How many cases need to be reviewed to compare performance in surgical pathology?

Recent studies have shown increased interest in measuring error rates in surgical pathology. We sought to determine how many surgical pathology cases need to be reviewed to show a significant difference from published error rates for review of routine or biopsy cases. Results of 4 series with this type of diagnostic material involving a total of 11,683 cases were reviewed to determine the range of published false negative, false-positive, typing error, threshold error, and clinically significant error rates. Error rates ranged from 0.00% to 2.36%; clinically significant error rates ranged from 0.34% to 1.19%. Assuming a power of 0.80 and a 1-sided alpha of 0.05, the number of cases needed to be reviewed to show that a laboratory with either twice or one half the published error rate was significantly different from the range of published error rates varied from 330 to 50,158. For clinically significant errors, the number of cases varied from 665 to 5,886. Because the published error rates are low, a relatively large number of cases need to be reviewed and a relatively great difference in error rate needs to exist to show a significant difference in performance in surgical pathology.