisfaction Level, Quality of Alternatives, Investment Size, and Commitment Level.
  • Predictive Regression Equation: Evaluated using standard structural regression:
    $$\text{Commitment} = \beta_0 + \beta_1(\text{Satisfaction}) – \beta_2(\text{Alternatives}) + \beta_3(\text{Investments})$$

11. Permissions & Fee and Test Year

The Investment Model Scale was formally published in its standardized psychometric form in 1998 in the journal Personal Relationships by Caryl E. Rusbult, John M. Martz, and Christopher R. Agnew. Consistent with Dr. Rusbult’s dedication to advancing relationship science, the instrument was placed in the public domain for academic, scientific, and educational research purposes. Researchers and psychological practitioners may utilize, administer, and translate the scale without paying licensing fees, provided that appropriate scholarly attribution and bibliographic citation are given to the original authors.

Commercial utilization, packaging within proprietary fee-generating clinical software, or broad commercial publishing requires permission from the copyright holders (the International Association for Relationship Research and Cambridge University Press, or the scale’s surviving authors). Detailed archival documentation, scoring manuals, and adaptation guides were historically maintained via Dr. Rusbult’s academic repository at Vrije Universiteit Amsterdam and through Dr. Christopher Agnew’s research portal at Purdue University.

12. References

The following peer-reviewed publications and foundational works provide the conceptual, empirical, and mathematical underpinnings of the Investment Model Scale:

• Aron, A., Aron, E. N., & Smollan, D. (1992). Inclusion of Other in the Self Scale and the structure of interpersonal closeness. Journal of Personality and Social Psychology, 63(4), 596–612. https://doi.org/10.1037/0022-3514.63.4.596
• Blau, P. M. (1964). Exchange and power in social life. John Wiley & Sons.
• Hendrick, S. S. (1988). A generic measure of relationship satisfaction. Journal of Marriage and the Family, 50(1), 93–98. https://doi.org/10.2307/352130
• Homans, G. C. (1961). Social behavior: Its elementary forms. Harcourt, Brace & World.
• Kelley, H. H., & Thibaut, J. W. (1978). Interpersonal relations: A theory of interdependence. John Wiley & Sons.
• Le, B., & Agnew, C. R. (2003). Need fulfillment and persistence in close relationships: Does commitment mediate the relationship between need fulfillment and persistence? Personal Relationships, 10(2), 227–244. https://doi.org/10.1111/1475-6811.00047
• Norton, R. (1983). Measuring marital quality: A critical look at the dependent variable. Journal of Marriage and the Family, 45(1), 141–151. https://doi.org/10.2307/351302
• Rusbult, C. E. (1980). Commitment and satisfaction in romantic associations: A test of the investment model. Journal of Experimental Social Psychology, 16(2), 172–186. https://doi.org/10.1016/0022-1031(80)90007-4
• Rusbult, C. E. (1983). A longitudinal test of the investment model: The development (and deterioration) of satisfaction and commitment in heterosexual involvements. Journal of Personality and Social Psychology, 45(1), 101–117. https://doi.org/10.1037/0022-3514.45.1.101
• Rusbult, C. E., Drigotas, S. M., & Verette, J. (1994). The investment model: An interdependence analysis of commitment processes and relationship maintenance phenomena. In D. J. Canary & L. Stafford (Eds.), Communication and relational maintenance (pp. 115–139). Academic Press.
• Rusbult, C. E., & Farrell, D. (1983). A longitudinal test of the investment model: The impact on job satisfaction, job commitment, and turnover of variations in rewards, costs, alternatives, and investments. Journal of Applied Psychology, 68(3), 429–438. https://doi.org/10.1037/0021-9010.68.3.429
• Rusbult, C. E., & Martz, J. M. (1995). Remaining in an abusive relationship: An investment model analysis of nonvoluntary dependence. Personality and Social Psychology Bulletin, 21(6), 558–571. https://doi.org/10.1177/0146167295216002
• Rusbult, C. E., Martz, J. M., & Agnew, C. R. (1998). The Investment Model Scale: Measuring commitment level, satisfaction level, quality of alternatives, and investment size. Personal Relationships, 5(4), 357–391. https://doi.org/10.1111/j.1475-6811.1998.tb00177.x
• Spanier, G. B. (1976). Measuring dyadic adjustment: New scales for assessing the quality of marriage and similar dyads. Journal of Marriage and the Family, 38(1), 15–28. https://doi.org/10.2307/350547
• Thibaut, J. W., & Kelley, H. H. (1959). The social psychology of groups. John Wiley & Sons.

13. Items of the Scale (Questionnaire)