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Some remarks on the design of three-class sampling plans
1Institut für Biometrie und Informationsverarbeitung, Freie Universität Berlin, Germany.
Journal of Food Protection
|August 26, 1998
Summary
The three-class sampling plan for bacterial counts is widely used but can lead to lot rejection due to variability. This study proposes a method to determine appropriate microbiological limits (m and M) to balance risk and ensure good manufacturing practice compliance.
Area of Science:
- Microbiology
- Statistical Quality Control
- Food Safety
Background:
- Attributive three-class sampling plans are common for bacterial counts.
- Their performance relies on lot heterogeneity and the distance between microbiological limits (m and M).
- High heterogeneity or narrow limits increase the risk of rejecting acceptable lots.
Purpose of the Study:
- To investigate the impact of lot heterogeneity on bacterial count sampling plans.
- To develop a criterion for selecting appropriate distances between microbiological limits (m and M).
- To mitigate the risk of rejecting lots that meet good manufacturing practice (GMP) standards.
Main Methods:
- Analysis of a common three-class sampling plan (n=5; cm=2, cM=0).
- Assumptions of normally distributed logarithmic bacterial counts and an indifference lot (contamination at m).
- Calculation of acceptance/rejection probabilities based on lot variability and limit distance.
Main Results:
- Lot rejection probability increases with heterogeneity and proximity of m and M.
- A method is presented to gain insight into sample variability and limit distance.
- A criterion for choosing the m-M distance is developed based on acceptable heterogeneity.
Conclusions:
- The choice of distance between m and M is critical for three-class sampling plans.
- The proposed criterion helps select appropriate limits to avoid unnecessary lot rejections.
- This approach supports robust quality control while adhering to GMP.