Crop tours generate a lot of attention with their estimates of crop yields or output but the organizers often say little about the level of accuracy they represent. “Our position is that most crop tour estimates provide useful qualitative information about crop prospects (e.g., average, good, bad) but quantitative estimates (e.g., Illinois state average yield of 190 bushels) are not likely to have a high degree of reliability,” write economists Scott Irwin, Darrel Good and Gary Schnitkey of U-Illinois.
In an article on farmdoc daily, they say, given the normal range of yield variability, 355 samples are needed to produce an estimate that is within 2 percent; 57 samples are needed for a margin of error of +/-5 percent. Beyond that, they note the challenge of random sampling and determining the proper factors to convert field data into a crop estimate.