Research on
compatibility
Primal Match is grounded in peer-reviewed research on what actually creates stable, satisfying relationships. We focus on the factors shown to matter most: each person's own personality, where a pair is similar, shared health-oriented lifestyles, and value compatibility. Every study we rely on is linked below.
The HEXACO personality model
in compatibility research
Primal Match's compatibility engine is built on the HEXACO model of personality structure, a six-factor framework developed through large-scale cross-cultural lexical studies (Ashton & Lee, 2007). HEXACO extends the traditional Five-Factor Model by introducing a distinct Honesty-Humility dimension, which has been shown to predict prosocial behavior, relationship trust, and long-term partnership stability independent of the other factors.
The six dimensions (Honesty-Humility (H), Emotionality (E), Extraversion (X), Agreeableness (A), Conscientiousness (C), and Openness to Experience (O)) capture personality variance that is directly relevant to relationship formation and maintenance. Our matching score weights these dimensions according to the literature summarized below, which points to two things: who each person is matters more than how alike two people are, and Emotionality (the HEXACO cousin of neuroticism) adds up across a couple rather than cancelling out.
In-app, the assessment uses the IPIP-HEXACO scales (Ashton, Lee, & Goldberg, 2007), a public-domain item set developed via the International Personality Item Pool that measures the same six HEXACO factors. The IPIP version lets us deliver a validated assessment without the licensing constraints of the proprietary HEXACO-PI instrument.
Honesty-Humility
The HEXACO factor behind sincerity, fairness, and modesty. It carries the most weight in our score, both as a level (two honest people) and as alignment (two people with the same relationship to rules and fairness).
Emotionality
Emotional reactivity, anxiety, and sentimentality. We score it additively: each person's own level counts, and the sum of a couple's neuroticism predicts lower satisfaction (Cheon et al., 2024), so two highly reactive partners get an extra flag. Being similar on E is not, by itself, a plus.
Extraversion
Social self-esteem, boldness, and liveliness. Higher extraversion goes with higher satisfaction on average (Malouff et al., 2010), but differences in social energy are among the easiest for couples to manage, so it carries the least weight in our score.
Agreeableness
Patience, forgiveness, and flexibility. Higher agreeableness is linked to higher relationship satisfaction across studies (Malouff et al., 2010), so it counts as a level in our score as well as a point of alignment on conflict style.
Conscientiousness
Discipline, organization, and deliberation. Nine years of couple data show that a person's own conscientiousness predicts their sustained satisfaction (Bach, Koch & Spinath, 2024), so it is one of the three traits in our level term.
Openness to Experience
Intellectual curiosity, aesthetic sensitivity, and unconventionality. The evidence for openness is weaker than for the traits above; we treat it as a question of alignment (shared interests and ways of spending free time) with moderate weight.
How the score is built. Personality compatibility is half similarity (how close two people sit on each trait, weighted toward Honesty-Humility and Conscientiousness) and half level (the pair's average Honesty-Humility, Agreeableness and Conscientiousness). Emotionality is scored additively rather than by similarity, for the reasons above. Personality is then blended with lifestyle (diet, training) into one number, and that number is shown as where the pair stands among other Primal Match pairs, so a typical pair reads about 65 and a rare one reads 90 or more. Trait percentiles are approximate until Primal Match has enough assessments to compute its own norms. When you open a potential match's profile you see where the two of you align, where you sit far apart, and a plain-language note on what each difference tends to mean.
The peer-reviewed studies below are the empirical foundation for the score and for the watch-outs we show.
How personality traits shape lasting relationships
The Five-Factor Model of personality and relationship satisfaction of intimate partners
Across 19 samples and 3,848 participants, lower neuroticism and higher agreeableness, conscientiousness, and extraversion were each associated with higher relationship satisfaction, for men and women alike.
Why it matters for Primal Match: These are level effects, about who each person is, which is why half of our personality score is the pair's level on Honesty-Humility, Agreeableness and Conscientiousness and why Emotionality counts for each person on its own.
View Study →Relationship satisfaction and The Big Five: utilizing longitudinal data covering 9 years
Nine annual waves of 486 couples: a person's own lower neuroticism and higher conscientiousness predicted their sustained relationship satisfaction, while their partner's traits added little.
Why it matters for Primal Match: The strongest personality signals are each person's own levels, so our score rewards a pair where both people are steady and reliable rather than a pair that merely matches.
View Study (Open Access) →Is actual similarity necessary for attraction? A meta-analysis of actual and perceived similarity
Perceived similarity (feeling similar to your partner) remains a strong predictor of attraction and satisfaction even in established relationships.
Why it matters for Primal Match: Feeling similar matters even when measured similarity predicts less, which is why we show the pair where they align and explain the differences instead of hiding them behind a single number.
View Study →Predicting relationship and life satisfaction from personality in nationally representative samples from three countries
In large Australian, British and German samples, each partner's own traits predicted relationship satisfaction far better than how similar the two partners were.
Why it matters for Primal Match: Similarity-only matching rests on the weakest part of the literature. Our score keeps similarity for what it is good for (alignment you can feel) and adds the level term the evidence supports.
View Study →
Why emotional stability matters in matching
Totality model of neuroticism: The sum of spousal neuroticism and marital satisfaction
In two studies of South Korean couples (204 and 251 couples), the combined neuroticism of both spouses showed a strong negative association with marital satisfaction. The simple "sum" model performed as well as more complex actor–partner, similarity, and synergy models.
Why it matters for Primal Match: This is the model we use. Each person's Emotionality lowers the pair's score on its own, two highly reactive partners get an extra watch-out, and a calm partner helps without being treated as a cure.
View Study →The role of shared fitness in relationships
Better together: The impact of exercising with a romantic partner
Exercising together with a partner increases positive mood during the activity and improves overall relationship satisfaction.
Why it matters for Primal Match: Supports matching people who share active, health-oriented lifestyles, a core part of the keto/MAHA/non-toxic community.
View Study →Why beliefs are a filter, not a score
Religious Affiliation and Marital Satisfaction: Commonalities Among Christians, Muslims, and Atheists
Across a large cross-cultural sample, marital satisfaction looked much the same for Christians, Muslims, and atheists; the clearer difference was between men and women. The study does not test whether partners who share a faith are happier.
Why it matters for Primal Match: We do not score religion. It is a filter you can set yourself, because the evidence that affiliation itself drives satisfaction is thin, while what you want in a partner on this point is yours to decide.
View Study (Open Access) →