Aphid infestation of fruit trees can be controlled either by spraying with pesticide or by inundation with ladybugs. In a particular area, four different groves of fruit trees are selected for experimentation. The first three groves are sprayed with pesticides 1, 2, and 3, respectively, and the fourth is treated with ladybugs, with the following results on yield:

ni Number xi Treatment of Trees (Bushels/Tree) si 1 100 10.5 1.5 2 90 10.0 1.3 3 100 10.1 1.8 4 120 10.7 1.6 Let i
the true average yield (bushels/tree) after receiving the ith treatment. Then



1 3

(1 2 3)  4 measures the difference in true average yields between treatment with pesticides and treatment with ladybugs. When n1,