A serious, drought-related problem for farmers is the spread of aflatoxin, a highly toxic substance caused by mold, which contaminates field corn. In higher levels of contamination, aflatoxin is potentially hazardous to animal and possibly human health. (Officials of the FDA have set a maximum limit of 20 parts per billion aflatoxin as safe for interstate marketing.) Three sprays, A, B, and C, have been developed to control aflatoxin in field corn. To determine whether differences exist among the sprays, 10 ears of corn are randomly chosen from a contaminated corn field and each is divided into three pieces of equal size. The sprays are then randomly assigned to the pieces for each ear of corn, thus setting up a randomized block design. The table gives the amount (in parts per billion) of aflatoxin present in the corn samples after spraying. Use the Friedman test to determine whether there are differences among the probability distributions of the amounts of aflatoxin present for the three sprays. Test at the α = .05 level of significance.

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AFLATOXIN Spray B Spray B Ear A Ear A 21 23 15 5 12 6. 2 29 30 21 7 18 18 12 3 16 19 18 8 26 32 21 4 20 19 18 17 20 9. 13 10 14 10 4 10 2 1.