7. Critical r value In order for there to be evidence of a non-zero correlation coefficient in the population, an observed r value in a sample must be larger than the critical r value found in Table B6. In addition to alpha and the number of tails for the test, you also need the degrees of freedom for the test. In general, what is the df value equal to for the Pearson r hypothesis test? n-1 (n-1) (n-1) n-2