WBR0147
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| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Will Gibson and Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biostatistics/Epidemiology |
| Sub Category | SubCategory::Endocrine |
| Prompt | [[Prompt::Two medical teams are conducting identical studies that aim to detect an association between vitamin K deficiency and osteoporosis in France and Russia. Both teams are using the same test kit that is designed to measure vitamin K concentration in the blood. The sensitivity of the test is 90% and its specificity is 85%. According to previous studies, the prevalence of vitamin K deficiency is higher in Russia than it is in France. Based on the previous information, which of the following statements is correct?]] |
| Answer A | [[AnswerA::The ability of the test to detect vitamin K deficiency among people who actually have a low vitamin K level is higher in Russia than it is in France.]] |
| Answer A Explanation | [[AnswerAExp::The ability of the test to detect vitamin K deficiency among people who actually have a low vitamin K concentration refers to the sensitivity of the test. The sensitivity of the test is 90%, and this value is constant for a particular test. The sensitivity of this test is independent of the prevalence of vitamin K deficiency.]] |
| Answer B | AnswerB::The positive predictive value of the test is the same in France and Russia. |
| Answer B Explanation | [[AnswerBExp::The positive predictive value (PPV) refers to the probability that in the case of a positive test, the patient actually has the specified disease. This term is affected by the pre-test probability of a true positive based on the prevalence within a population. Since the prevalence of vitamin K deficiency is different in Russia from its prevalence in France, the PPV is not the same in these two countries.]] |
| Answer C | AnswerC::The positive predictive value of the test is higher in Russia than it is in France. |
| Answer C Explanation | [[AnswerCExp::The positive predictive value (PPV) refers to the probability that in the case of a positive test, the patient actually has the specified disease. A higher population prevalence leads to a higher positive predictive value.]] |
| Answer D | AnswerD::If the test is positive, the probability that the person truly has vitamin K deficiency is higher in France than it is in Russia. |
| Answer D Explanation | [[AnswerDExp::The PPV depends on the sensitivity, specificity, and prevalence of the tested item. Since the prevalence of vitamin K deficiency is lower in France than it is in Russia, then the PPV of this test is lower in France than it is in Russia.]] |
| Answer E | AnswerE::The positive predictive value of the test does not depend on the sensitivity and specificity. |
| Answer E Explanation | [[AnswerEExp::The PPV depends on the sensitivity, specificity, and prevalence of the tested item.]] |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The positive predictive value (PPV) is used to indicate the probability that in the case of a positive test, the patient actually has the specified disease. PPV is a function of the population sampled because if the pre-test probability of positive test is higher, a positive prediction is more likely to be correct. Since the prevalence of vitamin K deficiency is higher in Russia than it is in France, the PPV would be higher in Russia. Educational Objective: The PPV depends on the sensitivity, specificity, and prevalence of the tested item. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Statistics, WBRKeyword::Sensitivity, WBRKeyword::Specificity, WBRKeyword::Positive predictive value, WBRKeyword::Testing, WBRKeyword::Epidemiology |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |