A biomedical research company creates 2 similar real-time, nondestructive cancer diagnostic devices (X and Y) in the form of a pen. The pens are applied to the tissue surface for a few seconds, during which time each pen releases a single water droplet onto the tissue. The water droplet, which picks up small biomolecules from the tissue, is then sucked back into the pen and transferred via tubing to a mass spectrometer. The spectrometer performs a quick molecular analysis and determines whether the tissue is normal (noncancerous) or abnormal (cancerous). The devices allow surgeons to know which tissue to remove and which not to remove. The performance of Devices X and Y was compared using the same samples of tissue. The biomedical research company reported that, compared to Device Y, Device X is better at identifying cancerous tissue as abnormal but worse at identifying noncancerous tissue as normal. Based on this information, which of the following conclusions about the diagnostic devices must be true?

Question

A biomedical research company creates 2 similar real-time, nondestructive cancer diagnostic devices (X and Y) in the form of a pen.  The pens are applied to the tissue surface for a few seconds, during which time each pen releases a single water droplet onto the tissue.  The water droplet, which picks up small biomolecules from the tissue, is then sucked back into the pen and transferred via tubing to a mass spectrometer.  The spectrometer performs a quick molecular analysis and determines whether the tissue is normal (noncancerous) or abnormal (cancerous).  The devices allow surgeons to know which tissue to remove and which not to remove.  The performance of Devices X and Y was compared using the same samples of tissue.  The biomedical research company reported that, compared to Device Y, Device X is better at identifying cancerous tissue as abnormal but worse at identifying noncancerous tissue as normal.  Based on this information, which of the following conclusions about the diagnostic devices must be true?

Quizplus · Accepted Answer

Explanation: 11ec2b69_bdff_540d_8f63_bb008cc654d1_MD0005_00 In this example, the performance of 2 different cancer diagnostic devices (Device X and Device Y) is compared using the same samples of tissue. The devices identify cancerous tissue as abnormal and noncancerous tissue as normal. The ability to correctly identify cancerous tissue as abnormal is the sensitivity of the device, calculated as the number of true positives (TPs) divided by the total number of TPs and false negatives (FNs): Sensitivity = TP / (TP + FN). The false-negative rate (FNR) is the complement of the sensitivity (1 − sensitivity) and indicates the rate of negative test results in cancerous tissue. A device with high sensitivity (ie, correctly identifies cancerous tissue as abnormal) has a low FNR (ie, low rate of negative results in cancerous tissue). The ability to correctly identify noncancerous tissue as normal is the specificity of the device, calculated as the number of true negatives (TNs) divided by the total number of TNs and false positives (FPs): Specificity = TN / (TN + FP). The false-positive rate (FPR) is the complement of the specificity (1 − specificity) and indicates the rate of positive test results in noncancerous tissue. A device with high specificity has a low FPR. Compared to Device Y, Device X is better at identifying cancerous tissue as abnormal. This means that Device X is more sensitive than Device Y; consequently, it also has a lower FNR. In addition, Device X is worse at identifying noncancerous tissue as normal. This means that Device X is less specific than Device Y and consequently has a higher FPR (Choices D and E). (Choices A and C) In this case, the accuracy of a diagnostic device is the probability that it classifies tissue correctly. It is calculated as: Accuracy = (TP + TN) / (TP + TN + FP + FN). The positive predictive value (PPV) of a diagnostic device is the probability that an abnormal result correctly identifies cancerous tissue. It is calculated as: PPV = TP / (TP + FP). No information is given about the size of the samples studied or the exact sensitivity and specificity values; therefore, it is not possible to draw conclusions about the accuracy or PPV of the devices. Educational objective: More sensitive diagnostic tests (devices) have lower false-negative rates than less sensitive tests. More specific diagnostic tests have lower false-positive rates than less specific tests.

A Biomedical Research Company Creates 2 Similar Real-Time, Nondestructive Cancer