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You are right. Note that the CV within the laboratories is smaller than the CV between the laboratories, except for wheat. This is reasonable as variations within the laboratory are usually smaller than between laboratories. Within the laboratories exactly the same methods are used, and the circumstances, e.g. temperature, chemicals used etc., are kept as constant as possible. Between laboratories the variations in methods and external circumstances are larger.

You are wrong. Variations within the laboratory are usually smaller than between laboratories; Within laboratories exactly the same methods are used, and the circumstances, e.g. temperature, chemicals used etc., are kept as constant as possible. Between laboratories the variations in methods and external circumstances are larger. This means that the CV between is usually larger than the CV within. This is also the case in this inter-laboratory trial, except for wheat.

In this interlaboratory trial both the within laboratory CV and between laboratory CV are calculated. Unfortunately they are not labeled in the table. Drag the labels above 'CV Within' and 'CV between ' to the right place in the table .

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Now you know which method was used to determine total fat in the biscuits. It is also important to critical judge the quality of the data. To get insight information of the quality of a laboratory you can ask a laboratory how they performed in an interlaboratory trial. Below you find the results of an interlaboratory trial in which the fat contents of several products is determined by various experienced food labs.

In an interlaboratory trial the precision of a measurement can be determined. Precision is a measure of the closeness of replicated analysis. If several measurements of one sample are performed the standard deviation (SD) of the analytical values can be calculated. SD and the coefficient of variation (CV) are measures for precision.