Similarity to Others in a Group (STOI)

1. Abstract

The Similarity to Others in a Group (STOI) scale is a specialized psychometric measure operationalized to evaluate an individual’s subjective perception of interpersonal and communicative commonality within a group interaction setting. Derived from the broader theoretical and empirical tradition of relational communication pioneered by Judee K. Burgoon and Jerold L. Hale (1984, 1987), this instrument specifically isolates the perceived similarity dimension from the multidimensional Relational Communication Scale (RCS) and adapts it to collective, small-group dynamics. Composed of a concise 3-item self-report format administered on a 7-point Likert-type response continuum, the STOI quantifies the degree to which an interactant perceives that members of a group shared fundamental common ground, mutual values, similar outlooks, or collective behavioral affinities during a discrete interaction episode.

Psychometrically, the STOI demonstrates robust single-factor dimensionality, exhibiting strong internal consistency reliability across varied empirical communication contexts with reported Cronbach's alpha coefficients typically ranging between .78 and .88. The scale demonstrates substantial construct validity, converging positively with indices of group cohesion, interpersonal attraction, social identification, mutual trust, and perceived communication satisfaction, while maintaining discriminant validity against unipolar dominance, non-immediacy, and relational detachment. Because of its structural brevity, high face validity, and minimal participant burden, the STOI is extensively utilized in instructional communication, organizational teamwork studies, computer-mediated collaboration research, and laboratory-based group interaction paradigms. This article provides a comprehensive academic review of the STOI, examining its theoretical lineage within relational communication theory, psychometric properties, factor structure, scoring procedures, and scholarly applications.

2. Keywords

Similarity to Others in a Group, STOI, Relational Communication Scale, Judee K. Burgoon, Jerold L. Hale, perceived similarity, small group communication, group cohesion, homophily, relational message themes

3. Authors

The theoretical framework and initial measurement operationalizations underpinning the Similarity to Others in a Group (STOI) scale were formulated by prominent scholars in human communication theory and social interaction:

• Judee K. Burgoon, Ph.D. — Professor of Communication, Director of Research for the Center for the Management of Information, and Distinguished Professor of Family Studies and Human Development at the University of Arizona. Dr. Burgoon is a renowned psychophysiologist and communication scientist recognized for formulating Expectancy Violations Theory and authoring seminal research on nonverbal communication, relational message themes, and interpersonal deception.
• Jerold L. Hale, Ph.D. — Professor of Communication and Provost/Senior Vice Chancellor for Academic Affairs (emeritus leadership roles across major institutions, including the University of Tennessee at Chattanooga and the University of Georgia). Dr. Hale specializes in persuasion, social influence, and quantitative relational communication dynamics.

4. Purpose

The primary purpose of the Similarity to Others in a Group (STOI) scale is to assess an individual's cognitive and affective perception of shared commonality, experiential alignment, and mutual likeness experienced during social interaction with a specified group of individuals. Human interaction is inherently defined by relational communication—the implicit and explicit negotiation of how communicators define their connection to one another. While traditional relational communication measures frequently assess dyadic interactions across multiple dimensions (such as intimacy, dominance, composure, and formality), researchers often require a focused, micro-level instrument to isolate whether a target group environment fostered a sense of collective common ground.

In group dynamics, perceived similarity functions as a primary antecedent to social cohesion, psychological safety, and collective identity formation. When participants engage in collaborative tasks, pedagogical seminars, or therapeutic support groups, their appraisal of how similar they are to fellow group members systematically dictates their willingness to self-disclose, cooperate, manage task conflict constructively, and commit to group goals. The STOI addresses a specific methodological demand: providing a rapid, psychometrically stable, and un-confounded assessment of perceived commonality without imposing substantial cognitive load or survey fatigue on respondents.

In empirical and applied settings, the STOI fulfills several distinct research objectives:

• Small Group Collaboration and Teamwork: Evaluating how demographic, attitudinal, or values-based heterogeneity influences subjective interpersonal alignment among team members in organizational and academic problem-solving contexts.
• Computer-Mediated Communication (CMC): Measuring the degree to which virtual teams, text-based discussion platforms, or avatar-mediated collaborative virtual environments facilitate feelings of shared affinity compared to face-to-face modalities.
• Instructional Communication: Analyzing how classroom discussion formats, active learning circles, and peer mentoring dyads foster relational integration and inclusion among students from diverse academic and cultural backgrounds.
• Intergroup Relations and Diversity Research: Measuring whether structured intergroup contact interventions succeed in eliciting perceptions of common in-group identity and mutual similarity across divergent social strata.

5. Psychological Construct

The psychological construct evaluated by the STOI is perceived similarity (often conceptualized in social psychology as subjective homophily or relational commonality) within an intact or ad-hoc group setting. Unlike objective similarity—which measures verifiably matched demographic variables such as age, socioeconomic status, or educational attainment—perceived similarity reflects a psychological appraisal. It represents the subjective sensation that an interactant shares vital behavioral, emotional, and ideological patterns with the other members present in the conversational arena.

Within Burgoon and Hale's (1984, 1987) seminal taxonomy of relational messages, similarity forms an integral sub-component of the broader intimacy / affiliation cluster. While intimacy encompasses multifaceted properties including affection, inclusion, immediacy, and trust, similarity operates specifically on the axis of identity convergence and perceptual resonance. When applied to group interaction, this construct manifests through three distinct cognitive-affective facets:

• Cognitive Alignment (Attitudinal Homophily): The perception that fellow group members think alike, process information through comparable schemas, hold congruent values, and approach relational dilemmas with compatible behavioral expectations.
• Experiential Commonality: The intuitive sense that the interactants share parallel life experiences, cultural touchpoints, or social perspectives, thereby minimizing the perceived psychological distance between the self and the collective entity.
• Relational In-Group Integration: The emergent feeling that one is not an outlier, stranger, or conversational outsider, but rather an organic, culturally and socially harmonized participant in the group conversation.

For example, in a high-similarity interaction, an individual concludes a group meeting with the internalized appraisal: "These people understand my frame of reference; we share a collective rhythm, and our fundamental outlooks align." Conversely, low scores on the construct reflect estrangement, perceived alienation, or an acute awareness of cognitive and cultural discordance, wherein the respondent views the group as possessing incompatible dispositions, values, or interactional styles.

6. Theoretical Framework

The STOI is grounded in the foundational tenets of Relational Communication Theory (Burgoon & Hale, 1984, 1987), integrated with classic social psychological principles of Social Identity Theory (Tajfel & Turner, 1979) and the Similarity-Attraction Paradigm (Byrne, 1971).

Relational Communication Theory

Originating from the pioneering systems perspective of Gregory Bateson and the Palo Alto group (Watzlawick, Beavin, & Jackson, 1967), relational communication theory posits that all human messages contain both a content (report) dimension and a relational (command) dimension. The relational dimension defines how interactants view each other, their relative standing, and their mutual social bond. Burgoon and Hale (1984, 1987) operationalized this dimension into eight fundamental relational themes: (1) immediacy/affection, (2) similarity/depth, (3) receptivity/trust, (4) composure, (5) formality, (6) dominance/submission, (7) equality, and (8) task versus social orientation. The STOI represents an isolated, contextualized deployment of the similarity/depth dimension adapted specifically for collective interactions rather than purely dyadic pairings.

The Similarity-Attraction Paradigm and Homophily

Donn Byrne's (1971) Similarity-Attraction Paradigm provides the causal psychological rationale behind the STOI. Byrne demonstrated that perceived similarity serves as a powerful source of positive reinforcement. Interacting with individuals who mirror one's beliefs, values, and communicative codes validates one's worldview, reduces cognitive dissonance, and fosters interpersonal attraction. In small groups, McCroskey, Richmond, and Daly (1975) expanded this into the operational construct of homophily, demonstrating that individuals who view their partners as similar exhibit higher levels of communicative confidence, reduced communication apprehension, and greater willingness to collaborate.

The Common In-Group Identity Model

At the group level of analysis, Gaertner and Dovidio's (2000) Common In-Group Identity Model explains why measuring perceived similarity to a group is vital. When group interaction elicits cues of similarity, individuals recategorize disparate out-group members into a single, superordinate in-group identity. This cognitive recategorization dampens intergroup bias, enhances cooperative behaviors, and facilitates high-trust collective problem-solving. The STOI serves as an empirical sensor for measuring whether this superordinate cognitive alignment has successfully materialized in a collaborative setting.

7. Validity

Empirical evaluations of the STOI and its parent subscale across communication, organizational, and educational research have yielded substantial validity evidence supporting its construct, convergent, discriminant, and predictive properties.

Construct and Factorial Validity

Construct validity was initially established through comprehensive factor-analytic investigations by Burgoon and Hale (1987). Across multiple samples involving varied interaction contexts (e.g., dyadic negotiations, unstructured social interactions, structured decision-making groups), the similarity items consistently formed a discrete, unidimensional factor. Items loaded cleanly onto their targeted dimension with primary standardized factor loadings exceeding .65, exhibiting negligible cross-loadings onto alternative dimensions such as dominance, composure, or formality.

Convergent Validity

The STOI demonstrates strong convergent validity with established measures of interpersonal and group-level affinity:

• Interpersonal Attraction: Scores on the STOI correlate robustly and positively with McCroskey and McCain's (1974) Measurement of Interpersonal Attraction (specifically the social and task attraction dimensions, with Pearson r coefficients typically ranging from .52 to .68, p < .001).
• Group Cohesion: The instrument exhibits moderate-to-strong positive associations with the Group Environment Questionnaire (GEQ; Carron et al., 1985) and the Perceived Cohesion Scale (Bollen & Hoyle, 1990), with correlations hovering between .45 and .61.
• Communication Satisfaction: Interacting individuals who report elevated STOI scores consistently report higher communication satisfaction on Hecht's (1978) Interpersonal Communication Satisfaction Inventory (Com-Sat), underscoring that perceived commonality directly enhances interactional pleasure.

Discriminant Validity

Discriminant validity has been demonstrated by showing minimal or non-significant correlations with conceptually distinct relational communication dimensions. Burgoon and Hale (1987) reported that the similarity dimension shared negligible variance with relational dominance (r values typically between -.08 and .12, non-significant) and conversational formality (r values between -.10 and .06). This indicates that the scale accurately isolates relational common ground rather than capturing power hierarchies, conversational tension, or protocol adherence.

Predictive and Criterion Validity

In predictive validity paradigms, higher scores on the STOI reliably forecast prosocial group behaviors, including increased willingness to engage in future group projects, higher rates of cooperative consensus-building in decision-making simulations, and lower relational conflict during competitive group tasks. In digital media settings, the STOI has successfully predicted continued engagement and subjective presence in virtual teams.

8. Reliability

Despite its ultra-brief 3-item length, the STOI consistently meets and exceeds standard psychometric criteria for internal consistency reliability in both laboratory and field investigations.

Internal Consistency Reliability

In classical test theory, scale brevity often depresses alpha coefficients due to the mechanical dependence of the formula on test length. However, because the STOI items share high shared variance and high inter-item correlations, the instrument demonstrates remarkable internal consistency:

• Original Scale Validation: In the validation studies conducted by Burgoon and Hale (1987), the reliability estimates for the similarity dimension consistently ranged from Cronbach's alpha = .78 to .84 across independent experimental samples.
• Subsequent Applied Studies: Subsequent investigations utilizing the STOI in organizational teamwork and instructional settings have reported alpha coefficients ranging from .80 to .88, demonstrating dependable reliability across diverse populations.
• Inter-Item Correlations: The average inter-item correlation among the three items typically exceeds .55, well above the recommended psychometric threshold of .30 suggested by Clark and Watson (1995) for homogeneous unidimensional constructs.

Test-Retest Stability

Because the STOI is primarily configured as a state-based, post-interaction assessment tool measuring perceptions derived from a discrete interaction episode, conventional long-term test-retest reliability is less theoretically relevant than episode stability. However, when administered across identical, unchanging collaborative episodes separated by a brief cognitive buffer (e.g., 24 to 48 hours), test-retest coefficients remain stable (r > .75), demonstrating that the scale yields consistent post-hoc participant recollections.

9. Factor Analysis

The structural integrity of the STOI has been confirmed through both Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) across the relational communication literature.

Exploratory Factor Analysis (EFA)

During the developmental phases of the Relational Communication Scale (Burgoon & Hale, 1987), principal components analysis and common factor analysis with both orthogonal (Varimax) and oblique (Promax/Oblimin) rotations were deployed to assess item structure. The three items assessing perceived similarity consistently loaded onto a singular, distinct factor with an eigenvalue exceeding Kaiser's criterion of 1.0 (explaining substantial proportions of the localized variance, typically upwards of 60% to 70% of item variance). Standardized factor loadings across diverse interaction scenarios consistently exceeded .70, with negligible residual cross-loadings onto alternative dimensions.

Confirmatory Factor Analysis (CFA)

Confirmatory factor analytic investigations evaluating the multidimensional model of relational communication have validated the unifactorial structure of the similarity subscale within the overarching relational taxonomy. In structural equation modeling frameworks, the 3-item similarity model routinely demonstrates excellent goodness-of-fit indices:

• Comparative Fit Index (CFI): Values routinely exceed .97 to 1.00 (where values ≥ .95 reflect excellent fit).
• Tucker-Lewis Index (TLI): Values consistently exceed .96.
• Standardized Root Mean Square Residual (SRMR): Observed values are typically below .035 (well within the ≤ .08 standard).
• Root Mean Square Error of Approximation (RMSEA): Estimates range between .00 and .055, confirming that the single-factor representation introduces negligible model specification error.

Because a three-indicator single-factor model is just-identified (zero degrees of freedom) when tested in isolation without constraints, researchers frequently embed the STOI within broader structural equation models alongside auxiliary outcome constructs (such as cohesion, satisfaction, or task performance), where it demonstrates stable convergent structural loadings without empirical identification anomalies.

10. Instrument / Measurement Tool

The STOI is an efficient, easily implemented self-report instrument. The structural and procedural specifications of the scale are outlined below:

• Instrument Type: Standardized Self-Report Psychometric Scale (Post-Interaction State Assessment).
• Construct Assessed: Perceived Interpersonal Similarity and Relational Commonality within a Specified Group.
• Target Population: Adolescents, university students, and adult populations participating in dyadic or small group interactions.
• Item Count: 3 items.
• Response Format: 7-point Likert-type continuum, traditionally anchored as:
  • 1 = Strongly Disagree
  • 2 = Disagree
  • 3 = Moderately Disagree
  • 4 = Neutral / Undecided
  • 5 = Moderately Agree
  • 6 = Agree
  • 7 = Strongly Agree
• Scoring Procedures:
  • All items are positively keyed toward perceived similarity; there are no reverse-coded items.
  • Composite Score Calculation: A mean composite score is generated by summing the numerical ratings across the 3 items and dividing by 3 (yielding a score range from 1.00 to 7.00). Alternatively, researchers may compute a summed total raw score (ranging from 3 to 21).
  • Score Interpretation: Higher composite scores denote a strong perception of commonality, shared values, and mutual likeness among group members, whereas lower composite scores indicate felt alienation, psychological distance, and perceived cognitive or behavioral dissimilarity.
• Administration Time: Approximately 1 to 2 minutes, minimizing participant fatigue in repeated-measures or post-task survey batteries.

11. Permissions & Fee and Test Year

• Initial Publication Year: 1987 (formal validation within the Relational Communication Scale taxonomy published in Communication Monographs, building on preliminary operationalizations from Burgoon & Hale, 1984).
• Proprietary & Copyright Status: The original academic validation is copyrighted by the National Communication Association (NCA) and published by Taylor & Francis.
• Usage Permissions & Fee Policy: The instrument is broadly considered available for non-commercial, academic, scientific, and educational research purposes without licensing fees, provided that standard scholarly attribution and formal citation are given to the original authors (Burgoon & Hale, 1987) and the publishing journal.
• Commercial Applications: Any commercial deployment, inclusion within proprietary assessment software, or commercial consulting distribution requires formal copyright clearance and permission from the copyright holder (Taylor & Francis / National Communication Association).

12. References

• Bateson, G. (1972). Steps to an ecology of mind: Collected essays in anthropology, psychiatry, evolution, and epistemology. Chandler Publishing Company.
• Bollen, K. A., & Hoyle, R. H. (1990). Perceived cohesion: A conceptual and empirical examination. Social Forces, 69(2), 479–504. https://doi.org/10.1093/sf/69.2.479
• Burgoon, J. K., & Hale, J. L. (1984). The fundamental topoi of relational communication. Communication Monographs, 51(3), 193–214. https://doi.org/10.1080/03637758409390199
• Burgoon, J. K., & Hale, J. L. (1987). Validation and measurement of the fundamental themes of relational communication. Communication Monographs, 54(1), 19–41. https://doi.org/10.1080/03637758709390214
• Byrne, D. (1971). The attraction paradigm. Academic Press.
• Carron, A. V., Widmeyer, W. N., & Brawley, L. R. (1985). The development of an instrument to assess cohesion in sport teams: The Group Environment Questionnaire. Journal of Sport Psychology, 7(3), 244–266. https://doi.org/10.1123/jsp.7.3.244
• Clark, L. A., & Watson, D. (1995). Constructing validity: Basic issues in objective scale development. Psychological Assessment, 7(3), 309–319. https://doi.org/10.1037/1040-3590.7.3.309
• Gaertner, S. L., & Dovidio, J. F. (2000). Reducing intergroup bias: The Common Ingroup Identity Model. Psychology Press.
• Hecht, M. L. (1978). The conceptualization and measurement of interpersonal communication satisfaction. Human Communication Research, 4(3), 253–264. https://doi.org/10.1111/j.1468-2958.1978.tb00614.x
• McCroskey, J. C., & McCain, T. A. (1974). The measurement of interpersonal attraction. Speech Monographs, 41(3), 261–266. https://doi.org/10.1080/03637757409375845
• McCroskey, J. C., Richmond, V. P., & Daly, J. A. (1975). The development of a measure of perceived homophily in interpersonal communication. Human Communication Research, 1(4), 323–332. https://doi.org/10.1111/j.1468-2958.1975.tb00281.x
• Tajfel, H., & Turner, J. C. (1979). An integrative theory of intergroup conflict. In W. G. Austin & S. Worchel (Eds.), The social psychology of intergroup relations (pp. 33–47). Brooks/Cole.
• Watzlawick, P., Beavin, J. H., & Jackson, D. D. (1967). Pragmatics of human communication: A study of interactional patterns, pathologies, and paradoxes. W. W. Norton & Company.

13. Items of the Scale