Please remember there are different ways to assess personality and there are different ways to calculate similarity. Thus, "personality similarity" is a broad concept.
WorldWide, there are 5,000 -over five thousand- online dating sites
but no one is using the 16PF5 to assess personality of its members!
but no one calculates similarity with a quantized pattern comparison method!
PAPER "Assortative mating, convergence, and satisfaction in married couples"
Measures of personality were collected from a sample of 417 married couples who met via eHarmony since 2005 before they met and twice after they were married (2 years period). results indicate that similarity and convergence in psychological characteristics may benefit relationships and that while spouses may choose partners with similar personalities they do not become more like their partners in the early part of their marriage.
There are two reasons why romantic partners may be similar. The first is positive assortment, or the tendency for individuals to select similar partners. The second is convergence, or the tendency for partners to become more alike over time. Similarity in psychological characteristics predicts greater relationship satisfaction. Similarity in personality did not change over time, which is not surprising considering change in personality is gradual across adulthood.
If similarity is due to positive assortment, it suggests that the roots of relationship success may be established before individuals meet.
Participants: 417 married couples, who met via eHarmony, participated for a 2-year period.
The average male in the sample was 43.75 years old (SD = 11.08 years) and the average female was 40.73 years old (SD = 10.21 years).
They were first assessed at the time they registered for service. On average the second assessment took place 550 days after the original assessment and the final assessment took
place 1,350 days after the original assessment.
At the time of the final assessment, the average couple had been married for 2 years and 10 months with a range of 4 years and 8 months to 2 years and 2 months.
As a part of registration to the eHarmony service, all participants completed the eHarmony relationship questionnaires (EHRQ). Responses to EHRQ were used to match individuals with compatible potential partners. As a part of the eHarmony service, all participants were invited to communicate with between 1 and 1,079 other eHarmony users (M = 121.9, SD = 133.2). Each match met proprietary criteria for compatibility established by eHarmony.
eHarmony's proprietary matching algorithms were not used to determine similarity (between mates) in that study. Similarity was calculated using a couple centered approach (Klohnen & Mendelsohn, 1998; Luo & Klohnen, 2005).
As of August 2005 (the date of the initial follow-up survey), eHarmony had contact information on over 5,000 couples either married or engaged to be married. In August 2005 these couples were invited to participate in a marketing study designed to provide information on the efficacy of the eHarmony matching service.
POSTER "Similarity predicts relationship satisfaction in Brazil"
If eHarmony were a medicine, it will be performing as placebo.
eHarmony's personality similarity approach is correct, but how eHarmony assesses personality (intoxicated with Big5) and how eHarmony calculates similarity (low precision method) is incorrect.
I say the success rate* of eHarmony is less than 10%**.
*success rate == percentage of persons who leave the site because they found someone compatible.
**estimated by Fernando Ardenghi using reverse engineering.
The majority, over 90% of eHarmony's members are not going to achieve a long term relationship with commitment (or marriage) using that site.