15.41 Toxic Chemicals An experiment was EX1541 conducted to compare the effects of three toxic chemicals, A, B, and C, on the skin of rats. One- centimetre squares of skin were treated with the chemicals and then scored from 0 to 10 depending on the degree of irritation. Three adjacent 1-centimetre squares were marked on the backs of eight rats, and each of the three chemicals was applied to each rat. Thus, the experiment was blocked on rats to eliminate the variation in skin sensitivity from rat to rat.

a. Do the data provide sufficient evidence to indicate a difference in the toxic effects of the three chemi- cals? Test using the Friedman F, test with a = 0.05.

b. Find the approximate p-value for the test and inter- pret it.

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Rats 1 2 3 4 5 B 5 AGUM 6 AGC4 9 46 A C B 6 8 9 95 B 9 BB C A 8 8 5 C 3 80 B 9 3 03 C AS A A 5 7 B7 B 7 7 95 B 80 7 A& 8 B 7 AG C 7