According to stereotype, the causality flows the other way, and having more money is likely to get you a girlfriend or wife. I suspect the stereotype is somewhat wrong and that more money leads to more free time, which leads to more friends and fun activities, which leads to a girlfriend or wife.

The stereotype is not wrong at all. Women are attracted to resources, and this is well established both in humans and in non-human animals. The reason is because women bear most of the inherent costs of child rearing (9 months gestation, breastfeeding, etc). However, providing sperm is not a very costly endeavor. Since females can afford to be choosy (that is, there are many males willing to spend the low cost of a load of sperm or two) they'll choose males with resources, all things being equal. Theoretically this male will lessen the inherent cost to the female by perhaps providing her with food during pregnancy and breastfeeding as well as for the child after it's weaned.

In some birds and mammals, females will choose males that have a bigger or better territory. In some cases, if a male has an especially big territory, the male will attract more than one female. (Emlen S. & Oring, L. 1977. Science 197 , 215-222)

In insects, which tend to not have bi-parental care, this is usually in the form of a "nuptial gift" which is basically a nutritious package that comes along with the sperm (Vahed, K. 1998. The function of nuptial feeding in insects: A review of empirical studies. Biol. Rev, 73:43-78.)

I agree too that women are attracted among other things (celebrity,intelligence, etc) to resources. I would be more specific and mention financial resources nowadays.

I don't mean to be sexist, but having a wife gives you more free time, not less.

You have the workload of a house divided into two instead of one. Even if your wife works it still ends up on the plus side.

It's not like you can code 24/7, you have to have some downtime. No reason not to spend that time with someone else.

A few correlations for your first point:

* Incentive to earn more - esp if we're looking at averages, the $0 startup guys will drag down the singles category.. The married people will likely be after a paycheque of some sort

* Age. - There's usually a link between age and income - and i'd guess at a link between age & partner status..

* Just realised that the raw data is actually there - so I shouldn't be guessing... Haven't got time this second to go through it - I'll try later..