Topic42

No, likelihood ratios are not influenced by disease prevalence.

Due to the low number of false negatives.

Likelihood Ratios (LRs) are a statistical measure used to assess the diagnostic value of a test.

Sensitivity = True Positives (TP) / (True Positives (TP) + False Negatives (FN)).

An LR- less than 0.1 significantly decreases the probability of disease ('rules out' disease).

Balancing sensitivity and specificity is crucial depending on the clinical context and the consequences of false positives versus false negatives.

Internal validity concerns the accuracy of conclusions within the context of the study.

Lower NNT values indicate more effective interventions.

LR- is the probability of a negative test result in a diseased individual divided by the probability of a negative result in a non-diseased individual.

Specificity = True Negatives (TN) / (True Negatives (TN) + False Positives (FP)).

The Number Needed to Treat (NNT) is the number of patients who need to be treated to prevent one additional adverse outcome.

PPV is the probability that a person with a positive test result actually has the disease.

Validity refers to the extent a test measures what it claims to measure.

NNT = 1 / Absolute Risk Reduction (ARR), where ARR = Control Event Rate (CER) - Experimental Event Rate (EER).

Reliability indicates the consistency and reproducibility of test results over repeated applications.

Sensitivity measures the test's ability to correctly identify those with the disease (true positive rate).

PPV increases with higher disease prevalence; fewer false positives relative to true positives.

NPV is the probability that a person with a negative test result does not have the disease.

External validity relates to the generalizability of results to broader populations.

NNT provides a tangible measure of treatment efficacy and helps in comparing the benefits and costs of treatment options.

NPV = True Negatives (TN) / (True Negatives (TN) + False Negatives (FN)).

An LR+ greater than 10 significantly increases the probability of disease ('rules in' disease).

Increasing sensitivity often results in decreased specificity, and vice versa. Maximum sensitivity may lead to more false positives, while maximum specificity may lead to more false negatives.

The NNT is calculated as the inverse of the absolute risk reduction (ARR).

PPV = True Positives (TP) / (True Positives (TP) + False Positives (FP)).

LR+ is the probability of a positive test result in a diseased individual divided by the probability of a positive result in a non-diseased individual.

Specificity measures the ability to correctly identify those without the disease (true negative rate).

In low prevalence settings, even tests with high sensitivity and specificity can have low PPV due to the higher number of false positives compared to true positives.