Cattle Inspection (1990) / Chapter Skim
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4 Statistical Considerations
4 Statistical Considerations
Pages 34-41
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From page 34... ...
It can help ensure that procedural or policy changes, personnel turnovers, inadvertent mistakes, poor training, or mechanical deficiencies do not establish an upward trend in defects that are detectable by inspection. CUSUM is a good choice to help control the process and ensure uniformity of processing.
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From page 35... ...
Use of CUSUM for Process Control MUM IS a widely accepted method tor maintaining process control In manufacturing products that must be kept within certain tolerances. At appropriate stages of production, product samples are examined for deviations from specified limits in composition, dimensions, or other features.
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From page 36... ...
The Sampling Basis for CUSUM If there is substantial variation in the average number of defects among lots, then the sampling for CUSUM needs to include an adequate number of subgroups from each lot. The plan for CUSUM monitoring of carcass and viscera includes the plant's sampling subgroups of three consecutive carcass sides with a frequency of one subgroup sample per hour and FSIS sampling subgroups of three consecutive sides every ~ hours; other products are sampled with different criteria.
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From page 37... ...
The probabilities of observing no defects among sampled units from single lots having an average of 0.1 defects per carcass are very high for the smaller lot sizes and decrease as the lot sizes increase. This is to be expected, since more carcass sides would be sampled from the larger lots for any given line speed.
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From page 38... ...
This demonstrated that a CUSUM-based inspection scheme will allow-with disturbingly high probability -- some defective meat to pass undetected in small lots and in plants with high line speeds, and reinforced the position that its use should be limited to process control. A second approach to studying the potential for defective cattle to pass the CUSUM monitoring process is presented in Figure 4-2.
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From page 39... ...
An attempt to sample adequately is built into SIS-C (see Chapter 3) by having plants institute their own quality control programs that are monitored by USDA.
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From page 40... ...
The company quality control program (QC) could be designed to detect visual defects exceeding acceptable limits among the cattle being processed and remove the defects or condemn the defective meat.
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From page 41... ...
Because of these limitations, greater flexibility must be built into the sampling process along with an emphasis on optimizing the quality of the final product rather than simply obtaining acceptable CUSUM scores. For CUSUM, or any comparable sampling system, the statistical basis for setting initial sample sizes and tolerance levels must be validated in a series of ongoing controlled studies.
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