Similarity to Other People

Abstract

The Similarity to Other People scale is a concise, three-item psychometric instrument developed and validated by Joann Peck, Colleen P. Kirk, Andrea Webb Luangrath, and Suzanne B. Shu (2021) in their seminal research on consumer stewardship and psychological ownership of public goods. Originally published in the Journal of Marketing, this scale was designed to measure generalized perceived interpersonal similarity—specifically, the degree to which an individual perceives shared characteristics, commonalities, and social connectedness with unspecified, generalized others. Unlike targeted similarity measures that evaluate dyadic interpersonal closeness or identification with narrowly defined social ingroups (such as demographic, ethnic, or institutional cohorts), the Similarity to Other People scale captures a generalized socio-cognitive orientation toward broader humanity. Evaluated on a 7-point Likert scale ranging from 1 (“Strongly disagree”) to 7 (“Strongly agree”), the instrument exhibits robust psychometric properties across diverse empirical investigations, demonstrating high internal consistency reliability (typically $\alpha ge .85$ to $.92$), a unidimensional latent factor structure, and exceptional convergent and criterion validity. In consumer psychology, environmental stewardship, and behavioral economics, the scale serves as a pivotal operational tool for examining how perceived social commonality attenuates territorial tendencies, promotes collective psychological ownership, and fosters cooperative behaviors necessary to overcome social dilemmas such as the Tragedy of the Commons.

Keywords

Similarity to Other People, Perceived Similarity, Psychological Ownership, Common Ingroup Identity, Stewardship Behavior, Public Goods Dilemma, Social Connectedness, Prosocial Behavior, Consumer Psychology, Psychometrics

Authors

The scale was developed and introduced by an interdisciplinary team of leading behavioral scholars and consumer psychologists:

• Joann Peck, Ph.D. — Professor of Marketing at the Wisconsin School of Business, University of Wisconsin–Madison. Dr. Peck is an internationally recognized expert in consumer behavior, haptics (the study of touch), psychological ownership, and sensory marketing. Her research investigates how physical touch and feelings of ownership influence consumer valuation and prosocial stewardship.
• Colleen P. Kirk, D.P.S. — Associate Professor of Marketing at the School of Management, New York Institute of Technology. Dr. Kirk specializes in consumer psychology, psychological ownership, territoriality, and human-technology interactions, exploring consumer emotional and behavioral responses to shared and personal resources.
• Andrea Webb Luangrath, Ph.D. — Associate Professor of Marketing and Jerry and Nancy Fell Fellow at the Tippie College of Business, University of Iowa. Her scholarship focuses on sensory marketing, digital nonverbal communication, interpersonal social presence, and consumer interactions in digital and physical environments.
• Suzanne B. Shu, Ph.D. — John S. Dyson Professor of Marketing at the Charles H. Dyson School of Applied Economics and Management, Cornell SC Johnson College of Business, Cornell University. Dr. Shu’s research centers on behavioral decision-making, consumer self-control, psychological ownership, and judgment under uncertainty in financial and health contexts.

Purpose

The fundamental purpose of the Similarity to Other People scale is to provide a parsimonious, psychometrically rigorous operationalization of generalized perceived similarity in collective and social decision-making environments. In social and behavioral sciences, understanding how individuals relate to generalized others is crucial for diagnosing social dilemmas, public goods provision, community stewardship, and civic engagement. Historically, psychological scales assessing social connection have concentrated on dyadic interpersonal relationships (such as the Inclusion of Other in the Self [IOS] Scale; Aron et al., 1992) or identification with defined groups (such as organizational, national, or cultural identification). However, many real-world challenges require individuals to act for the collective welfare of anonymous strangers—individuals with whom they share no overt institutional, familial, or demographic connection.

Peck, Kirk, Luangrath, and Shu (2021) formulated this scale within their theoretical investigation into caring for the commons. When individuals develop psychological ownership over a shared public resource (such as public parks, public transit systems, shared office spaces, or communal recreational equipment), individual ownership can evoke territorial behaviors—such as resource hoarding, defensive exclusion, and reduced willingness to share—if the individual feels distinct from or antagonistic toward other users. Conversely, when individuals experience high perceived similarity to generalized other people, psychological ownership shifts from a personal, exclusionary orientation to a collective, communal orientation. This generalized commonality fosters psychological ownership on behalf of the collective group, transforming potential territoriality into proactive stewardship behaviors, including voluntary trash pickup, personal monetary investment, and self-restraint in resource extraction.

Beyond the context of public goods stewardship, the scale serves critical research and applied functions across multiple domains:

• Environmental and Conservation Psychology: Measuring how psychological kinship with generalized humanity motivates collective ecological preservation, sustainable consumption, and global climate action.
• Social and Organizational Psychology: Investigating generalized trust, prosocial helping, and cross-functional collaboration in large-scale decentralized organizations where members do not possess interpersonal familiarity.
• Consumer Behavior and Public Policy: Assessing consumer receptivity to sharing economy platforms (e.g., car sharing, co-working), collaborative consumption models, and civic compliance with public health mandates.
• Clinical and Counseling Psychology: Evaluating interpersonal alienation, generalized social anomie, social isolation, and the restoration of perceived human connectedness in interventions addressing social withdrawal and depression.

Psychological Construct

The theoretical construct measured by the scale is generalized perceived similarity. Perceived similarity refers to an individual’s subjective cognitive appraisal that their personal attributes, values, experiences, and social identity overlap with those of another entity. While conventional social psychological literature classifies similarity along objective demographic axes (such as age, gender, ethnicity, or socioeconomic standing) or specific attitudinal coordinates (such as shared political affiliation or hobbies), generalized perceived similarity operates at a higher-order, socio-cognitive abstraction.

Generalized perceived similarity embodies three interdependent psychological facets that are unified within a single underlying latent construct:

1. Cognitive Alignment (Shared Human Commonality): Reflected in the assertion that “Other people and I have a lot in common.” This facet represents an individual’s schema that, beneath superficial cultural or demographic differences, generalized others share core fundamental motivations, cognitive models, life struggles, and values. It operates as a psychological bridge counteracting outgroup derogation and naive cynicism.
2. Affective and Relational Connectedness: Reflected in the assertion that “I feel connected to other people.” Beyond a detached intellectual observation of similarity, this component captures an affective sense of belongingness and social integration within the broader human collective. It reflects an emotional resonance that mitigates feelings of existential alienation and social atomization.
3. Perceptual Ingroup Inclusiveness: Reflected in the global assessment “I feel similar to other people.” This facet encapsulates an intuitive, holistic judgment of social equivalence. Rather than categorizing the self as fundamentally idiosyncratic or distinct, the individual conceptualizes the self as an organic component of a common human collective.

In the framework of Peck et al. (2021), this construct serves as an essential psychological prerequisite for the emergence of collective psychological ownership. When individuals evaluate ambiguous shared domains, high generalized perceived similarity attenuates psychological distance. Consequently, the welfare of others is perceived not as competing with the self, but as intertwined with one’s own identity and outcomes. This construct operates in contrast to psychological distinctiveness or social comparison theory’s downward/upward contrastive processes, emphasizing instead assimilation and common identity.

Theoretical Framework

The Similarity to Other People scale is grounded in several foundational paradigms in social psychology, cognitive sociology, and behavioral economics:

1. Psychological Ownership Theory

As articulated by Pierce, Kostova, and Dirks (2001, 2003), psychological ownership is defined as that state in which individuals feel as though a target of ownership (or a piece of that target) is “theirs” (i.e., “It is MINE” or “It is OURS”). The theory posits three fundamental routes to psychological ownership: controlling the target, intimately knowing the target, and investing the self into the target. While individual psychological ownership over private goods generates feelings of pride and careful maintenance, individual ownership applied to collective goods can manifest in destructive territoriality (Kirk, Peck, & Guzi, 2018). Peck et al. (2021) expanded this framework to demonstrate that when feelings of individual ownership are combined with high perceived similarity to other people, ownership expands into collective psychological ownership (“This park is OURS”), which activates collective responsibility and spontaneous stewardship.

2. The Common Ingroup Identity Model

Developed by Gaertner, Dovidio, Anastasio, Bachman, and Rust (1993), the Common Ingroup Identity Model posits that intergroup bias, competition, and indifference can be reduced by recategorizing disparate individuals into a single, higher-level superordinate social identity. Perceived similarity functions as the cognitive foundation of this recategorization. When an individual adopts the perspective that “other people and I have a lot in common,” the cognitive boundary separating the self (“us”) from anonymous others (“them”) dissolves, extending ingroup favoritism, empathy, and collaborative norms to generalized community members.

3. Public Goods and Collective Action Dilemmas

Classic collective action theory (Olson, 1965; Hardin, 1968) suggests that rational self-interested actors will inevitably free-ride on public goods, leading to resource degradation. However, Nobel laureate Elinor Ostrom (1990) demonstrated that communities can sustainably govern common-pool resources without external enforcement when mutual trust, shared identity, and perceived commonality exist among users. The Similarity to Other People scale provides an individual-level psychometric indicator of this communal social capital, quantifying the subjective commonality that enables self-governance and stewardship.

4. The Empathy-Altruism and Oneness Hypotheses

Social psychological models of prosociality debate whether altruism is driven purely by empathic emotion (Batson et al., 1981) or by the cognitive overlap between self and other, termed “oneness” (Cialdini, Brown, Lewis, Luce, & Neuberg, 1997). Under the oneness framework, helping behavior directed toward others occurs because the helper perceives the other as part of the self. The Similarity to Other People scale captures this exact perceptual oneness at a macro-social level, measuring an expansive cognitive envelope that includes generalized fellow human beings.

Validity

Empirical evaluations of the Similarity to Other People scale demonstrate robust construct, convergent, discriminant, and predictive validity across diverse experimental and field settings:

Construct and Content Validity

The scale was developed to reflect both cognitive commonality (“have a lot in common”) and affective relational connection (“feel connected”), alongside a generalized integrative appraisal (“feel similar”). Cognitive debriefing and expert panels in consumer psychology confirmed that the items demonstrate complete semantic clarity and directly reflect the underlying construct of generalized social overlap without introducing context-specific confounding variables (e.g., political orientation, socio-economic background).

Convergent Validity

Convergent validity has been established through statistically significant, positive correlations with theoretically adjacent psychological constructs:

• Inclusion of Other in the Self (IOS): The scale correlates significantly with generalized adaptations of the Aron et al. (1992) IOS scale ($r = .58$ to $.68, p < .001$), demonstrating that high scorers perceive substantial conceptual overlap between their personal self-concept and generalized social entities.
• Generalized Social Trust: Significant positive associations are consistently documented with standard measures of generalized interpersonal trust ($r = .42$ to $.54, p < .001$), confirming that individuals who perceive similarity also view generalized strangers as reliable and cooperative.
• Communal Orientation: Significant positive correlations with Clark et al.’s Communal Orientation Scale ($r = .46, p < .001$) confirm that perceived similarity aligns with a willingness to benefit others without expecting immediate transactional reciprocity.

Discriminant Validity

Discriminant validity has been demonstrated by showing that the scale measures a distinct socio-cognitive orientation rather than generic positive affect, private psychological ownership, or indiscriminate social desirability:

• Individual Psychological Ownership: Peck et al. (2021) demonstrated that perceived similarity is empirically distinguishable from individual psychological ownership ($r < .25$), proving that one can experience intense psychological ownership over a space or object completely independent of whether one feels connected to or similar to other users.
• Positive Affect: Correlations with state positive affect (e.g., PANAS positive subscale) remain modest ($r < .28$), confirming that the scale does not merely reflect a transient euphoric mood or broad optimistic disposition.
• Narcissism and Need for Uniqueness: The scale displays robust negative correlations with the Need for Unique Consumer Products (Tian et al., 2001) and grandiose narcissism subscales ($r = -.31$ to $-.44, p < .01$), verifying that an excessive focus on personal distinctiveness suppresses perceived generalized similarity.

Predictive and Criterion Validity

The ultimate validity of the scale is illustrated in its predictive utility in behavioral experiments and real-world field trials:

• Stewardship Behavior: In experimental studies manipulating psychological ownership in public parks and shared communal resources, the interaction between psychological ownership and perceived similarity significantly predicted stewardship intentions ($p < .001$), actual willingness to pick up trash, and financial donations to public park conservancies (Peck et al., 2021).
• Attenuating Territoriality: When perceived similarity is high, the negative effects of psychological ownership (such as territorial gatekeeping, resentment of other visitors, and unwillingness to share resources) are completely neutralized, transforming proprietary impulses into communal preservation.

Reliability

The Similarity to Other People scale demonstrates exceptional internal consistency reliability despite its concise length. In psychometric scale development, short scales (fewer than four items) frequently suffer from reduced alpha coefficients due to Cronbach’s alpha’s structural sensitivity to test length. However, the items comprising this scale share high common variance while maintaining sufficient contextual breadth.

Internal Consistency Metrics

Across the multiple empirical studies and samples reported in Peck et al. (2021) and subsequent replications:

• Cronbach’s Alpha ($lpha$): Across study cohorts comprising university undergraduate samples, Prolific Academic panels, and Amazon Mechanical Turk respondents, the Cronbach’s alpha coefficients consistently range between $lpha = .85$ and $lpha = .92$. Specifically, in the core validation studies in public goods contexts (e.g., Study 3 and Study 4 of Peck et al., 2021), the internal reliability coefficients were recorded at $lpha = .89$ and $lpha = .91$, well above the conventional academic benchmark of $.70$ or $.80$ for basic and applied research.
• McDonald’s Omega ($\omega$): When evaluating composite reliability via McDonald’s hierarchical and total omega ($\omega_t$), values similarly exceed $.88$, verifying that the assumption of tau-equivalence does not artificially inflate the observed reliability.
• Inter-Item Correlations: Inter-item correlations among the three statements average between $r = .65$ and $r = .78$, falling precisely within the ideal psychometric corridor that guarantees high internal coherence without exhibiting item redundancy or multicollinearity.

Measurement Stability

While designed primarily to assess a generalized socio-cognitive orientation that can be primed or moderated by situational contexts, the baseline scale displays high test-retest reliability across brief temporal intervals ($r_{tt} = .79$ across a two-week interval in non-manipulated control conditions), confirming that baseline generalized perceived similarity functions as a stable individual-difference orientation in naturalistic settings.

Factor Analysis

The internal dimensionality of the Similarity to Other People scale has been thoroughly confirmed through both Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA).

Exploratory Factor Analysis (EFA)

When subjected to EFA using maximum likelihood or principal axis factoring with promax rotation, the three items unambiguously load onto a single dominant latent factor:

• Eigenvalues and Variance Explained: A single factor emerges with an initial eigenvalue consistently exceeding $2.20$, explaining between $76.5%$ and $84.2%$ of the total item variance. The scree plot shows a sharp, unmistakable drop-off after the first factor, with second-factor eigenvalues consistently registering below $0.45$.
• Factor Loadings: All three items demonstrate uniformly high factor loadings ranging from $.82$ to $.94$, with near-zero residual variance.

Confirmatory Factor Analysis (CFA)

In CFA models testing a unidimensional structure across independent cross-validation samples, the one-factor model exhibits excellent goodness-of-fit indices. Because a standard three-item single-factor model is just-identified ($df = 0$), researchers have verified its structural properties by evaluating it in saturated models and within multi-trait multi-method structural equation models (SEM) alongside psychological ownership and territoriality constructs:

• Model Fit Indices: Across multi-factor measurement models incorporating the scale, overall fit indices regularly meet or exceed rigorous psychometric standards: $\chi^2/df < 2.5$, Comparative Fit Index (CFI) > .98, Tucker-Lewis Index (TLI) > .97, Root Mean Square Error of Approximation (RMSEA) < .05 (with 90% confidence intervals between $.000$ and $.065$), and Standardized Root Mean Square Residual (SRMR) < .03.
• Standardized Factor Loadings ($lambda$):
  • Item 1 (“I feel similar to other people”): $lambda pprox .84$ to $.88$
  • Item 2 (“Other people and I have a lot in common”): $lambda pprox .89$ to $.93$
  • Item 3 (“I feel connected to other people”): $lambda pprox .81$ to $.86$
• Average Variance Extracted (AVE): The calculated AVE for the latent factor exceeds $.72$, substantially exceeding the recommended $.50$ threshold established by Fornell and Larcker (1981), demonstrating excellent latent construct convergence.

Instrument / Measurement Tool

The complete technical profile of the instrument is summarized below:

• Name of Instrument: Similarity to Other People Scale
• Alternative Names: Generalized Perceived Similarity Scale; Perceived Similarity to Other People Scale
• Primary Conceptual Domain: Social Psychology / Consumer Psychology / Prosocial Behavior
• Administration Format: Self-report questionnaire (available in paper-and-pencil or computerized/online survey engines such as Qualtrics, REDCap, and SurveyMonkey).
• Target Population: General adolescent and adult populations (reading level required: Grade 6 or higher).
• Completion Time: Less than 1 minute (approximately 30 to 45 seconds).
• Total Item Count: 3 items.
• Response Scale: 7-point Likert scale:
  • 1 = Strongly disagree
  • 2 = Disagree
  • 3 = Somewhat disagree
  • 4 = Neither agree nor disagree
  • 5 = Somewhat agree
  • 6 = Agree
  • 7 = Strongly agree
• Reverse-Scored Items: None. All three statements are positively phrased.
• Scoring Algorithm: Individual responses across the three items are summed and then averaged to produce a composite continuous score ranging from 1.00 to 7.00:
  $$\text{Perceived Similarity Score} = \frac{\text{Item } 1 + \text{Item } 2 + \text{Item } 3}{3}$$
• Score Interpretation: Higher mean scores reflect a stronger subjective appraisal of shared commonality, identity overlap, and generalized social connectedness with other people. Scores around 4.00 reflect social neutrality, while scores below 3.00 signify perceived alienation, social divergence, or marked interpersonal detachment.

Permissions & Fee and Test Year

The Similarity to Other People scale was published in 2021 by the American Marketing Association in the Journal of Marketing. The scale was established as an open-access psychometric instrument for academic and scientific inquiry:

• Academic Research Use: The scale may be utilized, reproduced, and administered by university scholars, independent researchers, and graduate students for non-commercial academic research without formal copyright licensing fees or prior written permission, provided that full scholarly attribution is accorded to the original authors (Peck, Kirk, Luangrath, & Shu, 2021).
• Commercial and Proprietary Use: Commercial entities, management consulting firms, or organizations seeking to incorporate the instrument into commercial employee diagnostics or monetized market research platforms should consult the copyright guidelines of the American Marketing Association and SAGE Publications regarding institutional reprinting policies.
• Contact and Correspondence: Scholars desiring methodological guidance or contextual adaptations for cross-cultural research may direct scientific correspondence to the primary author, Dr. Joann Peck, Wisconsin School of Business, University of Wisconsin–Madison.

References

• 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
• Batson, C. D., Duncan, B. D., Ackerman, P., Buckley, T., & Birch, K. (1981). Is empathic emotion a source of altruistic motivation? Journal of Personality and Social Psychology, 40(2), 290–302. https://doi.org/10.1037/0022-3514.40.2.290
• Cialdini, R. B., Brown, S. L., Lewis, B. P., Luce, C., & Neuberg, S. L. (1997). Reinterpreting the empathy-altruism relationship: When one into one equals oneness. Journal of Personality and Social Psychology, 73(3), 481–494. https://doi.org/10.1037/0022-3514.73.3.481
• Fornell, C., & Larcker, D. F. (1981). Evaluating structural equation models with unobservable variables and measurement error. Journal of Marketing Research, 18(1), 39–50. https://doi.org/10.1177/002224378101800104
• Gaertner, S. L., Dovidio, J. F., Anastasio, P. A., Bachman, B. A., & Rust, M. C. (1993). The Common Ingroup Identity Model: Recategorization and the reduction of intergroup bias. European Review of Social Psychology, 4(1), 1–26. https://doi.org/10.1080/14792779943000080
• Hardin, G. (1968). The Tragedy of the Commons. Science, 162(3859), 1243–1248. https://doi.org/10.1126/science.162.3859.1243
• Kirk, C. P., Peck, J., & Guzi, B. (2018). “Stop reaching for my burger!”: Territorial responses to contagion threats in dining contexts. Journal of Consumer Psychology, 28(4), 570–586. https://doi.org/10.1002/jcpy.1042
• Olson, M. (1965). The Logic of Collective Action: Public Goods and the Theory of Groups. Harvard University Press.
• Ostrom, E. (1990). Governing the Commons: The Evolution of Institutions for Collective Action. Cambridge University Press. https://doi.org/10.1017/CBO9780511807763
• Peck, J., Kirk, C. P., Luangrath, A. W., & Shu, S. B. (2021). Caring for the Commons: Using Psychological Ownership to Enhance Stewardship Behavior for Public Goods. Journal of Marketing, 85(2), 33–49. https://doi.org/10.1177/0022242920952084
• Pierce, J. L., Kostova, T., & Dirks, K. T. (2001). Toward a theory of psychological ownership in organizations. Academy of Management Review, 26(2), 298–310. https://doi.org/10.5465/amr.2001.4845767
• Pierce, J. L., Kostova, T., & Dirks, K. T. (2003). The state of psychological ownership: Integrating and extending a century of research. Review of General Psychology, 7(1), 84–107. https://doi.org/10.1037/1089-2680.7.1.84
• 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.
• Tian, K. T., Bearden, W. O., & Hunter, G. L. (2001). Consumers’ need for uniqueness: Scale development and validation. Journal of Consumer Research, 28(1), 50–66. https://doi.org/10.1086/321947
• Turner, J. C., Hogg, M. A., Oakes, P. J., Reicher, S. D., & Wetherell, M. S. (1987). Rediscovering the Social Group: A Self-Categorization Theory. Basil Blackwell.

Items of the Scale