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Post-Test Probability Calculator

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:

Post-Test Probability: The likelihood of a particular condition or outcome being present after receiving additional information, such as test results or further evaluation.

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%.