Identify the statistical method or test being used
Determine the sample size or number of observations
Count the number of independent values that can vary
Subtract any estimated parameters, constraints, or fixed totals
Use the appropriate formula for the situation
For a single sample, use n – 1
For two independent samples, use n1 + n2 – 2
For a chi-square contingency table, use (rows – 1)(columns – 1)
For regression, use n – p – 1
Verify the result matches the test or model requirements