Introduction: County level yield data reveal a trend as time increases so the data should be detrended. The purpose is to account for systematic changes in yield levels over time. Other sources of yield variance, like soil type, improved varieties, and increased soil fertility are assumed to be either constant or captured by this detrending process (Cao, 2004). Following Woodard and Garcia (2007), yields are detrended using a simple linear trend model in the tool.
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