The number of capsules to be used

For microbiological CRMs with high levels of cfp, tests are based on the geometric mean. The required number of capsules and replicates will depend on the level of differences the analyst wants to detect between the certified value and the laboratory geometric mean and on a and p. Of course, any difference is relevant and must be detected but this is unrealistic since the number of capsules to be used for such a level of acceptance would be infinitely large [13]. It is economically also unrealistic. 

Large differences between the certified value and a true laboratory geometric mean can be detected with a small number of capsules. 

Example use of Bacillus cereus (CRM 528) MEYP agar ISO 7932 method 

because the true laboratory geometric means are 32.5 and 87.6. The percentage of difference is computed from the lowest value, the certified value or the true laboratory geometric mean. 

The power is minimally equal to a = 0.05. When the true laboratory geometric mean is equal to the certified value the upper half of Table 3.4 applies and then the probability of concluding from the experiment that they are not equal is still a. 

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