ClarityHow to use this tool
- Enter prior probability of a, probability of b given a, probability of b given not a.
- Select Calculate to view the result.
- Check the method and assumptions below before using the result.
Input reference and sample values
Use the units and choices shown for each field. Sample values are provided for practice, not as recommendations.
| Input | Format and units | Sample |
|---|---|---|
| Prior probability of A | Numeric value. Zero or positive. Maximum: 1. | 0.1 |
| Probability of B given A | Numeric value. Zero or positive. Maximum: 1. | 0.8 |
| Probability of B given not A | Numeric value. Zero or positive. Maximum: 1. | 0.2 |
Result for these sample inputs
0.307692308 probability
Select Try the example in the form to load these values and calculate them again. This replaces the current form inputs. Compare the result with the method and worked explanation below.
The method, explained
P(A given B) = prior × likelihood/[prior × likelihood + (1 − prior) × other likelihood].
Using prior probability of a = 0.1, probability of b given a = 0.8, probability of b given not a = 0.2, the result is 0.307692308 probability. Change these example inputs to match your task; use the method above to check each step.
What to keep in mind
Generic probability model; this tool does not interpret medical test results. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.
Methodology maintained by ClarityKit. How these tools are built and checked.