Data from 6 million couples reveals a surprising trend in how we pick our partners

“Birds of a feather flock together” is a cliche for a reason when it comes to romantic relationships. Shared religious beliefs, values, political affiliation and even music taste all influence attraction and satisfaction in a relationship. But a recent study has now identified another unexpected factor that may bring couples closer together: sharing a similar mental health diagnosis.

The concept of romantic partners sharing a psychiatric diagnosis is not new. Indeed, between 1964 and 1985 several studies that explored the reasons why people choose their romantic partners included psychiatric diagnosis as a variable. However, no large-scale, cross-cultural investigation had been conducted until recently.

Using national health insurance data from more than six million couples in total, a team of researchers recently analysed the degree to which psychiatric disorders were shared between couples. They examined data from five million couples in Taiwan, 571,534 couples in Denmark and 707,263 couples in Sweden.

They looked at nine psychiatric disorders in their analysis, including depression, anxiety, substance-use disorder, bipolar disorder, anorexia nervosa, ADHD, autism, obsessive-compulsive disorder and schizophrenia. They found that people with a diagnosed psychiatric disorder had a higher likelihood of marrying someone with the same or a similar psychiatric disorder than they did of marrying someone who isn’t diagnosed with one.

While the finding is robust, the authors do acknowledge there are some limitations when interpreting the results.

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The first is that the timing of relationships and diagnoses were not recorded. This means that diagnosis could have occurred after the beginning of the relationship – and thus may not be the result of active choice.

Furthermore, a care provider’s own biases may influence how likely they are to diagnose a person with a specific mental health condition. Since many couples share the same family doctor, this could influence their likelihood of being diagnosed with a psychiatric condition — and could have biased the results seen in the study.

Finally, the authors stress their results are purely observational. This means they don’t explicitly consider the contributing factors as to why people with psychiatric diagnoses might be more likely to choose romantic relationships with each other.

However, there are several psychological theories that may help to explain this phenomenon.

Understanding this phenomenon

1. Assortative mating:

This theory assumes that we choose partners who are similar to us. Normally this is applied to personality and social factors (such as shared religious or socioeconomic background). But this recent study suggests that this choice may extend beyond these factors and into how we think.

So a person with a specific psychiatric disorder – such as anxiety or autism – may be drawn to someone with a similar psychiatric disorder because they share similar traits, values or approaches to daily life (such as prioritising structure and routine).

2. Proximity:

According to the mere exposure effect, we often choose relationships with people that we live or work in close proximity to – or otherwise spend time around.

People who share psychiatric diagnoses may be drawn to similar social situations. For example, people with substance use disorder may visit bars or other social settings where taking substances is more commonplace – and thus may be more likely to meet potential mates who are struggling with a similar disorder.

3. Attachment theory:

Attachment theory assumes that as infants, we develop a specific emotional bond to our primary caregivers. This early bond then shapes our subsequent emotional and psychological patterns of behaviour as we get older – and also influences what we’re looking for in a relationship.

So someone with an anxious attachment style (which can manifest as fear of abandonment, desire for closeness or need for reassurance) might feel drawn to a partner who has a similar attachment style or exhibits the kind of behaviour they desire – such as a partner who texts them all night when they’re apart. Even if this is not a healthy dynamic, the validation gained from a high-intensity relationship would likely make it hard to resist.

Research shows certain attachment styles are more common in people with specific psychiatric conditions. For example, anxious attachment style is more common in people who have anxiety, depression and bipolar disorder. This might help explain why the study found people with certain psychiatric conditions were more likely to be married to each other.

4. Social identity theory:

Social identity theory assumes that our self-esteem is gained through a sense of belonging within our social groups. So when you begin a relationship with somebody from within your social group, it boosts self-esteem as it brings a greater sense of belonging and feeling understood.

This might explain why people with the same psychiatric diagnosis (a social group) would be drawn to each other. Finding someone who understands and experiences the same struggles you do could help you bond and make you feel understood and validated.

What does this mean for us? Well, the results reported by this recent study can only tell us whether couples share psychiatric diagnoses. They don’t tell us the quality and duration of the relationship, nor do they account for individual differences which may also affect the relationship.

Ultimately, shared experiences promote closeness and empathetic communication for couples – and it stands to reason that this would extend to psychiatric diagnosis. Having a partner who understands and can relate to your mental illness can provide social support and validation that’s not available from someone who has never struggled with their mental health.

This article is republished from The Conversation under a Creative Commons license. Read the original article.