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Fisher's Exact Test Calculator — result sheet
Calculate an exact two-sided Fisher probability for a 2×2 contingency table with fixed margins.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: For each feasible a, P(a)=C(r₁,a)C(r₂,c₁−a)/C(N,c₁); the two-sided exact p-value sums feasible tables whose probability is no greater than the observed table.
The calculator keeps the four cell counts visible and evaluates the small-table hypergeometric model instead of using a large-sample chi-square approximation.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Row 1, column 1 — minimum 0; maximum 500
- Row 1, column 2 — minimum 0; maximum 500
- Row 2, column 1 — minimum 0; maximum 500
- Row 2, column 2 — minimum 0; maximum 500
Worked example
| Input | Value |
|---|---|
| Row 1, column 1 | 2 |
| Row 1, column 2 | 5 |
| Row 2, column 1 | 3 |
| Row 2, column 2 | 2 |
Observed table probability ≈ 0.2652; lower-tail p-value ≈ 0.3106; two-sided exact p-value ≈ 0.5581.
Assumptions and limits
- The table is 2×2 and its counts are nonnegative integers.
- The row and column margins are treated as fixed for the exact reference distribution.
- The result is a p-value calculation, not a measure of effect size or causal evidence.
- Large tables may be computationally burdensome and may be better served by an appropriate asymptotic method.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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