Statistical quality assurance:
how to use your microbiological data more than once

Monitor trends in the microbiological quality of your food materials, to identify and prevent potential problems, with the help of statistical quality assurance.

Microbiological analysis of raw materials provides data that can be used to compare the microbiological quality of the material against agreed quality criteria. Decisions on whether to accept or reject particular batches of material might be made on this basis. However, these data, which can be expensive to gather, can be further exploited by using statistical quality assurance to identify trends - increasing your awareness of potential problems and your understanding of the supplier or process.

This review, which includes a spreadsheet-based tool, was developed by a group of microbiologists and statisticians to help food companies understand and exploit statistical quality assurance. Taking you step-by-step through the approach, the review will enable you to use statistical quality assurance to:

• Identify trends that could reflect underlying quality problems
• Ensure that the last CCP (critical control point) verification check is not drifting from the previous good results
• Compare the quality of one supplier with another
• Check whether a supplier can meet set criteria
• Demonstrate to a customer your quality record and that your processes are, microbiologically, in control
• Monitor your laboratory's performances on duplicate analyses as well as scores from ring trials and methods controls

Contents:

• Introduction
• Microbiological data
• Looking for changes
  - Plotting graphs of the data
  - Turning the graphs into SQA charts
  - Calculations
  - Tests for special causes
• Comparing with specifications
• Using the spreadsheets
• Further reading

Note: One free copy of the spreadsheet is provided with each copy of the review. Its use requires a PC with Excel and assumes proficiency with this package. The spreadsheet cannot be provided in any other package. CCFRA does not undertake to provide support to users of this spreadsheet and is not able to provide support in the use of Excel. Both the spreadsheet and the guide are protected by copyright law.