Chi-squared Test Calculator
🧬 Genetics & evolution. Use the Chi-squared test (two groups) formula to find χ², observed group 1, expected group 1, observed group 2, expected group 2: pick the value you want, type the others, and the answer updates as you go.
With 2 groups (1 degree of freedom), χ² below 3.84 means the difference is just chance (p > 0.05).
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| χ² | no unit |
| Observed group 1 | no unit |
| Expected group 1 | no unit |
| Observed group 2 | no unit |
| Expected group 2 | no unit |
Worked example
Find the χ² when Observed group 1 = 80, Expected group 1 = 75, Observed group 2 = 20, Expected group 2 = 25.
Using ² = ((O1 - E1)²)/E1 + ((O2 - E2)²)/E2: χ² = 1.3333.
Frequently asked questions
What is the formula for Chi-squared test (two groups)?
² = ((O1 - E1)²)/E1 + ((O2 - E2)²)/E2. With 2 groups (1 degree of freedom), χ² below 3.84 means the difference is just chance (p > 0.05).
What do the letters stand for, and what units are used?
χ², Observed group 1, Expected group 1, Observed group 2, Expected group 2.
How do you calculate χ²?
Put the values into ² = ((O1 - E1)²)/E1 + ((O2 - E2)²)/E2. For example, with Observed group 1 = 80, Expected group 1 = 75, Observed group 2 = 20, Expected group 2 = 25, χ² = 1.3333.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (χ², observed group 1, expected group 1, observed group 2, expected group 2) and fill in the others: it rearranges the formula for you.
