Department of Radiology, The University of Chicago, 5841 South Maryland Avenue, MC 2026, Chicago, IL 60637, USA.
Acad Radiol. 2013 Jul;20(7):897-907. doi: 10.1016/j.acra.2013.03.007. Epub 2013 May 8.
Human observers often do not produce empirical operating points near the northeast corner of the receiver operating characteristic (ROC) plot, and thus the local shape of the population ROC curve is unknown.
We call attention to occult abnormalities and propose that considerations by human observers of the prior probability of occult abnormalities can cause the shape of the local population ROC curve to be convex, a straight line, or concave near the northeast corner of the ROC plot. We further conducted a set of simulated detection-task (without-search) experiments with human observers and, mathematically, with an ideal observer and a model observer. In the experiments, we used signals, pseudo-signals that were similar to signals, and random image noise. The relative frequency of occult signals was controlled in the experiments.
In the simulated experiments, the population ROC curve of the ideal observer was always convex, but those of the model observer and of human observers were convex, a straight-line, or concave, depending on the relative frequency of occult signals. The population ROC curve for the model observer was identical to that for the ideal observer when knowing the relative frequency of occult signals was not important for the ideal observer, and it was similar to that for human observers otherwise.
Observer consideration of the prior probability of occult abnormalities is important in ROC studies and could cause unexpected shapes of the local population ROC curve. Absence of empirical operating points near the northeast corner of the ROC plot may be caused by occult abnormalities.
人类观察者通常不会在接收器操作特性 (ROC) 图的东北角落附近产生经验操作点，因此群体 ROC 曲线的局部形状未知。
我们提请注意隐匿性异常，并提出人类观察者对隐匿性异常的先验概率的考虑可能导致局部群体 ROC 曲线在 ROC 图的东北角落附近呈凸形、直线形或凹形。我们进一步进行了一系列具有人类观察者的模拟检测任务（无搜索）实验，以及理想观察者和模型观察者的数学实验。在实验中，我们使用了信号、类似于信号的伪信号和随机图像噪声。隐匿信号的相对频率在实验中受到控制。
在模拟实验中，理想观察者的群体 ROC 曲线总是凸形的，但模型观察者和人类观察者的群体 ROC 曲线则是凸形、直线形或凹形，这取决于隐匿信号的相对频率。当理想观察者不知道隐匿信号的相对频率不重要时，模型观察者的群体 ROC 曲线与理想观察者的群体 ROC 曲线相同，否则则与人类观察者的群体 ROC 曲线相似。
观察者对隐匿性异常的先验概率的考虑在 ROC 研究中很重要，并且可能导致局部群体 ROC 曲线的意外形状。ROC 图的东北角落附近没有经验操作点可能是由隐匿性异常引起的。
