The appropriate critical value can be found in a table of probabilities for the F distribution(see "Other Resources"). In order to determine the critical value of F we need degrees of freedom, df1=k-1 and df2=N-k. In this example, df1=k-1=4-1=3 and df2=N-k=20-4=16. The critical value is 3.24 and the decision rule is as follows: Reject H0 if F > 3.24.