Death comes to us all. Life's but a walking shadow | Best Statement of the Week!: "According to a recent study, USDA objective yield estimates for corn are biased upwards by about 12 to 15 percent (it is not clear if the statement applies to state or national estimates and the bias is approximately offset by an opposite downward bias in farm operator yield estimates).
Second best statement: "We suspect that most observers would be surprised at either the low confidence levels, low levels of accuracy, or both, implied by the sample sizes used in many (but not all) crop tours. In addition, the accuracy of crop tour estimates may be compromised by non-random sample selection and non-sample measurement errors. In view of these limitations, what can be learned about corn and soybean yields from crop tour estimates? 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."
All that said, if I remember correctly the Profarmer Tour collected all told 1300 samples across seven states or 1300/7= 200 per state. If Ill. needs 355 samples to get within +/- 3.8 bushel (2%) then their Illinios estimate of 196 bu/A might be off 5 bushel or 60 million bushel. A 5 bushel error doesn't change the overall results and it doesn't count for much in relation to the total national production but it does suggest how to explain the problem of "did we run out" at the end of the next year since 60 million bushel is a noticeable amount of the carryout.
Thanks, Scott, 'appreciate the perspective. |
Crop Tours and USDA Forecasts
