63. The critical ick er frequency (cff) is the highest frequency

(in cycles/sec) at which a person can detect the ick er in a ick ering light source. At frequencies above the cff, the light source appears to be continuous even though it is actually ick ering. An investigation carried out to see whether true average cff depends on iris color yielded the following data

(based on the article The Ef fects of Iris Color on Critical Flicker Frequency, J. Gen. Psych., 1973:

91—95):

Iris Color 1. Brown 2. Green 3. Blue 26.8 26.4 25.7 27.9 24.2 27.2 23.7 28.0 29.9 25.0 26.9 28.5 26.3 29.1 29.4 24.8 28.3 25.7 24.5 Ji 8 5 6 204.7 134.6 169.0 25.59 26.92 28.17 n  19

a. State and test the relevant hypotheses at signi cance level .05 by using theFtable to obtain an upper and/or lower bound on the P-value. (Hint:

and CF13,598.36.)

b. Investigate differences between iris colors with respect to mean cff.