You do not necessarily need a perfect 1-on-1 relationship between the used words and 'happiness', as long as this 'noise' is canceled out in the same way betwee

You do not necessarily need a perfect 1-on-1 relationship between the used words and 'happiness', as long as this 'noise' is canceled out in the same way between areas. And that's where there might be a problem, the results may (perhaps partially) reflect a structural difference of 'use of language' between areas.