Evidence of assortative mating according to personality was reported in a previous SOEP-based study (Rammstedt & Schupp, 2008). Based on population representative data of almost 7000 couples, high levels of congruence between spouses were found, which increased with marriage duration. Almost 5000 of these couples were tracked over a five-year period with personality assessed at the beginning and end of this time, which allowed us to investigate the relationship between personality congruence and marriage duration longitudinally. Using this data, we investigated (a) whether personality congruence is predictive for partnership longevity and whether congruence therefore differs between subsequently stable and unstable couples, (b) if stable couples become more congruent, and (c) if separated couples become less congruent with regard to their personality over time. The results provide initial evidence of personality congruence as a predictor for partnership longevity: the more congruent couples are in the personality domain of Openness, the more stable their partnership. In addition, we found no indications of an increase in personality congruence over time within the stable couples; within the separated couples, however, a strong decrease in congruence was detectable.
Birds of a feather flock together—this folk saying also seems to hold for personality. Assortative mating for personality was demonstrated in a previous study (Rammstedt & Schupp, 2008) based on population-representative data of almost 7000 couples, as well as in several other studies based on somewhat smaller and/or more selective samples (e.g., Bleske-Rechek et al., 2009, Gonzaga et al., 2010 and McCrae et al., 2008). However, assortative mating is not found to the same degree for all personality dimensions. In the aforementioned study by Rammstedt and Schupp, assortment was reported primarily for the Big Five domains Agreeableness, Conscientiousness, and Openness to Experiences, while for the remaining two domains Extraversion and Neuroticism, congruences were more or less non-existent.
In addition, Rammstedt and Schupp found that for the three domains Agreeableness, Conscientiousness, and Openness, congruence increased with marriage duration. There are two possible interpretations for this increase. On the one hand, it could be assumed that personality congruence is a major factor in the quality of a marriage. Lack of congruence might lead to increased friction and therefore end in separation or divorce. The finding that congruence is higher in long-term partnerships might therefore be moderated by the fact that incongruent partnerships ended earlier, resulting in a lower proportion of incongruent partnerships among the long-term couples in the sample. Consequently, we hypothesize personality congruence to be predictive for partnership longevity and assume congruence to be higher in couples who turn out to be stable than in couples separating in the years thereafter (Hypothesis 1). On the other hand, it could be argued that long-term couples become more similar in their personalities over time. For example, for someone less open to experience than his or her partner, joining this partner in cultural activities might make him or her more interested and thus more open. We could therefore assume a personality change towards higher congruence over time in stable couples (Hypothesis 2).
However, neither of the two alternative hypotheses is supported by data from previous studies. Gonzaga, Carter, and Buckwalter (2010), using data from an online relationship service, and Caspi, Herbener, and Ozer (1992), using data from the 20-year Kelly Longitudinal Study of couples, found no evidence that couples’ resemblance increased over time. In their study based on 51 student couples, Bleske-Rechek et al. (2009) found that intact couples did not differ less in their major personality dimensions than separated couples, thus contradicting our first assumption. As this study is based on a comparatively small and highly selective sample of young adults for whom partnerships and their duration presumably play a different role in their lives than for older respondents, this finding requires further investigation based on a less selective sample.
In addition to these two hypotheses, it might also be assumed that personality changes in couples who split up. A recent longitudinal study (Specht, Egloff, & Schmukle, 2011) showed that separation from a partner and divorce have different impacts on personality. Individuals who separated from their partner became more agreeable; divorced individuals became more conscientious and men became more open after separation from their female partners. Specht et al. (2011), however, investigated these effects only on the individual level, not on the level of couples. If, however, both ex-partners become more agreeable and/or more conscientious to a similar extent, this would not affect the congruence between their personalities. Thus, the study by Specht et al. can be regarded as providing initial evidence of personality change after separation and/or divorce. Whether this change also affects the personality congruence of the (ex-)couples has not been investigated to our knowledge. The supportive results for personality change after major life events, however, let us assume that personality congruence of couples should decrease after separation (Hypothesis 3)
In sum, the present study aims to investigate (a) whether personality congruence is predictive for partnership longevity and whether congruence therefore differs between couples who turn out to be stable versus unstable. In addition, we aim to test, (b) whether stable couples become more congruent over time and (c) whether separated couples become less congruent over time. To test these questions, we analyzed data of 4809 couples who were surveyed over a period of 5 years
