Volatility comes in spells
Descriptive, not a test
Today's volatility is in the second fifth of its history. After sessions in that fifth, the median volatility over the next month was 15.0%, and the market fell 10% or more within three months 17% of the time, over about 23.6 independent three-month periods. After the calmest fifth the same two figures were 11.9% and 12%. After the most volatile fifth they were 28.9% and 42%, and across all sessions 15.6% and 22%. Each day's fifths are set from the history known on that day. This describes one market, and we registered no test on it.