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Math Help - Standard curve query

  1. #1
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    Standard curve query

    Hi All,

    i'm looking for a little help understanding something, apologies if I have posted to the wrong place. I have a standard curve which interpolates a value with a percentage between 0-100.
    The curve performs well and we are using it to accurately predict unknows percentages. However, when plotting the data and fitting the curve if we include the reading for 100% the lower end of the curve performs very strangely (See attched files).
    Can anyone shed any light on what is happening here, my only thought is it is being caused but the curve reaching near vertical for the 100% readings.

    Thanks
    Attached Files Attached Files
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  2. #2
    MHF Contributor ebaines's Avatar
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    Re: Standard curve query

    It looks like your curve-fitting routine is using a 5th-order polynomial, and the data point at the end (the 100% data point) is not fitting that model very well. Hence the best fit curve has greater error for many of the other points. I notice that the curve includes the origin (0,0), yet from the data it looks like it that value may not be correct - can you try fitting a curve that starts with the 5% data point rather than 0%? I bet you'll get a better fit.
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  3. #3
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    Re: Standard curve query

    Quote Originally Posted by ebaines View Post
    It looks like your curve-fitting routine is using a 5th-order polynomial, and the data point at the end (the 100% data point) is not fitting that model very well. Hence the best fit curve has greater error for many of the other points. I notice that the curve includes the origin (0,0), yet from the data it looks like it that value may not be correct - can you try fitting a curve that starts with the 5% data point rather than 0%? I bet you'll get a better fit.
    Thanks ebaines. I'll try that.
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