WBR0792

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/Epidemiology
Sub Category	SubCategory::Dermatology
Prompt	[[Prompt::A company is testing a new diagnostic tool for the detection of squamous cell carcinoma of the skin and comparing the results to biopsy specimens validated by professional dermatopathologists. The results are shown below. What is the probability that a person really doesn't have squamous cell carcinoma if his test result comes back negative? ]]
Answer A	AnswerA::82.75%
Answer A Explanation	AnswerAExp::This refers to the sensitivity.
Answer B	AnswerB::80%
Answer B Explanation	AnswerBExp::This refers to the positive predictive value.
Answer C	AnswerC::94.11%
Answer C Explanation	AnswerCExp::This refers to the NPV.
Answer D	AnswerD::93.02%
Answer D Explanation	AnswerDExp::This refers to the specificity.
Answer E	AnswerE::76.92%
Answer E Explanation	AnswerEExp::This does not refer to any particular value.
Right Answer	RightAnswer::C
Explanation	[[Explanation::The prompt in this question refers to the negative predictive value of the test being studied. To test sensitivity, specificity, and negative and positive predictive values of a certain test, results need to be compared to the gold standard test for the detection of the disease or outcome in question. The negative predictive value is the probability that a person really doesn't have the disease given that his test result is negative. The calculation is shown below. Educational Objective: The negative predictive value (NPV) of a test is the probability that a person really doesn't have the disease given that his test result is negative. NPV = [True negative/(True negative + False negative)] References: Chow S, Liu J. Design and Analysis of Clinical Trials, Concepts and Methodologies. John Wiley & Sons; 2013.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Negative predictive value, WBRKeyword::Positive predictive value
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::