Post-Test Probability Calculator

Calculate Post-Test Probability



Formula

The formula to calculate the post-test probability is:

\[ \text{Pre Test Odds} = \frac{P}{1 - P} \]

\[ \text{Post Test Odds} = \text{Pre Test Odds} \times LR \]

\[ \text{Post Test Probability} = \frac{\text{Post Test Odds}}{1 + \text{Post Test Odds}} \]

Where:

Definitions

Example

Let's say the pre-test probability (P) is 0.012 and the likelihood ratio (LR) is 5. Using the formula:

\[ \text{Pre Test Odds} = \frac{0.012}{1 - 0.012} = 0.012 \]

[ \text{Post Test Odds} = 0.012 \times 5 = 0.06 ]

\[ \text{Post Test Probability} = \frac{0.06}{1 + 0.06} = 0.0566 \]

We get a post-test probability of approximately 0.0566 or 5.66%.