Finding Lower Critical F Values For hypothesis tests that are two-tailed, the methods of Part 1 require that we need to find only the upper critical value. Let’s denote the upper critical value by FR, where the subscript indicates the critical value for the right tail. The lower critical value FL (for the left tail) can be found as follows: (1) Interchange the degrees of freedom used for finding FR; (2) then, using the degrees of freedom found in Step 1, find the F value from Table A-5; (3) take the reciprocal of the F value found in Step 2, and the result is FL. Find the critical values FL and FR for Exercise 16 “Blanking Out on Tests.”