The idea behind our couple test is that like attracts like, not opposites. This assumption is supported by previous research in this area. For example, Bahns, Crandall, Gillath, and Preacher (2017) showed that people pay particular attention to similarities early in a partnership, during the getting-to-know-you phase. Personality also seems to be an important factor in a relationship. Gonzaga, Carter, and Galen Buckwalter (2010) found in their study that the personality similarity or. Personality congruence among the factors studied best predicts marital satisfaction. Even when we are asked to describe our ideal partner, his or her personality is usually similar to ours (Buston& Emlen, 2003). With our couple test, we want to try to replicate the previous results as well as create a measure of what level of couple similarity is optimal for a relationship. Thanks to previous studies, it can be concluded that test results greater than 0.25 indicate a good personality fit of a couple.

Summary
Results of different studies indicate that personality similarity is stronger in couples than in noncouples. This similarity does not just develop, but already exists even before the future partners get to know each other. So the personality of the partners remains uninfluenced by the partnership. Couples show personality similarity in the dimensions of "openness to experience", "Conscientiousness" and "tolerance of ca. r= 0,3. So the personalities agree within these dimensions ca. 10 percent (r²); agree. For particularly successful couples (relationship duration longer ca. 40 years) the similarity is even higher with r= 0.39, which corresponds to a personality match of ca. 16 percent (r²) corresponds to. There is always a particularly high degree of similarity between couples in the dimension "openness to experience". Satisfaction in a partnership is also influenced by personality. 10 percent is dependent on a couple’s personality similarity. If your couple test score is close to 0.3, your personality will not get in the way of your partnership plans!
Background on mating research
There are numerous studies that show that similar appearance and similar demographic characteristics (age, education, ancestry) are important factors in the search for a partner (Gonzaga et al., 2010). Personality also plays an important role. That is, whether couples with particularly high personality similarity, also referred to as personality congruence, stay together for a particularly long time and have a particularly high relationship satisfaction.
Personality similarity in couples
The study by Rammstedt and Schupp (2008) deals with the question of whether couples are similar in the Big Five personality dimensions. For this, they were able to draw on a sample of 6904 subjects who participated in the SOEP study. The SOEP study is a so-called panel study. This means that the same people are interviewed every year if possible. In 2005, among other things, the Big Five were measured by the BFI test. The BFI was also used to validate the IPIP-D-120 on deineTests. In this study, medium-strong correlations were found on average in the personality dimensions "Agreeableness" and "Tolerance" (r= 0.25) "Conscientiousness" (r= 0.31) and "openness to experience" (r= 0,33). In the dimensions neuroticism (r= 0.15) and extraversion (r= 0.1), on the other hand, we found only weak correlations. In practice, this only means for the time being that there is a certain similarity between the personalities of partners and that it is above all the similarity in the dimensions of "openness to experience" that is important, "Conscientiousness", and "Agreeableness arrives. Rammstedt and Schupp (2008) also analyzed their data in relation to relationship duration. Interestingly, it was found that the longer a couple had been together, the more similar they were in their personalities. Couples who have been together for more than 40 years showed an "openness to experience" on the personality dimension A correlation of r= 0.47. This is considered in psychology a very high correlation, which can be observed only in rare cases. The values are summarized compactly in the following table.
Personality congruence in couples
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Personality similarity as a predictor of relationship duration
In another study involving Rammstedt (Rammstedt, Spinath, Richter& Schupp, 2013), we used the same SOEP sample to examine the relationship between personality congruence and relationship duration. In this case, 4308 subjects participated in the study, of which 199 pairs separated during the study period. Personality was assessed at an interval of 4 years (2005 and 2009). In addition, the relationship status was queried annually until 2010. Here it was found that couples who stayed together throughout the survey period differed from couples who separated only in the dimension of "openness to experience" differed significantly. This difference, however, is high with r= 0.18. Stable couples were similar in the personality dimension with a correlation of r= 0.29, whereas unstable couples were similar only with r= 0.11. Since the study had two measurement points, it was also possible to test whether personality in couples converges over time. This could not be confirmed. In fact, the personality of the partners had almost not changed at all. The study by Rammstedt et al. (2013) thus gives indications that at least the personality dimension "openness to experience" is not a problem is suitable for predicting the relationship duration. In addition, it provides evidence that couples’ personalities do not converge over time but remain constant. However, the study has some weaknesses. Since all couples were already couples at the beginning of the study, it could be that personality congruence developed within the first phase of the relationship. Moreover, it is still not certain whether couples are similar to a particular degree or whether the individual partners to people in their peer group (similar interests/similar demographic characteristics) also have similar personalities.
Is the personality similarity in couples really greater than in noncouples??
For this paper, we have so far only looked at German studies, which is very encouraging, since in foreign studies one can never fully account for the effect of different cultures. However, the study now cited is from the U.S., and its design can answer many questions that would otherwise have remained completely unanswered. The study by Gonzaga et al. (2010) has the particular charm of including measures of couples before they even met. Now how could Gonzaga et al. (2010) accomplish this feat? The answer can be found in one manifestation of the modern partner-finding process, online dating. The study authors had data from the US dating site eHarmony at their disposal. eHarmony specializes in the mediation of long-term partnerships. Registration with the partner exchange includes filling out a questionnaire. In this, interests, current emotions and personality are measured. Even though this questionnaire is not specifically based on the Big Five, it is suitable for measuring the Big Five personality dimensions as markers. Finally, data were available for 417 people who met on eHarmony and eventually got married. The cooperation with eHarmony made it possible to clarify the question whether it is really personality congruence that promotes a partnership or whether congruence develops within the first relationship phase. It was also possible to test whether the personality congruence of couples is clearly different from the congruence of individual partners to their peer group. To answer the questions, the average correlation resp. The average coefficient of determination (r²) of the individual partners to all other persons included in the study was calculated. Thus, the personality similarity of the partners to ultimately randomly selected persons was calculated. Thus, it was possible to compare whether the personality congruence of the pairs differed significantly from the personality congruence of the individual partners to randomly selected persons. However, this was not enough for the creators. They calculated the same characteristic value not only for randomly selected persons, but also for those who were suggested to the test persons by the eHarmony partner algorithm as possible partners. Thus, it was possible to compare the personality congruence of couples with the personality congruence of individual partners to proposed individuals, i.e., their specific peer group.
Thanks to these quite complex calculations, the study leaders were able to determine precisely whether the personality of the subjects differed before and after they got to know their future spouses. It was also possible to test whether the personality similarity of the pairs was really greater than the similarity to randomly selected individuals or to individuals in the peer group. It is important to remember that the researchers had the same similarity data for interests and momentary emotions of the participants. Thus, they were able to examine like for like for interests and momentary emotions and compare all three categories personality, interests, momentary emotions).
Research results
It was found that the personality of the subjects had not changed before and after getting to know their later spouses. The personality similarity does not develop, but is given or not.
The study also showed that congruence is significantly higher in couples than in randomly selected individuals or groups. Subjects of their peer group. However, this is only true with respect to personality congruence and interest congruence, not emotion congruence. So the personality similarity of couples is greater than noncouples.
Personality similarity and relationship satisfaction
Gonzaga et al. (2010) also tested whether personality congruence is a good predictor of relationship satisfaction. For this they simply correlated the respective similarity quotient of the couples with the relationship satisfaction. Relationship satisfaction was measured at three different time points. The result was that personality congruence was the only one of the three domains (personality, interests, emotions) that was a significant predictor of relationship satisfaction at all three measurement time points. Interest and emotion congruence are significant predictors only for the latter two measurement time points. Beyond that, personality congruence is the best predictor at all times. The correlations are at least r= 0.3 from the second measurement point – a medium-strong correlation. Thus, 10 percent (r²) of the satisfaction in a partnership would be due to the degree of personality similarity
Personality similarity and partnership – a conclusion
There is mounting evidence that personality similarity benefits a relationship. Furthermore, it can be said with a high degree of certainty that the personality does not change due to a partnership. The circle of potential partners is thus strongly limited by one’s own personality, since the probability of a successful partnership decreases in the case of dissimilarity. Successful couples show a personality similarity in the dimensions of "openness to experience", "Conscientiousness" and "Compatibility of ca. r= 0,3. So the personalities agree within these dimensions ca. 10 percent (r²) agree. In particularly successful couples (relationship duration longer than 40 years), the similarity is even higher with r= 0.39, which corresponds to a personality match of ca. 16 percent (r²) corresponds to. Particularly high similarity among couples always exists in the dimension of "openness to experience". Satisfaction in a partnership is also influenced by personality. Ten percent (r²) of this depends on a couple’s personality similarity.
Bibliography
Bahns, Angela J.; Crandall, Christian S.; Gillath, Omri; Preacher, Kristopher J. (2017): similarity in relationships as niche construction. Choice, stability, and influence within dyads in a free choice environment. In: Journal of Personality and Social Psychology 112 (2), S. 329.
Buston, P. M. & Emlen, S. T. (2003). Cognitive processes underlying human mate choice. The relationship between self-perception and mate preference in Western society. Proceedings of the National Academy of Sciences, 100 (15), 8805-8810.
Gonzaga, G. C., Carter, S. & Galen Buckwalter, J. (2010). Assortative mating, convergence, and satisfaction in married couples. Personal Relationships, 17 (4), 634-644.
Rammstedt, B. & Schupp, J. (2008). Only the congruent survive-Personality similarities in couples. Personality and Individual Differences, 45 (6), 533-535.
Rammstedt, B., Spinath, F. M., Judge, D. & Schupp, J. (2013). Partnership longevity and personality congruence in couples. Personality and Individual Differences, 54 (7), 832-835.