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|MainCategory=Biostatistics/Epidemiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Endocrine
|SubCategory=Endocrine
|Prompt=Two medical teams are conducting a similar study that aims 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?
|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?
|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.
|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.
|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.
|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.
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|References=First Aid 2014 page 51
|References=First Aid 2014 page 51
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=Statistics, Sensitivity, Specificity, Positive predictive value, Testing
|WBRKeyword=Statistics, Sensitivity, Specificity, Positive predictive value, Testing, Epidemiology
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 23:16, 13 December 2014

 
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.
References: First Aid 2014 page 51]]

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::