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I need to graph the error between a set of observed values and an expected values.

I calculate the relative error for each point as:

(observed - expect) / expected 

This error however bounces up and down because the behaviour is sinusoidal. I want to make this error always a positive quantity. Is there an error measure like this? if so, what's its name?

I have looked for error measures, but all I find is absolute and relative, and I am interested in a positive relative error.

Any help appreciated, Ted.

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    You could multiply the result by its sign function ( http://en.wikipedia.org/wiki/Sign_function ) which will always make it positive ( this is identical to taking the absolute value ). Or just use the square root of the square, or , or.. :)2011-02-02

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I think it is sensible to use the following error measure:

$\frac{(O - E)^2}{E}$

This is related to the test statistic for Pearson's $\chi^2$ test.