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Pooled Standard Deviation

The document discusses the concept of pooled standard deviation, which is used to estimate precision when repeated measurements are not possible. It outlines the general formula for calculating pooled standard deviation for different samples and provides guidance on setting up experiments for evaluating repeatability and within-lab reproducibility. The document is authored by Ivo Leito from the University of Tartu's Institute of Chemistry in 2013.

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113 views1 page

Pooled Standard Deviation

The document discusses the concept of pooled standard deviation, which is used to estimate precision when repeated measurements are not possible. It outlines the general formula for calculating pooled standard deviation for different samples and provides guidance on setting up experiments for evaluating repeatability and within-lab reproducibility. The document is authored by Ivo Leito from the University of Tartu's Institute of Chemistry in 2013.

Uploaded by

omar rahmoun
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Pooled Standard Deviation

• If it is impossible to make many repeated


measurements with the same sample
Pooled Standard Deviation • Then precision can be estimated during longer
time in the form of pooled standard deviation

Ivo Leito
• Pooled standard deviation can be used to
University of Tartu
calculate:
Institute of Chemistry – Repeatability
2013 – Within-lab reproducibility

1 2

Pooled Standard Deviation Pooled Standard Deviation


• General formula for the case when experiment is
done with different samples, each measured • If the number of measurements made with each
repeatedly: sample was the same:

(n1  1) s1  (n2  1) s2  ...  (nk  1) sk s1  s2  ...  sk


2 2 2 2 2 2

l d 
spooled spooled 
n1  n2  ...  nk  k k
• Symbols: • Symbols:
– k number of samples – k number of samples
– s1, s2, etc are within sample standard deviations – s1, s2, etc are within sample standard deviations
– n1, n2, etc are numbers of measurements made for – n1, n2, etc are numbers of repeated measurements with
different samples every sample
3 4

Pooled standard deviation in practice

• How to set up • How to set up


experiment for experiment for within-
repeatability sr lab long-term
evaluation using reproducibility sRW
spooled? evaluation using
spooled?

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