Question 1

ROC curves are most useful in assessing the performance of quantitative laboratory analyses because:&#10;A) multiple tests for the same analyte can be evaluated at one time.&#10;B) they can display performance of tests over the entire range of decision values.&#10;C) they allow specific reference intervals to be determined for each analysis.&#10;D) they can evaluate combination testing in a single plot.

Accepted Answer

ROC curves can display the performance of tests over the entire range of decision values, which is important in quantitative laboratory analyses as it allows for a comprehensive evaluation of the test's performance. A, C, and D are not necessarily true statements about the usefulness of ROC curves in assessing the performance of quantitative laboratory analyses.

Question 2

A receiver operating characteristic (ROC)curve is a plot of:&#10;A) systematic error against random error.&#10;B) tumor marker decision levels versus upper limit of reference intervals.&#10;C) true positives versus false positives.&#10;D) specificity of one method against the specificity of another method.

Accepted Answer

The ROC curve plots the true positive rate (sensitivity) against the false positive rate (1-specificity) for different cutoff values. This allows the visualization of the performance of a diagnostic test or predictive model and helps to identify the most appropriate cutoff value. Therefore, the correct answer is C, which refers to the plot of true positives and false positives.

Question 3

In regard to the number of true-positive and negative,and false-positive and negative,results in laboratory testing,the prevalence times the sensitivity is equal to the number of:&#10;A) true positives.&#10;B) false positives.&#10;C) true negatives.&#10;D) false negatives.

Accepted Answer

The prevalence times the sensitivity is the number of true positives. This is because prevalence represents the proportion of individuals in the population with the disease, and sensitivity represents the proportion of individuals with the disease who test positive. Multiplying these two values gives the number of true positives in the population.

Question 4

Calculate the sensitivity for the following data: in a group of 80 patients diagnosed with sickle cell disease,72 tested positively for it.The sensitivity of this test is:&#10;A) 111%.&#10;B) 100%.&#10;C) 90%.&#10;D) 75%.

Accepted Answer

Sensitivity = (true positives) / (true positives + false negatives)
In this case, true positives = 72 (those who have sickle cell disease and tested positive for it)
False negatives = Total number of patients with sickle cell disease - true positives = 80 - 72 = 8
Therefore, sensitivity = 72 / (72 + 8) = 0.9 or 90%.
So, the best choice is C) 90%.

Question 5

To calculate the sensitivity of a laboratory test to correctly classify true positives,one must first know the number of:&#10;A) true positives and false negatives.&#10;B) true negatives and false positives.&#10;C) true positives and false positives.&#10;D) false positives and false negatives.

Accepted Answer

Sensitivity measures the proportion of actual positives that are correctly identified as such (e.g., the percentage of sick people who are correctly identified as having the condition). To calculate it, one needs the number of true positives and the number of false negatives.

Question 6

A method that can be used to calculate the probability of a disease after new information is added to previously obtained information involves:&#10;A) likelihood analysis.&#10;B) sensitivity analysis.&#10;C) Bayes theorem.&#10;D) combination testing.

Accepted Answer

The method described is known as Bayesian analysis, which involves updating a prior probability with new information to calculate a posterior probability for a particular event or outcome. This is done using Bayes theorem, which relates the conditional probabilities of the event and the new information to the prior probability. Therefore, the correct choice is C, Bayes theorem.

Question 7

True negatives &#247; (false positives + true negatives)is the formula for determining:&#10;A) sensitivity.&#10;B) specificity.&#10;C) the odds ratio.&#10;D) the likelihood ratio.

Accepted Answer

This formula calculates specificity, which is the proportion of actual negatives that are correctly identified as negatives.

Question 8

Combination testing involves the use of multiple laboratory tests in an attempt to decrease costs or assist in diagnosing a specific disease.One of the problems with this type of testing is that:&#10;A) false-positive results increase.&#10;B) true-negative results increase.&#10;C) the prevalence of the disease increases.&#10;D) the predictive value of a negative test increases.

Accepted Answer

Using multiple tests increases the likelihood of detecting any possible abnormalities or disease, but it also increases the chance of false-positive results, leading to unnecessary treatments or interventions.

Question 9

A laboratory analysis that produces quantitative results with an infinite number of sensitivity and specificity pairs is referred to as a _____ test.&#10;A) predictive&#10;B) qualitative&#10;C) dichotomous&#10;D) continuous

Accepted Answer

A continuous test produces numerical results that can vary infinitely, rather than categorical results. Sensitivity and specificity are properties of a test's ability to correctly identify true positives and negatives, respectively, but they are not determinants of whether a test is continuous or not. Therefore, options A, B, and C are incorrect.

Question 10

In regard to clinical evaluation of method,a high clinical sensitivity means few false negatives.

Accepted Answer

A high clinical sensitivity means that the test can detect a high proportion of true positives, which in turn means that there are fewer false negatives.

Question 11

To calculate the predictive value of a positive test,which of the following should be known?&#10;A) Sensitivity only&#10;B) Specificity and prevalence only&#10;C) Sensitivity and specificity only&#10;D) Sensitivity,specificity,and prevalence

Accepted Answer

The answer of To calculate the predictive value of a...

Question 12

The probability of occurrence of a specific test value given that the disease is present divided by the probability of the same test value if the disease was absent is the:&#10;A) odds ratio.&#10;B) likelihood ratio.&#10;C) prevalence.&#10;D) predictive value.

Accepted Answer

The answer of The probability of occurrence of a specific...

Question 13

Nondiseased individuals that are classified as diseased by having a positive result on a specific laboratory test are considered:&#10;A) true positives.&#10;B) false positives.&#10;C) true negatives.&#10;D) false negatives.

Accepted Answer

The answer of Nondiseased individuals that are classified as diseased...

Question 14

The proportion of a population that has the particular disease being studied is referred to as the:&#10;A) prevalence.&#10;B) predictive value.&#10;C) positive value.&#10;D) clinical sensitivity.

Accepted Answer

The answer of The proportion of a population that has...

Question 15

What is the positive predictive value of a test in which 220 tested individuals with positive test results actually have the disease and 45 tested individuals with positive test results do not have the disease?

A) 16.9%
B) 66%
C) 83%
D) 120%

Accepted Answer

The answer of What is the positive predictive value of...

Deck 3: Clinical Evaluation of Methods