Measuring the Closeness of Relationships: A Comprehensive Evaluation of the 'Inclusion of the Other in the Self' Scale

PLoS One. 2015 Jun 12;10(6):e0129478. doi: 10.1371/journal.pone.0129478. eCollection 2015.


Understanding the nature and influence of social relationships is of increasing interest to behavioral economists, and behavioral scientists more generally. In turn, this creates a need for tractable, and reliable, tools for measuring fundamental aspects of social relationships. We provide a comprehensive evaluation of the 'Inclusion of the Other in the Self' (IOS) Scale, a handy pictorial tool for measuring the subjectively perceived closeness of a relationship. The tool is highly portable, very easy for subjects to understand and takes less than 1 minute to administer. Across our three online studies with a diverse adult population (n = 772) we show that six different scales designed to measure relationship closeness are all highly significantly positively correlated with the IOS Scale. We then conduct a Principal Component Analysis to construct an Index of Relationship Closeness and find that it correlates very strongly (ρ = 85) with the IOS Scale. We conclude that the IOS Scale is a psychologically meaningful and highly reliable measure of the subjective closeness of relationships.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Economics, Behavioral
  • Ego*
  • Female
  • Humans
  • Interpersonal Relations*
  • Male

Grant support

Funding was received from the European Research Council ( Advanced Investigator Grant COOPERATION 295707 and the UK Economic and Social Research Coincil ( grant ES/K002201/1 (Network for Integrated Behavioural Science). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.