Quick guide
How to use this calculator
- Enter the observations, probabilities, model parameters, or summary statistics requested by the visible labels.
- Keep every value on the same scale and confirm that the selected sampling relationship, distribution, and tail convention match the question you are investigating.
- Read the result together with its assumptions and interpretation. Statistical output summarizes uncertainty under a model; it does not repair biased data or establish causation.
Calculation method
How the probability tree calculator works
Path probability multiplies along branches; a marginal probability adds its mutually exclusive complete paths.
The four leaf paths partition the sample space and reveal exactly which first-stage branches contribute to the second event.
Worked example
Probability Tree example
If P(A)=0.3, P(B|A)=0.8, and P(B|not A)=0.2, then P(B)=0.38.
Path probability multiplies along branches; a marginal probability adds its mutually exclusive complete paths.
Supported inputs
Precision and limits
Model and design
The tree models two exhaustive binary stages; entered conditional probabilities must refer to the same B event under A and not A.
Numerical scope
Inputs use double-precision numerical methods with guarded domains. Datasets accept up to 10,000 finite plain-decimal values. Extremely large parameters or probabilities deep in a numerical tail may require specialist statistical software.
Interpretation
The four leaf paths partition the sample space and reveal exactly which first-stage branches contribute to the second event.
Decision boundary
The calculator does not validate how data were collected, diagnose dependence or bias, choose a scientifically meaningful effect, or replace review by a qualified statistician for consequential research, medical, regulatory, safety, or policy decisions.
Privacy
Entered values and calculated results stay in this browser and are not sent to an analytics service.
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