The critical flicker frequency (cff) is the highest frequency (in cycles/sec) at which a person can detect the flicker in a flickering light source. At frequencies above the cff, the light source appears to be continuous even though it is actually flickering. An investigation carried out to see whether true average cff depends on iris color yielded the following data (based on the article "The Effects of Iris Color on Critical Flicker Frequency," J. of General Psych., 1973: 91–95): Iris colour
Brown Green Blue
26.8 26.4 25.7
27.9 24.2 27.2
23.7 28.0 29.9
25 26.9 28.5
26.3 29.1 29.4
24.8 28.3
25.7
24.5
Ji 8 5 6
Xi 204.7 134.6 169.0
xi 25.59 26.92 28.17
n=18 x=508.3
a. State and test the relevant hypotheses at significance level .05
b. Investigate differences between