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maryam62

4 Posts
Posted - 02/10/2021 :  05:24:29 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hi
We used a nonlinear surface fit, and Poly2D Function, to fit our data. In the results section, figure below:



Is reduced chi square an Absolute error or relative error?

YimingChen

1618 Posts
Posted - 02/10/2021 :  09:24:16 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
It's defined as the residual sum of squared divided by the freedom. See page below:
https://www.originlab.com/doc/Origin-Help/NLFit-Theory#Reduced_Chi-Sqr

James
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maryam62

4 Posts
Posted - 02/10/2021 :  1:18:33 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Dear Yiming Chen
Thanks your response.
I read your suggested link. However, I could not conclude whether the reduced chi-square value was absolute or relative or none at all.
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YimingChen

1618 Posts
Posted - 02/10/2021 :  3:39:26 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

What do you mean by absolute/relative/none here? were you asking whether the reduced chi-square value changes if data scales?

James
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maryam62

4 Posts
Posted - 02/10/2021 :  4:01:39 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Can the value we report for this quantity (the reduced chi-square value) be an absolute or relative error, or is it not an error at all?
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YimingChen

1618 Posts
Posted - 02/10/2021 :  5:07:48 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
If you check equation (19) on that help page, the residual is calculated by yfit-y, so I guess it's absolute error? Is this what you mean?

James
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maryam62

4 Posts
Posted - 02/11/2021 :  06:23:06 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Dear Yiming Chen
Thanks your response.
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