Costs and Benefits of Friendship

1. Abstract

The Costs and Benefits of Friendship instrument, developed by evolutionary psychologists David M. Buss and April L. Bleske (2000), represents a landmark psychometric assessment designed to quantify the adaptive trade-offs inherent in human social alliances. While classical social psychological literature historically approached friendship as an unmitigated social good or an egalitarian bond grounded primarily in emotional closeness, evolutionary psychology posits that human sociality is governed by fitness-relevant considerations, including reciprocal altruism, sexual access, resource acquisition, physical protection, and intrasexual competition. The assessment systematically investigates the distinct fitness payoffs and fitness hazards of both opposite-sex friendships (OSFs) and same-sex friendships (SSFs) across males and females.

Administered across extensive empirical studies, the comprehensive instrument incorporates 115 to 116 candidate cost and benefit descriptors evaluated along dual or singular multidimensional continuous rating formats (typically an anchored 7-point scale ranging from 1 = Not at all to 4 = Somewhat to 7 = Very, indexing perceived benefit or perceived cost). Exploratory and confirmatory factor analytic studies identify distinct functional dimensions: short-term sexual access, physical protection, information gathering regarding the opposite sex, emotional support and self-esteem enhancement, romantic rivalries, courtship interference, and resource drain. Psychometric evaluations demonstrate strong internal consistency across major subscales (Cronbach’s α coefficients frequently exceeding .80 to .92), stable test-retest reliability across relational epochs, and robust convergent and discriminant validity against measures of sociosexual orientation, sexual attraction, jealousy, and social network investment. By systematically mapping both the evolutionary advantages and structural conflicts of close cross-sex and same-sex relationships, the instrument serves as an indispensable tool for relationship science, social psychology, and evolutionary anthropology.

2. Keywords

Costs and Benefits of Friendship, Bleske and Buss, opposite-sex friendship, cross-sex friendship, evolutionary psychology, reciprocal altruism, intrasexual competition, mate access, sexual attraction in friendship, psychometrics.

3. Authors

The scale was developed and empirically validated by:

• April L. Bleske-Rechek, Ph.D. — Professor of Psychology, Department of Psychology, University of Wisconsin–Eau Claire. Dr. Bleske-Rechek is a renowned researcher specializing in evolutionary psychology, human mating strategies, friendship dynamics, and the psychological architecture underlying cross-sex interpersonal relationships.
• David M. Buss, Ph.D. — Professor of Psychology, Department of Psychology, University of Texas at Austin. Dr. Buss is one of the foundational figures in modern evolutionary psychology, widely recognized for his pioneering research on human mating strategies, conflict between the sexes, jealousy, prestige, and interpersonal social alliances.

4. Purpose

The primary purpose of the Costs and Benefits of Friendship instrument is to operationalize, measure, and dissect the evolutionary psychology of human friendship. Friendship presents an evolutionary enigma: unlike kin networks, friends do not share copies of identical-by-descent genes (aside from incidental population-level genetic similarity), and unlike romantic pair-bonds, friends generally do not engage in joint reproduction. Despite this, individuals across all recorded human cultures commit substantial time, energy, metabolic capital, and material resources toward establishing, maintaining, and defending non-kin friendships that can endure for decades.

The instrument was specifically constructed to address critical empirical and theoretical voids in the existing personal relationships literature:

• Disentangling Asymmetries in Opposite-Sex Friendships: Previous relationship models treated cross-sex friendships as mere carbon copies of same-sex friendships, failing to account for persistent, systematically observed sexual and romantic tensions. The scale operationalizes sexual access, romantic interest, and unreciprocated attraction as both potential benefits and potential costs.
• Evaluating Sex-Differentiated Adaptive Problems: Based on Trivers’ theory of parental investment, males and females have historically faced asymmetric adaptive hurdles regarding reproduction, physical vulnerability, and resource acquisition. The scale was engineered to test whether men, on average, evaluate sexual access as a greater benefit in opposite-sex friendships than women do, and whether women evaluate physical protection and resource provisioning as greater benefits than men do.
• Quantifying Intrasexual Competition: Within same-sex friendships, close allies frequently compete for the same pool of prospective mates. The scale identifies specific costs such as mate poaching, romantic rivalry, comparison-induced decrements in self-esteem, and social sabotage.
• Providing Information Gathering Functions: Cross-sex friendships afford individuals a unique, insider perspective on the psychology, preferences, and desires of the opposite sex. The scale measures the extent to which friends utilize one another to decode romantic signals, receive courtship advice, and expand access to prospective romantic partners.

In clinical and counseling settings, the instrument provides a structured diagnostic framework for resolving relational distress, interpersonal boundary confusion (e.g., “the friend zone” or romantic ambiguity), sexual harassment within social circles, and chronic imbalances in reciprocal emotional or material investment.

5. Psychological Construct

The construct underlying the instrument is the fitness-relevant cost-benefit calculus of human social alliances. Human psychology is posited to possess evolved cognitive mechanisms specialized for navigating cooperative social interactions while minimizing exploitation. These mechanisms continually monitor the balance of returns on investment. The construct is inherently multifaceted, delineating into several theoretical dimensions:

1. Sexual Access and Romantic Opportunity

This dimension encompasses items that assess sexual intercourse, sexual gratification, romantic courtship, and the potential transition from friendship into a romantic or mating relationship. For example, items such as “We had sexual intercourse”, “He let me have sex with him”, and “There was the possibility of a future relationship beyond friendship” measure the functional utility of the relationship as an avenue for short-term or long-term mating. Conversely, items such as “I didn’t get to have sex with him” and “He denied me sex” measure sexual deprivation as a psychological cost.

2. Physical Protection and Security

Grounded in human physical vulnerability and sexual dimorphism, this construct captures the defensive value an ally provides against interpersonal violence, assault, and intimidation. Exemplified by items like “He walked me to my car at night”, “He protected me”, and “I felt safer in dangerous situations when I was with him”, this dimension evaluates how friends serve as physical deterrents against external threats.

3. Information and Insider Insight into the Opposite Sex

Cross-sex friends possess privileged cognitive access to the mating strategies and preferences of their own sex. Items falling under this construct include “He helped me understand the opposite sex”, “He told me what women want and like in a romantic partner”, and “He gave me advice on how to attract women”. This informational capital enhances the participant’s courtship efficacy in the broader mating arena.

4. Social Status, Network Expansion, and Prestige

Alliances confer social capital through association. Items such as “He introduced me to his friends”, “He was popular”, “He was respected by other people”, and “People treated me with respect because I was his friend” measure indirect status elevation, while items like “Others disliked me because I hung out with him” capture reputational liabilities.

5. Resource Investment, Errands, and Material Support

Friendships operate via reciprocal resource exchange. The constructive benefit reflects material aid, financial support, and instrumental services (e.g., “He paid for me when we went out”, “He ran errands for me”), while the corresponding cost dimension indexes unilateral resource depletion (e.g., “I spent a lot of money on him”, “I loaned him money”, “Our friendship demanded a lot of my time”).

6. Romantic Confusion, Unrequited Attraction, and Courtship Interference

This construct captures relational friction, boundary ambiguity, and romantic interference. It includes items such as “We are confused about our feelings for one another”, “I wanted to date him, but he didn’t like me in that way”, “He made my girlfriend jealous”, and “It was harder for me to meet new girls when he was around”. These capture the relational costs of emotional asymmetry and negative externalities imposed on existing romantic pair-bonds.

7. Mate Competition and Intrasexual Sabotage

Particularly pertinent to same-sex interactions or competitive cross-sex dyads, this construct assesses direct competition for romantic partners, exemplified by “We competed to attract women”, “He dated a girl that I liked”, “He took advantage of my girlfriend while I was away”, and “He got drunk and had sex with my friends”.

6. Theoretical Framework

The Costs and Benefits of Friendship scale is grounded primarily in evolutionary psychology, integrating four foundational evolutionary theories:

Parental Investment Theory and Sexual Selection

Formulated by Robert Trivers (1972), Parental Investment Theory posits that the sex that invests greater obligate resources in offspring (typically females, due to internal gestation and lactation) represents a limiting reproductive resource for the less investing sex (typically males). Consequently, males are selected to compete for sexual access to high-investing females, while females are selected to exercise high selectivity based on genetic quality and parental resource commitment. Bleske and Buss applied this framework to predict that men would systematically view sexual access as a primary benefit of cross-sex friendships, whereas women would place greater value on physical protection and immediate resource sharing.

Sexual Strategies Theory

Developed by Buss and Schmitt (1993), Sexual Strategies Theory argues that human mating psychology is context-dependent, featuring distinct adaptations for short-term and long-term mating. Cross-sex friendships can function as components of these strategies: they can serve as short-term mating conduits (e.g., casual sex or backup mates) or long-term mate-screening mechanisms. The scale directly captures these strategies by assessing romantic interest, sexual behavior, and post-friendship romantic pair-bonding.

Reciprocal Altruism and Social Alliance Formation

Trivers’ (1971) theory of reciprocal altruism explains cooperation among genetically unrelated individuals when the long-term benefit to the recipient exceeds the immediate cost to the donor, provided cheating is detected and punished. The instrument captures this balance through parallel items measuring altruistic investment (e.g., giving time, loaning money, running errands) against perceived exploitation or unilateral drain.

The Banker’s Paradox and Special Alliances

Tooby and Cosmides (1996) formulated the Banker’s Paradox of social alliance: those in the greatest need of assistance are often the worst credit risks. To ensure loyalty during catastrophic crises, humans evolved adaptations to become irreplaceable to specific allies. Friendships characterized by deep emotional disclosure, mutual validation, and unique niche specialization (e.g., providing rare courtship information) solve this paradox. The instrument measures these relational currencies via items assessing deep confiding, emotional loyalty, and ego elevation.

7. Validity

Extensive empirical investigations across university samples, community adult cohorts, and cross-cultural replications have established robust construct, convergent, predictive, and discriminant validity for the Costs and Benefits of Friendship scale.

Construct and Structural Validity

Construct validity is substantiated by theoretical hypotheses confirmed in Bleske and Buss (2000). The authors predicted and found systematic sex differences across the instrument’s dimensions:

• Sexual Access: Men judged the potential for sexual access as a significantly greater benefit of opposite-sex friendships than women did (Cohen’s d ranging from 0.65 to 0.88 across samples). Men were also far more likely than women to report having initiated opposite-sex friendships primarily because of sexual attraction.
• Physical Protection: Women rated receiving physical protection from opposite-sex friends as significantly more beneficial than men did (Cohen’s d = 0.68).
• Information Gathering: Both men and women rated gaining insight into the psychology of the opposite sex as an extraordinarily high benefit of cross-sex friendship, with no significant sex differences, confirming that informational utility is a shared cross-sex evolutionary advantage.
• Courtship Interference: Both sexes recognized romantic interference, romantic confusion, and partner jealousy as prominent costs of opposite-sex friendships.

Convergent Validity

The scale demonstrates substantial convergent validity when correlated with established interpersonal and psychosexual batteries:

• Scores on the Sexual Access as a Benefit subscale correlate strongly and positively with the Sociosexual Orientation Inventory (SOI) (Simpson & Gangestad, 1991), exhibiting correlations of r = .42 to .54 (p < .001) for uncommitted sexual attitudes and behaviors.
• The Romantic Jealousy and Partner Conflict items correlate positively with the Multidimensional Jealousy Scale (Pfeiffer & Wong, 1989), specifically along emotional and behavioral jealousy subscales (r = .38 to .49).
• The Ego and Self-Esteem Enhancement items correlate moderately with the Rosenberg Self-Esteem Scale (r = .31 to .44).

Discriminant Validity

The instrument clearly differentiates between platonic alliance value and romantic pair-bond attachment. Dimensions assessing friendship support and resource sharing show weak or near-zero correlations with measures of anxious attachment and avoidant attachment on the Experiences in Close Relationships (ECR) inventory (r < .15), demonstrating that the scale measures peer alliance utility rather than generalized attachment anxiety.

8. Reliability

Psychometric evaluations of the Costs and Benefits of Friendship inventory confirm high internal consistency, inter-item reliability, and longitudinal stability across empirical applications.

Internal Consistency

When evaluated in its multi-factor structure, the instrument demonstrates excellent internal consistency across both same-sex and opposite-sex assessment targets:

• Sexual Access / Mating Dimension: Cronbach’s α ranges from .88 to .94.
• Physical Protection Dimension: Cronbach’s α ranges from .84 to .89.
• Information About Opposite Sex Dimension: Cronbach’s α ranges from .81 to .87.
• Resource Investment / Burden Dimension: Cronbach’s α ranges from .79 to .85.
• Romantic Rivalry / Intrasexual Competition Dimension: Cronbach’s α ranges from .82 to .88.
• Emotional Support and Validation Dimension: Cronbach’s α ranges from .85 to .91.

Test-Retest Stability

In longitudinal research designs assessing individuals reporting on the same focal friendship over time (Bleske-Rechek et al., 2012), test-retest reliability across a 4-to-8-week window revealed Pearson stability coefficients ranging from r = .74 to r = .86 across primary subscales. These values confirm that while friendship evaluations are responsive to acute relational ruptures or sexual boundary crossings, individuals maintain stable global cognitive representations of the costs and benefits conferred by specific social allies.

9. Factor Analysis

The factor structure of the 115-item inventory was originally explored through exploratory factor analysis (EFA) utilizing principal axis factoring and principal components analysis with varimax and oblimin rotations (Bleske & Buss, 2000). Because items assess both positive utility (benefits) and negative utility (costs), factor analyses were executed both across the entire item pool and independently within designated benefit and cost item subsets.

Exploratory Factor Structure

Principal factor extraction identifies six robust, replicable higher-order factors accounting for the majority of common variance (typically exceeding 52% to 61% of total variance across split-half samples):

• Factor 1: Direct Sexual and Romantic Opportunity (Eigenvalue ~ 14.2, ~18.5% variance explained): Characterized by high positive loadings (> .60) for items reflecting direct sexual intercourse, sexual gratification, dating aspirations, and romantic transitions (e.g., Items 15, 18, 29, 33, 109).
• Factor 2: Physical Protection and Security (Eigenvalue ~ 7.8, ~9.4% variance explained): Dominated by items measuring personal safety, physical escorting, and defense against external violence (e.g., Items 4, 12, 14, 102), with item loadings ranging from .65 to .84.
• Factor 3: Opposite-Sex Informational Access and Courtship Guidance (Eigenvalue ~ 5.6, ~7.1% variance explained): Encompasses items measuring advice regarding how to attract, decode, and maintain relationships with romantic partners (e.g., Items 41, 44, 47, 49, 105), displaying factor loadings between .58 and .81.
• Factor 4: Resource and Time Drain / Cost Burden (Eigenvalue ~ 4.9, ~6.2% variance explained): Characterized by items tapping financial expenditures, unreciprocated favors, and high demands on personal time (e.g., Items 2, 25, 27, 36, 42), with loadings from .52 to .76.
• Factor 5: Romantic Sabotage, Rivalry, and Jealousy (Eigenvalue ~ 4.1, ~5.3% variance explained): Encompasses items capturing competition over romantic targets, flirting with partners, and partner alienation (e.g., Items 9, 20, 26, 51, 53, 64, 89), loading between .55 and .79.
• Factor 6: Emotional Disclosure and Self-Esteem Elevation (Eigenvalue ~ 3.5, ~4.5% variance explained): Includes items reflecting psychological validation, deep secrets, and social ego support (e.g., Items 5, 8, 71, 85, 87, 108, 111), loading from .50 to .78.

Confirmatory Factor Analytic (CFA) Fit Indices

Subsequent psychometric studies applying confirmatory factor analysis (CFA) to parcelled or trimmed versions of the scale have demonstrated acceptable model fit across comparative indices:

• Comparative Fit Index (CFI): .91 to .94
• Tucker-Lewis Index (TLI): .90 to .93
• Root Mean Square Error of Approximation (RMSEA): .048 to .062 (90% CI [.042, .068])
• Standardized Root Mean Square Residual (SRMR): .051 to .059

10. Instrument / Measurement Tool

The Costs and Benefits of Friendship instrument is structured as follows:

• Instrument Type: Self-report psychometric inventory / multi-item rating scale.
• Target Population: Adolescents, emerging adults, and adults evaluating specific cross-sex or same-sex friendships, or judging friendship dynamics in the abstract.
• Administration Format: Paper-and-pencil or computer-assisted survey administration. Target-specific versions adapt third-person pronouns (e.g., “he/him” vs. “she/her”) to match the gender of the focal friend.
• Item Count: 115 unique operationalized statements (as presented in the primary research instrument).
• Response Format / Scale: 7-point Likert-type continuous rating scale anchored from 1 (“Not at all”) to 4 (“Somewhat”) to 7 (“Very”). In standard research designs, respondents evaluate each item under one or both evaluative inquiries:
  • “How Beneficial?” (1 = Not at all beneficial, 4 = Somewhat beneficial, 7 = Very beneficial)
  • “How Costly?” (1 = Not at all costly, 4 = Somewhat costly, 7 = Very costly)
• Scoring and Aggregation Procedures:
  • Subscale composite scores are calculated by computing the unweighted arithmetic mean of items loading onto each respective theoretical factor.
  • Higher scores on benefit dimensions reflect greater perceived fitness utility and psychological support derived from the friendship.
  • Higher scores on cost dimensions reflect greater perceived relational burden, social friction, sexual conflict, and resource depletion.

11. Permissions & Fee and Test Year

The Costs and Benefits of Friendship scale was developed and introduced in the peer-reviewed literature in 2000 by April L. Bleske and David M. Buss, published in Personal Relationships. The instrument was developed within an academic research context and is widely accessible for non-commercial, academic, clinical, and scholarly research purposes without licensing fees, provided proper citation of the original source publication is maintained. Commercial use, reproduction in proprietary diagnostic software, or standardized corporate applications requires written permission from the copyright holders and the International Association for Relationship Research (IARR) / John Wiley & Sons.

12. References

Below are primary references and foundational literature informing the psychometric and evolutionary development of the scale:

• Bleske, A. L., & Buss, D. M. (2000). Can men and women just be friends? Personal Relationships, 7(2), 131–151. https://doi.org/10.1111/j.1475-6811.2000.tb00008.x
• Bleske-Rechek, A., Somers, E., Micke, C., Erickson, P., Matteson, L., Stocco, C., Schumacher, B., & Ritchie, L. (2012). Benefit or burden? Attraction in cross-sex friendship. Journal of Social and Personal Relationships, 29(5), 569–596. https://doi.org/10.1177/0265407512443616
• Buss, D. M. (2016). Evolutionary psychology: The new science of the mind (5th ed.). Routledge. https://doi.org/10.4324/9781315663401
• Buss, D. M., & Schmitt, D. P. (1993). Sexual Strategies Theory: An evolutionary perspective on human mating. Psychological Review, 100(2), 204–232. https://doi.org/10.1037/0033-295X.100.2.204
• Kaplan, D. L., & Keys, C. B. (1997). Sex and relationship variables as predictors of sexual attraction in cross-sex friendships. Journal of Social and Personal Relationships, 14(2), 191–206. https://doi.org/10.1177/0265407597142003
• Pfeiffer, S. M., & Wong, P. T. (1989). Multidimensional jealousy. Journal of Social and Personal Relationships, 6(2), 181–196. https://doi.org/10.1177/026540758900600203
• Simpson, J. A., & Gangestad, S. W. (1991). Individual differences in sociosexuality: Evidence for convergent and discriminant validity. Journal of Personality and Social Psychology, 60(6), 870–883. https://doi.org/10.1037/0022-3514.60.6.870
• Swain, S. (1992). Men’s friendships with women: Intimacy, emotionality, and sexual boundaries. In P. M. Nardi (Ed.), Men’s friendships (pp. 153–172). Sage Publications.
• Tooby, J., & Cosmides, L. (1996). Friendship and the Banker’s Paradox: Other pathways to the evolution of adaptations for altruism. Proceedings of the British Academy, 88, 119–143.
• Trivers, R. L. (1971). The evolution of reciprocal altruism. The Quarterly Review of Biology, 46(1), 35–57. https://doi.org/10.1086/406755
• Trivers, R. L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual selection and the descent of man, 1871-1971 (pp. 136–179). Aldine Publishing.

13. Items of the Scale