Study Finds Romantic Partners Tend to Overestimate How Similar They Are

Long-term romantic partners are most alike in honesty and openness to experience, according to the study Self/spouse agreement, similarity, and assumed similarity in the HEXACO personality factors, published in the Journal of Research in Personality. Conducted by Kibeom Lee, Michael C. Ashton, and Reinout E. de Vries, the research found that couples in lasting relationships are generally accurate when assessing each other’s personalities, although they also tend to assume they are more similar than they actually are.

To examine personality within romantic relationships, researchers used the HEXACO personality model, which groups personality into six major dimensions: Honesty-Humility, Emotionality, Extraversion, Agreeableness, Conscientiousness, and Openness to Experience.

Each of these dimensions is divided into more specific traits. For example, Honesty-Humility includes qualities such as sincerity, fairness, and modesty, while Openness to Experience encompasses curiosity, creativity, appreciation of art and beauty, and willingness to consider unconventional ideas. Together, these traits reflect important aspects of a person's values and outlook.

How the Study Was Conducted

The researchers recruited 451 heterosexual married or cohabiting couples in the Netherlands through a certified online survey panel. A total of 902 people participated, with an average age of about 55 years, providing a sample of mature, long-term relationships.

Participants had been together anywhere from one year to just over 64 years, with an average relationship length of 28 years. This allowed the researchers to examine personality similarity and perception across relationships of varying duration.

Each participant completed the 100-item HEXACO questionnaire twice. First, they evaluated their own personality using a five-point scale. They then completed the same questionnaire again, this time rating their partner's personality.

Measuring Agreement and Similarity

The researchers focused on three related concepts: self-partner agreement, actual similarity, and assumed similarity.

Self-partner agreement refers to how closely one person's ratings of their partner match that partner's own self-assessment, providing a measure of how accurately spouses understand each other's personalities.

Actual similarity reflects whether partners genuinely share similar personality traits based on their own self-reports. Assumed similarity describes the tendency to believe a partner is similar to oneself, regardless of whether that similarity actually exists.

Across all six HEXACO dimensions, self-partner agreement was high, with an average correlation of about 0.70. The findings indicate that spouses in long-term relationships generally judge each other's personalities with considerable accuracy.

Agreement was strongest for Openness to Experience, particularly for facets such as inquisitiveness and appreciation of art and beauty. The researchers noted that these scores may be close to the upper limit that can be detected using standard personality questionnaires.

Honesty-Humility showed the lowest level of self-partner agreement, although the results remained substantial. Partners were more consistent in judging observable traits such as fairness and greed avoidance than characteristics like sincerity and modesty, which are less visible in everyday behavior.

Where Couples Are Most Similar

When the researchers examined actual personality similarity, the strongest resemblance appeared in Honesty-Humility and Openness to Experience. This suggests that shared values and similar worldviews may play an important role in the formation and maintenance of long-term relationships.

People who rated themselves highly on honesty or openness were more likely to have partners who also scored highly in those same personality dimensions. By contrast, the remaining four major HEXACO traits showed little or no meaningful similarity between spouses, even after many years together.

For example, highly extroverted individuals were no more likely to be paired with another extrovert than with an introvert. Only a small number of extraversion facets, including social self-esteem and liveliness, showed modest similarity within couples.

Assumed similarity, however, was consistently stronger than actual similarity. Partners were especially likely to believe they resembled each other in Honesty-Humility and Openness to Experience, sometimes to a greater extent than their self-reports supported, suggesting a tendency to project their own values onto their spouse.

Lead author Kibeom Lee of the University of Calgary noted that traits such as modesty and sincerity can be difficult for individuals to evaluate accurately in themselves, making these characteristics harder for partners to assess as well.

What the Findings Suggest

The results support the idea that shared values, particularly those related to honesty and openness, may contribute to the development and stability of long-term relationships. According to Lee, these personality dimensions reflect fundamental ways of thinking that can influence everyday behavior as well as important life decisions.

At the same time, the researchers emphasize that the similarities observed were modest rather than universal. Many successful couples continue to maintain satisfying relationships despite noticeable differences in personality, including emotionality and extraversion.

The findings also suggest that partners do not necessarily become alike across every aspect of personality over time. Instead, some characteristics appear to be shared from the beginning of the relationship, while others remain distinct even after decades together.

The researchers also note that cultural factors may influence the results. Because all participants lived in the Netherlands, the findings may not fully apply to societies with different traditions surrounding relationships, marriage, or partner selection.

Earlier research conducted in mainland China, for example, found little or no similarity between romantic partners across HEXACO personality traits, including Honesty-Humility and Openness to Experience. It remains uncertain whether these differences reflect cultural influences, methodological factors, or both.

Future studies involving couples from a wider range of countries may help determine whether the patterns observed in the Dutch sample are consistent across cultures. Researchers also plan to explore why certain personality facets, such as social self-esteem, show modest similarity between partners.

Article prepared by Victoria Caldwell.