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Author: Charley Big gold star, 5000 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 261252  
Subject: Re: Naive upside/downside calculation Date: 7/17/1999 1:48 AM
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Dave Goldman writes:
Standard Method

Mean 46.84% 46.84% 46.84%
StDev 24.77% 24.58% 24.95%

Thus in this case, rather than reporting the arithmetic mean annual return as 46.8% (+/-24.8%), we would report it as 46.8% (+25.0%/-24.6%).

Log Method

Actual Downside Upside
distribution distribution distribution
-------- -------- --------
Mean 44.89% 44.89% 44.89%
StDev 18.81% 19.45% 18.16%

Thus, the geometric mean annual return is 44.9% (+18.2%/-19.5%).

I admit I'm very light on the higher statistical concepts. But I do have a general understanding of the concept of sampling, mean, and SD. There is just something very different about the calculations when applying them to percentages and CAGRs. How can the SD change from 24.77% using the "standard" method to about 19% using Ln. It sure seems to me that the standard method should apply to the Upside returns. It is just that the mirror of the SD does not make sense when applied to the downside.

Would you look at the returns reported for the RS Bullet and try to interpret them using Logs. Maybe you need the entire return history. But still, I don't exactly see how using logs should change the SD on the Upside.


Good Returns
Charley Meng

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