Finding Critical Values In constructing confidence intervals for s or s2, Table 4 in Appendix: Tables can be used to find the critical values x2 L and x2 R only for select values of n up to 101, so the number of degrees of freedom is 100 or smaller. For larger numbers of degrees of freedom, we can approximate x2 L and x2 R by using

where k is the number of degrees of freedom and za/2 is the critical z score described in Section 2.

Use this approximation to find the critical values x2 L and x2 R for Exercise 9.

How do the results compare to the actual critical values of 82.354 and 129.918?

x [za/2 + 2k - 1]