I fully understand that it went up quickly by a lot, and have no problem with the recent drop. But why did it seem to instantly become so volatile? It seems like every day it's up or down 2% or more. Or is it just that it's very visible and that many stocks exhibit similar trading behavior?


1 Answer 1


I looked at data from Sept 2010 to present:

  • SPY (the S&P ETF) Standard deviation over this time - 1.21
  • MSFT - 1.40
  • AAPL - 1.65

Standard deviation is what shows the spread shape of returns over time, and it meanS that about 2/3 of the time, AAPL return was within +/- 1.65 higher/lower than the daily average return which was .21 %. Not sure where to go with this except to suggest that in fact, AAPL is more volatile than the S&P and even another random tech company. With time, I'd probably come up with a list of stock more volatile. I know that when I look at a list of stocks I track on Yahoo, there are always a few that are just as volatile on a given day.

Excel makes the above analysis easy to do for a given stock, and it's actually an interesting exercise, at least for me.
Disclaimer - the shape of stock returns is not a bell curve, and STdev is just a best fit.

Edit - given more time to tinker on excel, it would be interesting to see how the stock's volatility tracked over the years, did it increase or does it feel that way due to the high price? A $20 swing on a $600 stock is the same as a $2 swing on a $60 stock, yet "up $20" sounds huge.

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