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We congratulate Salowi and colleagues on their study of the use of cumulative sum (CUSUM) to monitor competency in cataract extraction.1 However, there are two modifications that could be used to make their system more responsive and reliable.
The authors use a CSUM chart that fluctuates on only one side of the zero line. Traditionally, CUSUM charts fluctuate on both sides of the zero line.2 3 The consultant in their figure 1 performed 48 procedures and 43 were successful, while five were failures. The weight for a failure would be –1.791666, and for a success it would be +0.208333. Figure 1 depicts the traditional CUSUM graph with these data. Against this, the data from his trainee are also drawn. The trainee's CUSUM …
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