The aging did occur to me, but without doing the numbers I doubt it would have an effect that fast on happiness, and certainly not that fast on misery.
Re immigration, research shows immigrants mostly take on the happiness of the country they move to, partly retaining their previous happiness. And as most recent immigration has been from less happy countries (eg Eastern Europe), I’d expect the effect to be a small fall in happiness not a rise. Though again without doing the figures I doubt it would be big enough to affect the general shape of the graphs.
The aging did occur to me, but without doing the numbers I doubt it would have an effect that fast on happiness, and certainly not that fast on misery.
Re immigration, research shows immigrants mostly take on the happiness of the country they move to, partly retaining their previous happiness. And as most recent immigration has been from less happy countries (eg Eastern Europe), I’d expect the effect to be a small fall in happiness not a rise. Though again without doing the figures I doubt it would be big enough to affect the general shape of the graphs.