Unexpectedly Intriguing!
29 July 2021

Long streaks and especially long losing streaks in the S&P 500 have become much less common during the past 20 years.

That change has come however as stock prices themselves have become more volatile. The following chart visualizes the daily percentage change from the previous days close for the S&P 500 from 3 January 1950 through 30 June 2021.

S&P 500 Daily Volatility (Percent Change Between Closing Value and Previous Trading Day's Closing Value), 3 January 1950 - 30 June 2021

In this chart, we see that large daily percentage changes have become more common in recent decades. To simplify the visualization of that change, we're calculated the standard deviation of the daily percentage change in the S&P 500 by decade, presented in the next chart, where we find the typical volatility among the U.S. stock market's largest stocks by market capitalization has increased.

Daily Volatility by Decade for S&P 500, Standard Deviation of Daily Percentage Change from Previous Close, 3 January 1950 - 30 June 2021

The final bar, for the 2020's, differs from the others in that it doesn't cover a full decade's worth of stock price changes. It covers the typical volatility observed to date in the year and a half from 2 January 2020 through 30 June 2021.

Still, it's a big jump over the preceding decade long periods, where we also see that the S&P 500 index in the decades of the 2000s have been considerably more volatile than the five decades that preceded them. The increase in the typical standard deviation indicates by decade bigger daily changes in stock prices have become more common in the 2000s.

That change offers a potential explanation for why losing streaks have become less common over the same period. Since the stock price volatility as measured by standard deviation has become larger than in previous decades, indicating larger daily changes when volatility breaks out, stock prices more quickly reach thresholds where investors buy the dips, which translates into shorter losing streaks.

Exit question: how profitable is buying big dips as a trading strategy?

References

Yahoo! Finance. S&P 500 Historical Data. [Online Database]. Accessed 2 July 2021.

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