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6 Basic Statistical Tools

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6 BASIC STATISTICAL TOOLS
There are lies, damn lies, and statistics......
(Anon.)

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6.1 Introduction
6.2 Definitions
6.3 Basic Statistics
6.4 Statistical tests

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6.1 Introduction
In the preceding chapters basic elements for the proper execution of analytical work such as personnel, laboratory facilities, equipment, and reagents were discussed. Before embarking upon the actual analytical work, however, one more tool for the quality assurance of the work must be dealt with: the …show more content…

It is constituted by a combination of random and systematic errors (precision and bias) and cannot be quantified directly. The test result may be a mean of several values. An accurate determination produces a "true" quantitative value, i.e. it is precise and free of bias.

6.2.3 Precision
The closeness with which results of replicate analyses of a sample agree. It is a measure of dispersion or scattering around the mean value and usually expressed in terms of standard deviation, standard error or a range (difference between the highest and the lowest result).

6.2.4 Bias
The consistent deviation of analytical results from the "true" value caused by systematic errors in a procedure. Bias is the opposite but most used measure for "trueness" which is the agreement of the mean of analytical results with the true value, i.e. excluding the contribution of randomness represented in precision. There are several components contributing to bias:

1. Method bias

The difference between the (mean) test result obtained from a number of laboratories using the same method and an accepted reference value. The method bias may depend on the analyte level.
2. Laboratory bias

The difference between the (mean) test result from a particular laboratory and the accepted reference value.
3. Sample bias

The difference between the mean of replicate test results of a sample and the ("true") value of the target population from which the sample was

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