On 2010-12-08 20:10:13 +0000, Teignmouth said:

John,

If I use the SKEW function I get the following values:

Period Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1659-2009 (0.6) (0.5) (0.1) (0.1) 0.1 0.2 0.4 0.3 0.0 (0.1) 0.0
(0.2)
1971-2009 (0.8) (0.8) (0.2) 0.2 (0.1) (0.2) 0.8 0.4 (0.1) 0.0
(0.1) (0.8)

Now what do I do with the value and the Standard Deviation?

If I have a December mean for the period 1659-2009 of +4.1c, and the
STDEV is 1.7c, and the SKEW is -0.2c, do I get a revised STDEV of 1.5c
or 1.9c? Then do I use +4.1c and the revised STDEV x1 x2 x3 etc to
get the revised Standard Deviation thresholds?

Your help is much appreciated.

Thanks

No, just use the standard deviation. The skew is tiny. It's as good a
normal distribution as you'll ever get.

There are tests for the significance of deviation from normality, but I
wouldn't bother with them here. What do you want to do with your
standard deviation? Convert the current mean to a z-score?

--

Trevor
Lundie, near Dundee
www.trevorharley.com