Re: [ccp4bb] Question about the statistical analysis-might be a bit off topic

[Kay Diederichs]

what I'm missing in those formulas, and in the Wikipedia, is a discussion of the prerequisites - it seems to me that, roughly speaking, if the standard deviation of B is as large or larger than the absolute value of the mean of B, then we might divide by 0 when calculating A/B . This should influence the standard deviation of the calculated A/B, I think, and seems not to be captured by the formulas cited so far.

best,

Kay

Am 20:59, schrieb James Stroud:

The short answer can be found in item 2 in this link:

http://science.widener.edu/svb/stats/error.html

The long answer is "I highly recommend Error Analysis by John Taylor:"

http://science.widener.edu/svb/stats/error.html

If you can find the first edition (which can fit in your pocket) then
consider yourself lucky. Later editions suffer book bloat.

James


On Jun 4, 2011, at 10:44 AM, capricy gao wrote:

If means and standard deviations of A and B are known, how to estimate
the variance of A/B?

Thanks.

--
Kay Diederichs                http://strucbio.biologie.uni-konstanz.de
email: kay.diederi...@uni-konstanz.de    Tel +49 7531 88 4049 Fax 3183
Fachbereich Biologie, Universität Konstanz, Box 647, D-78457 Konstanz

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