Happiness may be hard to define.  To get around that objective measures are used.

Are divorced people in general more unhappy?

You don't look at questionnaires.  You don't get a caliper out to measure smiles.  Instead you look at the mortality tables and you find out that children of divorced families live on average four years less.  If the children themselves become divorced add another four years.  Is there a relationship between happiness and life expectancy?  Last I knew bears were still shitting in the woods.

If you found 1000 men who all own tools to turn wood and split the men into groups A and B by some criteria.  Something that does not interfere with turning wood, and ask which group is happier? 

Group A made 20% more things than group B last year.



Depressed people would make the difference.  And you never measured depression.  You don't know how to do that, but you can count wooden bowls.

It is counterintuitive, but by measuring indicators you get objective results that are far better than asking someone if they are happy or not.  The key to getting good results is to find a lot of indicators.

In 1907, Sir Francis Galton asked 787 villagers to guess the weight of an ox. None of them got the right answer, but when Galton averaged their guesses, he arrived at a near perfect estimate. When I first discovered this factoid it seemed supernatural but it is not really.

Shoot a couple dozen arrows at a target, average the position and you likely have a bulls eye.