"Most of these couples were married, and people don't choose a marriage partner out of convenience."

I strongly object to the second clause here, at least historically. Frankly, I think historically people have married because of convenience, for some definition of 'convenience', statistically almost to the exclusion of attraction or commonality. That being said, I think historically people have had a lot fewer options and usually chosen to marry more for social, economic, political, and sustenance issues. That's changed in the last hundred years or so for more and more people (greater prosperity, less social pressure / greater social acceptance, etc.) so convenience has become a less common reason.