The 58/42 split between above and below trend yields discussed above is a general statement that applies to any year in the sample. A different, but related, question is whether there is a marked correlation between deviations from year-to-year. In other words, is there a tendency towards continuation or reversal of deviations? Figure 3 shows that there is a very small negative correlation (-0.0159) between the yield deviation in the previous year and the current year (correlations can vary between -1 and +1, with zero indicating no relationship). For all practical purposes this correlation is indistinguishable from zero, which means that a negative yield deviation last year does not necessarily tend to be followed by a positive deviation this year and vice versa. Even the very limited tendency is sensitive to just a few years with large negative yield deviations. If 1983, 1988, 1993, and 2012 are deleted from the sample the negative correlation completely disappears.The bottom-line is that there is no systematic tendency for the U.S. average corn yield to increase or decrease based on what happened in the previous year.