TATITIC CALCULATOR
Fishers Exact Test
A precise tool.
What is the Fishers Exact Test & How does it work?
Fisher’s Exact Test is a statistical significance test used to examine the association between two categorical variables in a 2×2 contingency table, especially when sample sizes are small.
The test calculates the exact probability of obtaining a table at least as extreme as the observed one under the null hypothesis of independence.
p = frac{binom{a+b}{a}binom{c+d}{c}}{binom{n}{a+c}}
p = probability of the observed (or more extreme) table, n = a+b+c+d
Depending on the research question, the alternative hypothesis can be two‑sided, greater, or less, and the p‑value is summed over all tables that satisfy the chosen direction.
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Frequently Asked Questions
What is Fisher's Exact Test?
Fisher's Exact Test is a statistical test used to determine the significance of the association between two categorical variables in small sample sizes.
When should I use Fisher's Exact Test?
Use Fisher's Exact Test when you have a 2x2 contingency table and your sample size is small, or if the expected frequencies are less than 5.
How do I interpret the p-value from this test?
A low p-value (typically ≤ 0.05) indicates strong evidence against the null hypothesis, suggesting a significant association between the variables.
Can Fisher's Exact Test be used for larger sample sizes?
While Fisher's Exact Test is suitable for small samples, it can also be used for larger ones, though the chi-squared test might be more common in such cases.
What are the assumptions of Fisher's Exact Test?
The main assumption is that each subject contributes to only one cell in the contingency table and that the observations are independent.
How does this calculator compute the p-value?
The calculator computes the exact probability of obtaining a table at least as extreme as the observed one, using the hypergeometric distribution.
Can I use this test for more than two categories?
No, Fisher's Exact Test is specifically designed for 2x2 contingency tables. For more categories, consider using other tests like the chi-squared test or G-test.
Results are for informational purposes only and do not constitute professional advice.