Two childless singles, each earning $50,000 a year, marry.  Both keep working, living by the old-school principle of “share and share alike.”  What happens to their material standard of living?  If all depends on how rivalrous their consumption bundle is.

If all their goods are rival (like food), the answer is “Their standard of living stays the same.”  $50,000 times two divided by two equals $50,000.

If all their goods are non-rival (like Internet access), the answer is “Their standard of living doubles.”  They pool their money and buy a $100,000 lifestyle for both of them.

In the real world, of course, couples are rarely at either pole  Most goods are in fact semi-rival.  Consider housing.  If you share your home with a spouse, you don’t have as much space for yourself as a solitary occupant of the same property.  But both of you probably enjoy the benefits of more than half a house.  If a couple owns one car, similarly, both have more than half a car.  Even food is semi-rival, as the classic “You gonna eat that?” question proves.

Mathematically, married individuals’ utility looks something like this:




U=Family Income/2a

a=1 corresponds to pure rivalry: Partners pool their income, buy stuff, then separately consume their half.  a=0 corresponds to pure non-rivalry: Partners pool their income, buy stuff, then jointly consume the whole.

There’s little doubt that a<1.  This insight is even built into the official poverty line.  That’s why I say that being single is a luxury.  My question: Where does a typically lie in the real world?  Feel free to discuss variation by social class and nationality.  Please show your work.

P.S. If you know of academic references on this exact question, please share.