spousal similarity for personality

Is spousal similarity for personality a matter of convergence or selection?

abstract:
We investigated whether spousal similarity for personality traits results from convergence (i.e., couples becoming more similar to one another over time) or selection (i.e., individuals selecting partners with similar traits) in a sample of 1296 married couples. Personality was assessed using the Multidimensional Personality Questionnaire. We evaluated whether similarity increased with increasing length of marriage. Evidence of spousal convergence was inconsistent across analyses, arguing against this mechanism as a compelling explanation for spousal similarity. Accordingly, selection processes may better explain spousal similarity in these data. The one exception might be for aggressive aspects of personality.

Even in a sample of young adults, Donnellan et al. (2007) found similarly sized correlations for Communal Positive Emotionality, Negative Emotionality, and Constraint (rs = .13, .17, and .22, respectively), suggesting young adults and those in established marriages have similar levels of similarity on personality dimensions. Couples were married an average of 19.8 years (SD = 5.4), with a range of 2–39 years Table 1 summarizes all analyses examining whether spousal similarity is associated with length of marriage.

In that paper
Personality was assessed using a 198-item version of the Multidimensional Personality Questionnaire.
Similarity was calculated using several methods, with linear and nonlinear regression analyses to predict the absolute value difference score between husbands and wives for all variables examined as suggested by Kenny, D. A., Kashy, D. A., & Cook, W. L. (Eds.). (2006). Dyadic data analysis. Guilford Press. [The method I had invented LIFEPROJECT METHOD is far superior] Specifically, although difference scores may capture level similarity (similarity in absolute trait scores of partners), they cannot capture shape similarity across dimensions of personality. To calculate profile correlations, individual trait scores were first meandeviated (following Kenny et al., 2006) and then a correlation was calculated between husbands' and wives' scores on the MPQ superfactors for each couple (i.e., all four wives' superfactor scores were correlated with all four husbands' superfactor scores). This procedure was repeated for the 11 lower-order scales. However, neither of these profile correlations were correlated with length of marriage (both rs = .04, p > .05).

You can also see "An exercise of similarity".

Understanding that spousal similarity is not primarily driven by convergence may prove important for research concerning personality traits and relationships. The results suggest that selection processes are probably more important than spousal socialization processes for understanding the origins of spousal similarity in personality. The one exception, again, might be traits related to aggression which deserves further attention. ... Assortative mating will also effectively increase the likelihood of genetic transmission of parental traits to their biological offspring (Fisher, 1918).

This paper is consistent with the Latest Research in Theories of Romantic Relationships Development, which outlines: compatibility is all about a high level on personality* similarity* between prospective mates for long term mating with commitment.
*personality measured with a normative test.
*similarity: there are different ways to calculate similarity, it depends on how mathematically is defined.
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