A question about errors!

kresten no-sp at m.org
Thu Aug 2 07:39:33 EST 2001


Under some conditions you can use a simple expression for the propagation of
errors,

let f = F(x1, x2, ..., xn)

then

sigma(f)^2 ~ sum_i=1,n (sigma(xi)*(df/dxi))^2
where df/dxi are partial derivatives.

In your case f = f(A,B) = ln(A/(A-B))
calculate the partial derivatives and plug in known values of A, B and
sigma(A) and sigma(B).

good luck
Kresten


""Cliodhnqa"" <cliodhnascanlon at hotmail.com> wrote in message
news:OE47OeIiGXix4A2DreB00004708 at hotmail.com...
Hello!
Can anyone tell me how to calculate the error of the following. I have an
equation that is ln or log X. X is calculated from the following equation:
ln [A/(A-B)]

A & B have both an error. It's so long since I've done any of these stats
calculation...I'd be most grateful if anyone can help me out. Thanks a lot.
S.






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