In the table below we show the S&P 500 Stock Index when it reversed down -10% or more over the past 10 years. Declines of -10% or more are not very common: they primarily happen during Cyclical Bear Markets. Out of 11 such declines, ALL OF THEM occured within a Cyclical Bear Market or marked the beginning of one. Over the past decade, when the stock index does decline -10%, on average it declined -22.3%. (Note: A -20% decline is commonly called a "bear market"). As a side note in regard to the average: 11 events isn’t enough to be statistically significant, so we look back 82 years. Since 5/14/1928 there were 92 declines of more than -10%. On average, they lasted 102 days and the average decline was -19.65%. That isn’t a lot different than the last decades mean of -22.3% over an average of 100 days. You can probably see how we use studies like these to quantify, define, and understand, what is normal, or not.
10% Gains also occured 11 times over the past decade. IN ALL INSTANCES, the 10% or more upward drifts occured within a bear market or it marked the end of a Cyclical Bear Market and the beginning of a new Cyclical Bull Market (no one knew that then, so we could also state that all instances occured within a Cyclical Bear Market). For example, the first low point that made the list was on 4/14/2000. The 3/24/2000 close of 1527 had previously marked the highest point and the beginning of a Cyclical Bear Market that lasted through the lowest close on 3/11/2000. That same date marked the beginning of the Cyclical Bull Market the continued through it’s end on 10/9/2007. You may notice that these dates are also marked on the table below since they were "picked up" by the 10% swings. Of course, the end of a Cyclical Bull Market is the beginning of a Cyclical Bear Market marked by that same date. Finally, the last 10%+ gain in the index started on 3/9/2009, which we now know was the beginning of the current Cyclical Bull Market as the Primary Trend today.