A final consideration in developing a sampling plan is to minimize the overall vari- ance for the analysis.

**Minimizing the Overall Variance**

A final consideration in developing a sampling plan is to minimize the overall vari- ance for the analysis.
Equation 7.2 shows that the overall variance
is a function of the variance
due to the method and the variance
due to sampling. As we have seen, we
can improve the variance due to sampling
by collecting more samples of proper
size. Increasing the number of times we analyze each sample improves
the variance due to the method.
If *s _{s}*2 is significantly greater
than

If *s _{m}*2 is
significantly greater than

Unfortunately, the simple
situations just described are often the exception. In many
cases, both the sampling variance
and method variance
are significant, and both
multiple samples and replicate analyses
of each sample
are required. The over-
all error in this circumstance is given by

7.8

Equation 7.8 does not have a unique
solution because different combinations of *n*_{s}
and *n*_{r} give the
same overall error.
The choice of how many
samples to collect
and how many times
each sample should
be analyzed is determined by other concerns, such as the cost of collecting and analyzing samples,
and the amount
of available sample.

Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail

Modern Analytical Chemistry: Obtaining and Preparing Samples for Analysis : Minimizing the Overall Variance |

**Related Topics **

Privacy Policy, Terms and Conditions, DMCA Policy and Compliant

Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.