Opening Up the Black Box: More on the USDA Corn Yield Forecasting Methodology

Abstract

We have written extensively about U.S. corn yield forecasts issued by the National Agricultural Statistics Service (NASS) of the USDA (Irwin and Good, 2006; Irwin and Good, 2011; Irwin, Sanders and Good, 2014; farmdoc daily, August 28, 2013; August 29, 2014; August 18, 2016). As indicated in these previous publications, NASS uses two surveys to provide indicators of corn yield prior to harvest. These include the Agricultural Yield Survey (or farmer-reported survey) and the Objective Yield Survey (or fieldmeasurement survey) in major corn producing states. A formal Agricultural Statistics Board (ASB) of NASS statisticians is convened in each month of the forecasting cycle to review yield indicators and determine an official yield forecast. In our previous publications we focused on the survey procedures used by NASS and had relatively little to say about the methodology used by the ASB to combine the various yield indicators and determine an official yield forecast. This omission reflects the fact that NASS has historically provided very little information about this part of the forecasting methodology. Fortunately, several publications have appeared in the scientific literature during the last several years that provide important insights into the nature of the different survey yield indications and the other nonsurvey information used by the ASB to determine official published yield forecasts. The purpose of this article is to review the information in these scientific articles and provide a more informed understanding of the role of the ASB in generating these important market-moving forecasts.