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- Thread starter frankmp40
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- #2

Borek

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What do you mean by "how to report"?

- #3

frankmp40

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I mean how to explain

- #4

Borek

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- #5

frankmp40

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Can I see the concentration is zero when it becomes slightly negative

- #6

Borek

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Even if you have a plot that looks perfectly linear and looks like it crosses 0,0 point, but you did the calibration for 10..100 range (of whatever unit), extrapolating the calibration outside of the 10..100 and saying "my concentration was measured to be 1" would be generally speaking a bad practice. In some cases it can be acceptable, but it depends on the application.

- #7

DrDu

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You should also never report an estimator without some confidence interval.

- #8

gravenewworld

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- #9

DrDu

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Of course he did. If not, there wouldn't be the parameter a for the curve.

One of the easiest ways to formulate the problem mathematically is the following.

The absorbance A is distributed (e.g. normally) around ##a+bc##, i.e.

##A\sim N(a+bc,\sigma)##. From the maximum likelihood principle we find c as that value which maximizes the probability to find the value of A actually measured under the constraint ##c\ge 0##.

That is ## \hat{c}=\mathrm{max}(0, (A-a)/b)##, where ##\hat{c} ## is the maximum likelihood estimator for c. If the standard deviation ## \sigma## depends on c, too, or if the distribution is not normal the result may be more complicated but the principle remains the same.

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