Sensitivity, specificity, and likelihood ratios can be tricky concepts to understand and apply. This calculation sheet can help you better understand the meaning behind these terms.

Included in this sheet is a 2x2 table complete with calculations for the following:

Sensitivity

• The proportion of people WITH the condition who get a (+) test. Also known as the True Positive Rate.

Specificity

• The proportion of people WITHOUT the condition who get a (-) test. Also known as the True Negative Rate.

Positive Likelihood Ratio

• How much the odds of the condition increase based on a (+) test

Negative Likelihood Ratio

• How much the odds of the condition decrease based on a (-) test

Positive Predictive Value

• If (+) test, the probability of having the condition

Negative Predictive Value

• If (-) test, the probability of NOT having the condition

Diagnostic Odds Ratio

• Ratio of odds of (+) test if (+) for condition relative to the odds of (+) if (-) for condition.

Risk Ratio

• Ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.