Biostatistics

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SnOut: Sensitive test to rule-out a disease. When a diagnostic test or sign has a high sensitivity, a negative result rules out the diagnosis.
Why SnOut? Sensitivity and Negative Predictive Value share FN. As Sensitivity increases toward 100%, FN decreases toward 0. As FN decreases toward 0, Negative Predictive Value increases toward 100%.
SpIn: Specific test to rule-in a disease. When a diagnostic sign or test has a high specificity, a Positive result rules in the diagnosis.
Why SpIn? Specificity and Positive Predictive Value share FP. As Specificity increases toward 100%, FP decreases toward 0. As FP decreases toward 0, Positive Predictive Value increases toward 100%.
SPECIFICITY = TN / TN+FP
SpIn: Specific test to rule In a disease. Why SpIn? Specificity and Positive Predictive Value share False positive (FP). As Specificity increases toward 100%, FP decreases toward 0. As FP decreases toward 0, Positive Predictive Value increases toward 100%.
Likelihood Ratio: The likelihood that a given test result would be expected in a patient with a disease compared to the likelihood that the same result would be expected in a patient without that disease.
Likelihood Ratio Positive (LR+): The odds that a positive test result would be found in a patient with, versus without, a disease.
Likelihood Ratio Positive (LR+) = Sensitivity / (1 - Specificity).
The probability of a test result being positive in a person with the disease divided by the probability of a test result being positive in a person without the disease.
LR(+) = [TP / (TP + FN)] / [FP / (FP + TN)]
Likelihood Ratio Negative (LR-): The odds that a negative test result would be found in a patient without, versus with, a disease.
Likelihood Ratio Negative (LR-) = (1- Sensitivity) / Specificity.
The probability of a test result being negative in a person who has the disease, divided by the probability of a negative test result in a person who doesn't have the disease.
LR(-) = [FN / (TP + FN)] / [TN / (FP + TN)]

Posted in: MEDICAL,USMLE