Marco Rubio delivered a speech on poverty today where he observed:
The truth is, the greatest tool to lift children and families from poverty is one that decreases the probability of child poverty by 82%. But it isn’t a government spending program. It’s called marriage.
Marriage is great. And it is true that a household with two adult members in it is much less likely to be poor than a household with one adult member. But even though conservatives say this a lot, I'm sometimes not sure that conservatives understand exactly why this is.
If you look up the Federal Poverty Guidelines you'll see that the way it works is that one person is poor if he or she earns less than $11,490. But due to household economies of scale, the FPG says that for two people to be non-poor they need to make $15,510 not $22,980. Indeed, the poverty line for a family of three is only $19,530—less than double the poverty line for one. Basically poverty is $11,490 for the first person plus $4,020 for each additional person.
So imagine a single mom earning the federal minimum wage of $7.25 an hour and working 40 hours a week, 50 weeks a year. She's got $14,500 a year in income which leaves her and her daughter below the poverty line. Now she meets another single mom who's in the exact same financial situation. The two of them fall in love, and since they live in an enlightened state they are able to get married. Now instead of two separate two-person households each earning $14,500 and being poor we have a single four-person household earning $29,000, which is well above the poverty line for four. They could even adopt a fifth child and still not be poor. Which is to say that marriage "lifts" families out of poverty not by increasing their incomes but by reducing what the federal government assumes their expenses to be.
Single people often have roommates for the same reason.
At any rate, conservatives aren't wrong about this. Having roommates really did greatly improve my personal finances when I was in my early 20's. And the same thing happened when my wife and I moved in together. We split the Internet bill, shared one Netflix account, etc. But the greater efficiency of shared expenses isn't really what's magical about marriage, and what's magical about marriage isn't really what leads to the poverty reduction.