Causal chains: marriage, sex, money, happiness.

Jim Lindgren explains a study of of marriage, sex, money, and happiness by economists David Blanchflower and Andrew Oswald. It's nice that people are doing these studies and good that Lindgren is critiquing them, but I remain dubious. Do happy people have more sex, or does sex make people happy? Does marriage make people happier/richer/more sexually active, or are people with a happy nature, a good job, and a strong sex drive more likely to get married? These factors are interrelated in such complex and unknowable ways that it's hard to see how any collection of statistics can show what is cause and what is effect. Everyone is tempted to put first in the causal chain whichever thing (marriage, sex, money, or happiness) they most would like to see causing things.