How it works
Estimate the probability of exactly k events under a Poisson model with a constant rate and independent occurrences.
Inputs and units
| Input | Example value | What to enter |
|---|---|---|
| Expected events | 3 | Enter a numeric value. Use a non-negative value. Allowed range: 0–100. |
| Exact events | 2 | Enter a numeric value. Use a whole number. Use a non-negative value. Allowed range: 0–100. |
Worked example
Show example inputs and results
This example is generated by the same calculation engine using the starting values in the form. Your own inputs produce your own result.
- Expected events
- 3
- Exact events
- 2
Complete example results
- Result
- 0.22404181
Reading the result
Check the probability scale, sample size and assumptions stated by the method. A decimal probability of 0.5 represents 50%. Mean and spread inputs must describe the same dataset; the calculation does not validate those estimates.
Questions and answers
Can I use the example values for my own calculation?
The example values illustrate the calculation. Replace every input with your own information, especially dates, rates and the selected operation.
Which interval should the expected count describe?
Use the expected count for the same interval being evaluated. If the expected count is 3 per hour, use λ=3 for one hour; under the same constant-rate model, two hours use λ=6. The result is the probability of exactly k events.
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.