Other research shows that those in friendship-based love relationships feel they have a highly likable partner, and that shared companionship is an important part of the love.

A study of 622 married individuals revealed that those with higher scores on the friendship-based love scale also reported more relationship satisfaction, greater perceived importance of the relationship, greater respect for their spouse, and felt closer to their spouse.

Companionate love is more closely associated with relationship satisfaction than is passionate love – the type of romantic love based on intense feelings of attraction.

Once a romantic couple forms, we're more likely to look for more egalitarian splits of power and divisions of labor.

We hold our relationships to higher standards than we have in previous decades.

I enlisted the help of Monmouth University Polling Institute to investigate.

To help figure out how many best-friend couples are out there, we asked 801 adults across the United States the following question: 'Do you consider your partner to be your best friend or do you call somebody else your best friend?

In fact, companionate love is more closely associated with relationship satisfaction than is passionate love – the type of romantic love based on intense feelings of attraction and preoccupation with one's partner.

The overall numbers from this recent poll dwarf the earlier reported rate of best-friend romantic partners.

In particular, couples now expect their relationships to promote personal growth and help individuals fulfill their own goals.

For example, your partner should help you become a better person by teaching you new things like how to make the perfect creme brulee, taking you places like the cool new trampoline park and opening your eyes to new perspectives such as the benefits of eating a more vegetarian-based diet.

In order to hit all these self-improvement targets, you may need more from a spouse or romantic partner than was expected in years past – and a partner who is also your best friend may be a step in the right direction.