"Where are We?": Developing Behavioral Indicators of Relationship Development (BIRD) for Quantifying Relationship Progression.

Authors

Simon Klopstad, Mons Bendixen, Leif Edward Ottesen Kennair

Published in

Evolutionary psychology : an international journal of evolutionary approaches to psychology and behavior. Volume 24. Issue 4. Pages 14747049261496263. Epub Oct 09, 2026.

Abstract

Research on romantic and sexual relationships has largely focused on short- and long-term relationships, and how they differ in terms of mating strategies and commitment. However, romantic relationships exist along a continuum. Simultaneously, intermediate relationships, such as situationships, are increasing in prevalence among young adults, characterized by romantic connection and sexual involvement without clear labeling and commitment. Current measures of love, such as Sternberg's Triangular Love Scale, rely on subjective evaluation, representing a challenge in objectively and precisely positioning individuals on this continuum or capturing the ambiguity inherent in intermediate relationships. To address this gap, we developed a behavior-based measure of relationship development using an act nomination procedure followed by a principal components analysis in a sample of 662 students in Norway. The resulting 12-item Behavioral Indicators of Relationship Development (BIRD) showed good reliability across men and women reporting on both previous and current relationships. BIRD was highly convergent with the Triangular Love Scale, was associated with sociosexuality and narcissism, and successfully differentiated between self-denoted relationship types along the short-, intermediate-, and long-term continuum. The findings suggest that relationship progression can be captured through observable behavior. This offers a complement to more subjective and emotional measures of relationship quality and assessment of past relationship development.

PMID:
42852852
Bibliographic data and abstract were imported from PubMed on 09 Oct 2026.

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