Wellens Hans L L, BeGole Ellen A, Kuijpers-Jagtman Annemarie M
Department of Orthodontics and Craniofacial Biology, Radboud University Nijmegen Medical Centre Nijmegen, The Netherlands.
Department of Orthodontics, College of Dentistry, University of Illinois at Chicago, USA.
Eur J Orthod. 2017 Aug 1;39(4):358-364. doi: 10.1093/ejo/cjx002.
To assess the ANB angle's and Wits appraisal's diagnostic performance using an extended version of Receiver Operating Curve (ROC) analysis, which renders ROC surfaces. These were calculated for both the conventional and normalized cephalometric tests (calculated by exchanging the patient's reference landmarks with those of the Procrustes superimposed sample mean shape).The required 'gold standard' was derived statistically, by applying generalized Procrustes superimposition (GPS) and principal component analysis (PCA) to the digitized landmarks, and ordering patients based upon their PC2 scores.
Digitized landmarks of 200 lateral cephalograms (107 males, mean age: 12.8 years, SD: 2.2, 93 females, mean age: 13.2 years, SD: 1.7) were subjected to GPS and PCA. Upon calculating the conventional and normalized ANB and Wits values, ROC surfaces were constructed by varying not just the cephalometric test's cut-off value within each ROC curve, but also the gold standard cut-off value over different ROC curves in 220 steps between -2 and 2 standard deviations along PC2. The volume under the resulting ROC surfaces (VUS) served as a measure of overall diagnostic performance. The statistical significance of the volume differences was determined using permutation tests (1000 rounds, with replacement).
The diagnostic performance of the conventional ANB and Wits was remarkably similar for both Class I/II (81.1 and 80.75% VUS, respectively, P > 0.05). Normalizing the measurements improved all VUS highly significantly (91 and 87.2 per cent, respectively, P < 0.001).
The conventional ANB and Wits do not differ in their diagnostic performance. Normalizing the measurements does seem to have some merit.
使用扩展版的受试者工作特征曲线（ROC）分析来评估ANB角和Wits评估法的诊断性能，该分析可生成ROC曲面。针对传统和标准化头影测量测试（通过将患者的参考标志点与普氏叠加样本均值形状的标志点进行交换来计算）均计算了这些曲面。所需的“金标准”是通过对数字化标志点应用广义普氏叠加（GPS）和主成分分析（PCA），并根据患者的PC2分数对患者进行排序而统计得出的。
对200张头颅侧位片的数字化标志点（107名男性，平均年龄：12.8岁，标准差：2.2；93名女性，平均年龄：13.2岁，标准差：1.7）进行GPS和PCA分析。在计算传统和标准化的ANB及Wits值后，通过不仅改变每个ROC曲线内头影测量测试的临界值，还在沿PC2的-2至2个标准差之间的220个步骤中改变不同ROC曲线的金标准临界值，构建ROC曲面。所得ROC曲面下的体积（VUS）用作整体诊断性能的指标。使用置换检验（1000轮，有放回）确定体积差异的统计学意义。
对于I/II类，传统ANB和Wits的诊断性能非常相似（VUS分别为81.1%和80.75%，P>0.05）。测量值的标准化显著提高了所有VUS（分别为91%和87.2%，P<0.001）。
传统ANB和Wits在诊断性能上没有差异。测量值的标准化似乎确实有一定优点。
