formulas Flashcards
What does sensitivity measure?
Sensitivity measures how well a test identifies those with the disease. A high sensitivity means fewer cases are missed.
What does specificity measure?
Specificity measures how well a test identifies those without the disease. A high specificity means fewer people without the disease are incorrectly labeled as having it.
What is Positive Predictive Value (PPV)?
PPV indicates the chance that someone who tested positive actually has the disease.
What is Negative Predictive Value (NPV)?
NPV indicates the chance that someone who tested negative really doesn’t have the disease.
What is the attack rate?
The attack rate measures the proportion of people in a population who become ill during a specific time period, typically an outbreak.
What is relative risk?
Relative risk compares the risk of disease in a group exposed to a potential risk factor to the risk in a group not exposed to that factor.
What is the formula for sensitivity?
Sensitivity = (True Positives) / (True Positives + False Negatives)
a / (a + c)
What is the formula for specificity?
Specificity = (True Negatives) / (True Negatives + False Positives)
d / (b + d)
What is the formula for Positive Predictive Value (PPV)?
PPV = (True Positives) / (True Positives + False Positives)
a / (a + c)
What is the formula for Negative Predictive Value (NPV)?
NPV = (True Negatives) / (True Negatives + False Negatives)
d / (b + d)
What is the formula for attack rate?
Attack Rate = (Number of people who became ill) / (Total number of people at risk)
a / (a + c)
What is the formula for relative risk?
Relative Risk = (Attack Rate in exposed group) / (Attack Rate in unexposed group)
What does high sensitivity indicate?
High sensitivity indicates that the test is good at finding people who have the disease.
What does high specificity indicate?
High specificity indicates that the test is good at correctly identifying people who don’t have the disease.
What does high PPV indicate?
High PPV means a positive test result is more likely to be a true positive.
What does high NPV indicate?
High NPV means a negative test result is more likely to be a true negative.
What are the key points of a good screening test?
A good screening test has high sensitivity and specificity, but there’s often a trade-off between the two.
What are the components of a contingency table?
True Positives (TP), False Positives (FP), True Negatives (TN), False Negatives (FN).
What does sensitivity (True Positive Rate) indicate?
If you have the disease, the test will correctly identify you as positive x% of the time.
What does specificity (True Negative Rate) indicate?
If you test positive, there’s a x% chance you actually have the disease.
What does Positive Predictive Value (PPV) indicate?
If you test positive, there’s a x% chance you actually have the disease.
What does Negative Predictive Value (NPV) indicate?
If you test negative, there’s a x% chance you really don’t have the disease.
