Research into happiness suggests that our levels of happiness change throughout our lives.
People were asked how satisfied they are with their lives.
Most people start off happy and become progressively less happy as they grow older.
For many people, the most miserable period in their life is their 40s.
After that most people's levels of happiness climb.
This graph shows average life satisfaction based on extensive research from the British Household Panel Survey between 1991 and 2003.
It seems men are slightly happier on average than women in their teens, but women bounce back and overtake men later in life.
Women start with lower levels of average life satisfaction than men.
The low point seems to last for longer for women - throughout their 30s and 40s, only climbing once women reach 50.
Then women tend to overtake men.
Men start slightly higher than women on average, and their lowest point is their 40s, climbing again once they reach 50.
Graph source: British Household Panel Survey 1991-2003
Andrew Oswald, Department of Economics, University of Warwick and Nattavudh Powdthavee, Institute of Education, University of London.