Great Depression
The prolonged global downturn of the 1930s, with mass unemployment, bank failures and falling prices.
How to read the number
The key mechanism was the deflationary spiral: falling prices made real debts heavier, borrowers went under, banks withdrew credit, and demand fell further round the loop.
When the metric lies
It is used to prove that markets always recover, while the number of years that took, and how much the index membership changed meanwhile, go unmentioned.
Also known as: the great slump