WBR0599

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/Epidemiology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A lab technician is assessing the utility of a new lab machine that quantifies serum vitamin B12 levels. First, he measures the levels of vitamin B12 in 50 vials of serum of patients with neurological complaints who are known to have the exact same level of vitamin B12 deficiency. Following measurement of each vial, he compares the vitamin B12 levels among different vials and then compares their levels to the reference standard provided by the new machine's manufacturer. Following calculations, he notes that the results of the vitamin B12 levels are not entirely correct due to the presence of a random error despite the absence of a systematic error. Which of the following statements is entirely true regarding the technician's experiment?]]
Answer A	AnswerA::The experiment is precise but not accurate; it is reproducible but not valid
Answer A Explanation	AnswerAExp::The described experiment is accurate but not precise.
Answer B	AnswerB::The experiment is precise but not accurate; it is valid but not reproducible
Answer B Explanation	AnswerBExp::The described experiment is accurate but not precise.
Answer C	AnswerC::The experiment is accurate but not precise; it is valid but not reproducible
Answer C Explanation	AnswerCExp::The experiment 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 experiment is accurate but not precise; it is reproducible but not valid
Answer D Explanation	AnswerDExp::The described experiment is valid but not reproducible.
Answer E	AnswerE::The experiment is valid but precision cannot be determined based on the provided information. The experiment is thus reproducible with undetermined validity.
Answer E Explanation	AnswerEExp::Since the experiment contains a random error, it lacks precision.
Right Answer	RightAnswer::C
Explanation	[[Explanation::The experiment conducted by the lab technician assesses both precision and accuracy. Precision is defined as the consistency of a test; it measures its reproducibility and its reliability. It is best measured when samples of 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 best assessed by comparing samples to a reference standard, not to other samples. 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. As a result, the technician's experiment 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 to a reference standard. It assesses the trueness or validity of the experiment and may be reduced by a systematic error. In contrast, precision is measured by comparison to another samples. It assesses the reproducibility or reliability of the experiment and may be reduced by a random error. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::accuracy, WBRKeyword::precision, WBRKeyword::B12, WBRKeyword::vitamin, 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, WBRKeyword::vials
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