Can you measure disaster risk in-time?
Use out-of-sample implied volatility at an extreme below-the-money strike price vis-a-vis an implied volatility at-the-money. Remarkably, crash risk jumped after the 1987 crash. Then it was stable, elevated from about 1997 to about 2000, and again after about 2010—but not greatly so.
Can crash risk explain the equity premium?
You could have purchased insurance against crash risk. This is the cost of this insurance. You can decide when to purchase it, because you know the cost ahead of time. In recent decades, the cost is under 1% per annum.
Ergo: Market-crash risk is not unimportant, but it is also not as large as it is often made out to be.