Stability and homogeneity of microbiological reference materials: some statistical models
Stabiliteit en homogeniteit van microbiologisch referentiemateriaal: enkele statistische modellen
Heisterkamp SH, Hoogenveen RT, van Strijp-Lockefeer NGWM, Hoekstra JA, Havelaar AH, Mooijman KA
RIVM Rapport 148602003
Microbiological reference materials are being developed by the RIVM since several years. These materials consist of capsules filled with milkpowder artificially contaminated with a bacteria test strain of choice (i.e. Escherichia coli, Enterobacter cloacae, Salmonella typhimurium). Both from longterm stability tests, and from short-term challenge tests at different storage temperatures, it is clear that these materials cannot survive forever. Standard statistical techniques for quality control, assuming both a stable process and the Normal distribution cannot be used. In this report we will deal with these non-standard problems.