Happier countries tend to be richer countries. But more important for happiness than income are social factors like the strength of social support, the absence of corruption and the degree of personal freedom.
Over time as living standards have risen, happiness has increased in some countries, but not in others (like for example, the United States). On average, the world has become a little happier in the last 30 years (by 0.14 times the standard deviation of happiness around the world).
Unemployment causes as much unhappiness as bereavement or separation. At work, job security and good relationships do more for job satisfaction than high pay and convenient hours.
Behaving well makes people happier.
Mental health is the biggest single factor affecting happiness in any country. Yet only a quarter of mentally ill people get treatment for their condition in advanced countries and fewer in poorer countries.
Stable family life and enduring marriages are important for the happiness of parents and children.
In advanced countries, women are happier than men, while the position in poorer countries is mixed.