# Fisher's Exact Test

## Fisher's Exact test is used when the chi-square assumption is violated

Fisher's Exact Test is very similar to the chi-square test in that researchers are testing the

Fisher's Exact Test is often used with

SPSS automatically calculates a Fisher's Exact Test

**association or relationship between two dichotomous categorical variables**. The primary difference between the two is that Fisher's Exact Test is used ONLY when**one of the four cells of a 2x2 table has less than five observations**.Fisher's Exact Test is often used with

**small sample sizes**(n < 20) and when researching**rare outcomes**. The*p*-value is not interpreted with Fisher's Exact Test. The unadjusted odds ratio with 95% confidence interval is used instead. The width of the 95% confidence interval will be extremely wide due to the limited number of observations in one of the four cells.SPSS automatically calculates a Fisher's Exact Test

*p*-value when conducting chi-square analysis.Fisher's Exact Test is used when any cell of the 2x2 table has less than five observations.

### The steps for conducting a Fisher's Exact Test in SPSS

1. The data is entered in a between-subjects fashion. The control group is codified as "0" and the treatment group is codified as "1." Absence of the outcome is codified as "0" and presence of the outcome is codified as "1."

2. Click

3. Drag the cursor over the

4. Click

5. Click on the dichotomous categorical predictor variable to highlight it.

6. Click on the

7. Click on the dichotomous categorical outcome variable to highlight it.

8. Click on the

9. Click on the

10. Click on the

11. Click on the

12. Click

13. Click

2. Click

**.**__A__nalyze3. Drag the cursor over the

**D**drop-down menu.__e__scriptive Statistics4. Click

**.**__C__rosstabs5. Click on the dichotomous categorical predictor variable to highlight it.

6. Click on the

**arrow**button to move the variable into the**R**box.__o__w(s):7. Click on the dichotomous categorical outcome variable to highlight it.

8. Click on the

**arrow**button to move the variable into the**box.**__C__olumn(s):9. Click on the

**button.**__S__tatistics10. Click on the

**C**box to select it.__h__i-square11. Click on the

**R**box to select it.__i__sk12. Click

**Continue**.13. Click

**OK**.### The steps for interpreting the SPSS output for Fisher's Exact Test

1. Look at the

2. Interpret the

3. If researchers have a significant

If the

If the

If the

**Crosstabulation**table. This table shows the dispersal of the predictor variable across levels of the outcome variable.2. Interpret the

**Fisher's Exact Test Exact Sig. (2-sided)***p*-value.3. If researchers have a significant

*p*-value, then they can interpret the first row in the**Risk Estimate**table. The unadjusted odds ratio is presented in the**Value**column and the**lower**and**upper**limits of the 95% confidence interval wrapped around the odds ratio.If the

*p*-value is significant and the odds ratio is above 1.0 along with the confidence interval, then the treatment group is**MORE LIKELY**to have the outcome.If the

*p*-value is significant and the odds ratio is below 1.0 along with the confidence interval, then the treatment group is**LESS LIKELY**to have the outcome.If the

*p*-value is non-significant, then researchers will see that the 95% confidence interval**crosses over 1.0**. They can report the odds ratio or*p*-value as needed.Click on the

**Download Database**and**Download Data Dictionary**buttons for a configured database and data dictionary for Fisher's Exact test.**Click on the****Validation of Statistical Findings**button to learn more about bootstrap, split-group, and jack-knife validation methods.## Hire A Statistician

**DO YOU NEED TO HIRE A STATISTICIAN?**

Eric Heidel, Ph.D., PStat** **will provide the following statistical consulting services for undergraduate and graduate students at $100/hour. Secure checkout is available with Stripe, Venmo, Zelle, or PayPal.

- Statistical Analysis
- Research Design
- Sample Size Calculations
- Diagnostic Testing and Epidemiological Calculations
- Survey Design and Psychometrics