For 2×2 tables, Prism offers both the chi-square test and Fisher’s exact test. Fisher’s exact test is an test that calculates a precise P value, whereas the chi‑square test provides an approximation. Fisher’s exact test is particularly valuable when your sample size is small or when expected cell frequencies fall below 5. For large samples, the two tests yield nearly identical results, and the difference between exact and approximate P values becomes trivial.
To create a "verified" report using , you must go beyond just providing a
χ2 = 14.4 p-value = 0.0001 Degrees of freedom = 1
Determines if your observed categorical data matches a theoretical or expected distribution. chi square graphpad verified
The Chi-Square test produces a p-value, which indicates the probability of obtaining the observed frequencies (or more extreme frequencies) assuming that the two variables are independent. If the p-value is below a certain significance level (usually 0.05), the null hypothesis of independence is rejected, indicating that there is a statistically significant association between the two variables.
Configure these settings according to your study design and then click .
Do use the standard chi‑square test. For paired data (e.g., each subject measured before and after an intervention, or matched case‑control studies), you need the McNemar test . GraphPad Prism does not include the McNemar test in its main software, but GraphPad offers a free online calculator called QuickCalcs that includes McNemar’s test (search for “GraphPad QuickCalcs McNemar” in your browser). For 2×2 tables, Prism offers both the chi-square
The GraphPad output for the Chi-Square test includes:
: Ensure your data consists of actual counts (frequencies), not percentages or transformed values.
typically indicates a statistically significant difference between observed and expected frequencies. : If your calculated χ2chi squared value exceeds the critical value for your For large samples, the two tests yield nearly
To ensure your results are valid within GraphPad Prism, verify these conditions:
value relative to your degrees of freedom corresponds to a lower P-value. Expected Values Table