View Single Post
  #16 (permalink)  
Old 03-July-2007, 12:40 AM
JohnW JohnW is offline
Established Member
 
Join Date: Jan 2004
Location: Yorkshire Consulate, Seattle
Posts: 880
Default

Quote:
Originally Posted by aurora View Post
No, it isn't.

If the distribution is normal, about 99.5% of the observations would fall within +/- 3 SD of the mean.

You've got daily data for 24 years? About 8700 days? And the best evidence you have is just slightly over 3 standard deviations?

Get thee to an introductory statistics course.
He's aggregating the ~8700 data points into 29 totals, so he's not looking directly at the individual values. I'm more concerned about his assumption of normal distribution - rainfall data are emphatically not normally distributed, and the totals are going to be highly sensitive to a handful of outliers. (In other words, a couple of good downpours might account for most of the total for a given aggregate).

I agree entirely with your last paragraph, though.