Negative Predictive Value Formula Quiz and Flashcards

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Questions and Answers

In a diagnostic test, which value indicates the probability of a positive test being a true positive?

Sensitivity

Specificity

Positive Predictive Value (correct)

Negative Predictive Value

What is the formula for calculating Sensitivity?

TN / (TN + FN)

TP / (TP + FP)

TN / (TN + FP)

TP / (TP + FN) (correct)

Which factor has a strong impact on predictive values in diagnostic tests?

Specificity

Sensitivity

Prevalence (correct)

Accuracy

Which value represents the probability of a negative test being a true negative?

Negative Predictive Value Signup and view all the answers

What is the formula for calculating Specificity?

TN / (TN + FP) Signup and view all the answers

If the prevalence of a disease increases, what is likely to happen to the Positive Predictive Value of a diagnostic test?

Increase Signup and view all the answers

In a diagnostic test, what does Sensitivity measure?

Ability to detect true positives Signup and view all the answers

Which impact do higher specificity values have on the Negative Predictive Value of a diagnostic test?

No Impact Signup and view all the answers

What does diagnostic sensitivity measure?

The capacity of a test to correctly identify True Positives Signup and view all the answers

What is diagnostic specificity focused on?

Identifying True Negatives Signup and view all the answers

In relation to test results, what does it mean when the cut-off value changes from A to B?

Decreased sensitivity and increased specificity Signup and view all the answers

How does an increase in sensitivity affect the False Negative rate?

Increases the False Negative rate Signup and view all the answers

How does a high cut-off value influence the predictive value of a positive test result?

Decreases the predictive value of a positive test result Signup and view all the answers

What is the key trade-off when trying to increase both sensitivity and specificity?

Decreased test accuracy Signup and view all the answers

What is the impact of increasing sensitivity in a diagnostic test?

More false positives Signup and view all the answers

What does specificity represent in a diagnostic test?

The percentage of true negatives Signup and view all the answers

When the cut-off value changes from figure A to B, what happens to the specificity?

Increases Signup and view all the answers

Which parameter helps in determining the probability that a test-positive animal is truly diseased?

Sensitivity Signup and view all the answers

In clinical practice, what does test predictive value represent?

The probability that a test-positive result is truly diseased Signup and view all the answers

What trade-off is mentioned when discussing sensitivity and specificity in diagnostic tests?

Trade-off between sensitivity and specificity Signup and view all the answers

What happens to specificity when sensitivity is increased?

Specificity decreases Signup and view all the answers

Which parameter helps in determining the probability that a test-negative animal is truly healthy?

Specificity Signup and view all the answers

What is the main purpose of diagnostic tests as mentioned in the text?

To confirm or exclude a diagnosis Signup and view all the answers

Which phase of testing is described as involving the handling and analysis of the specimen?

Analytical phase Signup and view all the answers

What factors may determine the selection of a diagnostic test according to the text?

All of the above Signup and view all the answers

Which parameter represents a diagnostic test's ability to correctly identify those with the disease?

Sensitivity Signup and view all the answers

If a diagnostic test has high specificity, what can be concluded about its ability?

It can rule out individuals without the disease effectively. Signup and view all the answers

How does changing the cut-off value of a diagnostic test affect sensitivity and specificity?

Increasing the cut-off decreases sensitivity and increases specificity. Signup and view all the answers

What is meant by positive predictive value in the context of diagnostic testing?

The probability that a person with a positive test result actually has the disease. Signup and view all the answers

What is the impact of increasing sensitivity on false negatives in a diagnostic test?

The number of false negatives decreases. Signup and view all the answers

Study Notes

Diagnostic Testing

A diagnostic test can be divided into 4 categories: True Positive (TP), False Positive (FP), False Negative (FN), and True Negative (TN)
Cut-off value: a value that divides test results between positive or negative
Sensitivity: measures the capacity of a test to correctly identify positive individuals (TP) = TP × 100 / (TP + FN)
Specificity: measures the capacity of a test to correctly identify negative individuals (TN) = TN × 100 / (TN + FP)

Predictive Values

Predictive values: probability of a test result being a true positive or true negative
Positive Predictive Value (PPV): probability of a positive test being a true positive = TP × 100 / (TP + FP)
Negative Predictive Value (NPV): probability of a negative test being a true negative = TN × 100 / (TN + FN)
Prevalence has a strong impact on predictive values

Impact of Prevalence and Cut-off Changes

Increasing sensitivity: more false positives, fewer false negatives
Decreasing specificity: more false negatives, fewer false positives
Changes in cut-off value: affects sensitivity and specificity

Understanding Test Results

Test results can be divided into four categories: true positive, false positive, false negative, and true negative
Importance of diagnostic tests: confirms or excludes diagnosis, determines treatment strategies, and identifies new pathogens

Phases of Testing

Pre-analytical phase: test selection, sampling, storage, and transportation
Analytical phase: performing the test
Post-analytical phase: reporting results and interpretation

Test Selection and Sample Considerations

Test selection: determined by type of pathogen, type of sample, test characteristics, phase of disease, availability, and cost
Sample considerations: correct selection, collection, storage, and transportation of samples

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Description

Test your knowledge on predictive values and prevalence in medical testing. Learn about positive predictive value, negative predictive value, specificity, and how prevalence affects predictive values. Understand the importance of these concepts in assessing the accuracy of medical tests.

Predictive Values and Prevalence Quiz