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What is a Cumulative Summation Limit?
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What is a Cumulative Summation Limit?
Like the Westgard Rules, the Cumulative Summation Limit or Rule (CUSUM for short) has different approaches.
The CUSUM type used on the following pages is more sensitive to systematic than random error. Nevertheless, it does provide an easy means to detect impending problems.
CUSUM is calculated on worksheets like the one below.
Basically CUSUM works in the following manner: a decision limit is predetermined (See section E. on the right side of the chart, where CUSUM limit is defined as SD x 2.7), and when the CUSUM of control observations exceed this limit, one must look for error in the testing process.
The right side of the worksheet is used to determine the mean, standard deviation (SD), and CUSUM limit.
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