Fisher Exact Test Calculator
Calculate conditional two-sided probability-ordering and one-sided Fisher exact p-values for a 2×2 count table.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Enumerate the hypergeometric distribution for feasible upper-left counts while fixing both row and column margins.
P(A=a)=C(success total,a)×C(failure total,row A total−a)/C(grand total,row A total)
Worked example
For the table [[1,9],[11,3]], the two-sided probability-ordering Fisher p-value is approximately 0.002759456. The sample cross-product odds ratio is 1/33.
Assumptions and input details
Nonnegative whole counts, positive row and column totals and grand total at most 10000. Log-combination probabilities are normalized numerically. The two-sided rule sums tables whose probability is no greater than the observed table, rather than merely doubling the smaller tail. No mid-p correction, odds-ratio confidence interval or causal claim is supplied. Large support tables display the first 199 and final row.
References: NIST: Fisher conditional hypergeometric calculation
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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