cross-tables and diagnostic performance parameters

The 23 indeterminate ultrasound results were grouped as either test positive or test negative and a total of 126 (7ⅹ18) cross tables were made. The sensitivity, specificity, PPV, NPV, and accuracy of the ultrasound to predict the deep location of parotid tumors were calculated in every 126 cross tables.将23例不确定的超声检查结果划分为阳性检测结果与阴性检测结果两类，共构建126张（7×18）列联表。针对全部126张列联表，逐一计算超声检查预测腮腺肿瘤深部位置的灵敏度、特异度、阳性预测值（Positive Predictive Value, PPV）、阴性预测值（Negative Predictive Value, NPV）以及准确度。