Relationship between number of preparation errors and rate of inspection errors in four classes. The numbers of preparation errors in three classes (single similarity class, double similarity class, triple similarity class) were 338, 228, and 34, the rates of inspection errors in the same classes were 12.7% (43/338), 9.6% (22/228), and 2.9% (1/34), respectively. The bar and symbol represent the number of preparation errors and the rate of inspection errors, respectively. The differences in the rates of inspection errors were analyzed among four error classes (single, double, triple and no similarity class). There were no significant differences in the rates of inspection errors among four classes (P = 0.1305). The data were analyzed with a Chi-squared test. P values of <0.05 were considered to be statistically significant.