Using predefined values to identify chemically relevant factors

8 Using predefined values to identify chemically relevant factors 

When using predefined values [4] no statistical test is performed to identify relevant factors. So-called chemically relevant effects of factors are identified by comparing them with predefined critical values for the responses. 

The authors also define a standard error although differently from the one previously given in equation 12. For that reason, when speaking about the standard error defined in reference [4] it will be indicated as the relative standard deviation of the experiments (RSD) since in fact that is what is calculated. 

The calculated effects are normalized on a scale of 100%. The experiments in the design are duplicated. The effect and the relative standard deviation are calculated as follows  

In this method the effect values Ex(%) are compared with predefined values to identify relevant factors. These predefined values do not represent the limit of statistical significance but the limit of chemical relevance. These limits represent acceptable variations that are allowed to occur in practice. A list of these predefined values for the effect of factors on responses measured in HPLC is shown in Table 3.20. 

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