The degrees of freedom (df) for a Chi-Square test of independence is determined based on the number of categories in the contingency table you’re working with. Specifically, the formula to calculate the degrees of freedom is:
df = (r – 1) * (c – 1)
In this formula, r represents the number of rows in the contingency table, and c represents the number of columns.
For example, if you have a 2×3 contingency table (2 rows and 3 columns), you would calculate the degrees of freedom as follows:
- r = 2
- c = 3
Now plug these values into the formula:
df = (2 – 1) * (3 – 1) = 1 * 2 = 2
This means that for a 2×3 contingency table, you have 2 degrees of freedom.
Understanding how to find the degrees of freedom is crucial because it helps determine the critical value from the Chi-Square distribution needed to interpret your test results effectively.