[kurtosis]

why not take the simpler explanation that the reason families have broken up is that they actually weren't that happy?

Also why doesn't having multiple people in a family earning an income lead to an increase in security? i.e. the impact of a (e.g. job loss, illness) can be buffered by the other partner's income.

[billswift]

Only if they weren't already spending up to the limit (and past) of both incomes together. If one is working and loses his job, the other can get a job; if both are working and don't have any cushion, they are more likely to have a problem.