Revisiting Surprises in USDA’s Quarterly Grain Stocks Estimates–Evidence from Wheat10/20/2016
A major controversy about USDA grain stocks estimates erupted during the last decade. We found in an earlier study that there had indeed been a sharp decline in analysts’ ability to anticipate actual quarterly corn stock estimates over the 2006-07 through 2012-13 marketing year (Irwin, Sanders, and Good, 2014; farmdoc daily, January 17, 2014; January 29, 2014; February 7, 2014; February 13, 2014; February 14, 2014). However, a similar decline was not found for soybeans, which was one of the reasons that we argued there was nothing inherently amiss with the USDA’s corn stocks estimates. After all, corn and soybean stock estimates are based on the same USDA survey. Instead, we argued that the decline in analysts’ ability to anticipate actual quarterly corn stock estimates for the 2006-07 through 2012-13 marketing years was most likely explained by unusually large and unresolved sampling errors in USDA corn production estimates, particularly for the 2009, 2010, and 2012 crops. We updated the results for corn and soybeans through the 2015-16 marketing year in a recent farmdoc daily article (July 20, 2016), and the updated results confirmed our previous conclusions. In this article, we make use of new data for quarterly wheat stock estimates to provide a fresh comparison to corn and soybeans.