WBR0599

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/Epidemiology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A lab technician is assessing a novel method to quantify serum vitamin B12 levels. First, he uses the new method to measure the levels of vitamin B12 in sera of 50 patients previously known to have identical vitamin B12 levels. Then, the technician compares the obtained vitamin B12 levels among each other, and also compares their levels to the reference standard. The technician finally concludes that a large random error is present despite the absence of a systematic error. Which of the following statements is entirely true regarding the technician's novel method?]]
Answer A	AnswerA::The method is precise but not accurate; it is reproducible but not valid
Answer A Explanation	AnswerAExp::The described method is accurate but not precise.
Answer B	AnswerB::The method is precise but not accurate; it is valid but not reproducible
Answer B Explanation	AnswerBExp::The described method is accurate but not precise.
Answer C	AnswerC::The method is accurate but not precise; it is valid but not reproducible
Answer C Explanation	AnswerCExp::The method is truly accurate (valid) but not precise (reproducible) because of the absence of a systematic error and presence of random error, respectively.
Answer D	AnswerD::The method is accurate but not precise; it is reproducible but not valid
Answer D Explanation	AnswerDExp::The described method is valid but not reproducible.
Answer E	AnswerE::The method is valid but precision cannot be determined based on the provided information. The method is thus valid with undetermined reproducibility.
Answer E Explanation	[[AnswerEExp::Since the method contains a large random error, it lacks precision. Recall that there is no strict quantitative cutoff for the variance of a test result to conclude that a test is precise. However, we can conclude that the error is large from the prompt.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::The experiment conducted by the lab technician assesses both precision and accuracy of his novel technique. Precision is defined as the consistency of a test; it measures its reproducibility and its reliability. It is optimally assessed when sample results from the same test are compared against each others (not against a reference standard). Lack of precision is a result of random error during experimentation. In contrast, accuracy measures the trueness or the validity of a test. It is optimally assessed by comparing sample results to a reference standard, not to other sample results of the same machine. Lack of accuracy is a result of systematic error during experimentation. As a result, all sample data will skew in a similar fashion from the true value due to the presence of an error that affects all the samples equally. In this vignette, the technician's novel method is accurate due to lack of systematic error but not precise due to the presence of a random error. As such, it is valid/true but not reproducible/reliable. Educational Objective: Accuracy is measured by comparison of sample results to a reference standard. It assesses the trueness or validity of a technique or method and may be reduced by a systematic error. In contrast, precision is measured by comparison of sample results to other samples that have been similarly tested. It assesses the reproducibility or reliability of a technique or method and may be reduced by a random error. References: First Aid 2014 page 54]]
Approved	Approved::Yes
Keyword	WBRKeyword::Accuracy, WBRKeyword::Precision, WBRKeyword::B12, WBRKeyword::Vitamin, WBRKeyword::Method, WBRKeyword::Technique, WBRKeyword::Reproducible, WBRKeyword::Reproducibility, WBRKeyword::Reliable, WBRKeyword::Reliability, WBRKeyword::Valid, WBRKeyword::Validity, WBRKeyword::True, WBRKeyword::Trueness, WBRKeyword::Systematic, WBRKeyword::Random, WBRKeyword::Error, WBRKeyword::Reference, WBRKeyword::Standard, WBRKeyword::Sample
Linked Question	Linked::
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