An alternative to using Table A–9 to find critical values for rank correlation is to compute them using this approximation:

Here, t is the critical t value from Table A-3 corresponding to the desired significance level and n - 2 degrees of freedom. Use this approximation to find critical values of rs for Exercise 15 “Blood Pressure.” How do the resulting critical values compare to the critical values that would be found by using Formula 13-1 on page 633?