Finding Critical t Values When finding critical values, we sometimes need significance levels other than those available in Table 3 of Appendix: Tables. Some computer programs approximate critical t values by calculating

where df = n - 1, e = 2.718, A = z(8 # df + 3)>(8 # df + 1) and z is the critical z score.
Use this approximation to find the critical t score corresponding to n = 150 and a significance level of 0.05 in a right-tailed case.

t= Vdf (e/df-1)