Multiple curvilinear regression analysis has been used to separate the effects of weather from the effects of technology on the trend in corn yields in Illinois, Indiana, Iowa, Missouri and Ohio. These five states produce about half the corn produced. in the United States.

The weather during the four-Year period 1958-1961 was unusually favorable for corn in the five states under study. Had trend yield.s been realized during 1958, 1959 and 1960, these five states would have produced about 93 percent as much corn as was actually produced. The additional amount of corn produced because of favorable weather was approximately equal to that added to storage during 1958, 1959 and 1960 from these states.