Wednesday, October 7, 2009

How does the USDA change its estimates through the year?

  • I've historically done a comparison piece where I compare my own errors in predicting final yields (in sample) to USDA's own errors (out of sample of course) to compare the relative accuracy and to see how errors decline throughout the growing season. I haven't done this for my own model yet (this is supposed to be a hobby) but I'll try to get some assistance in posting them but in the mean time, below you will find the USDA error distribution for corn and soybeans from 1986. The error I'm talking about here is each months guess relative to the final yield estimate. So for August, it is (August estimate-final). The blue dot is the average error while the red dot is plus/minus one standard deviation. From this you can really see that the movements from November are normally quite small, but there is still significant movement from October to the final estimate.
  • I'm farther away from the USDA estimates than 'normal' at this time of the year. It could be lots of things such as changes in technology, a oversized penalty for late planting based to much on history which no longer applies, some yet unknown error?

    Not that I expect that I'll end up closer to USDA but I can hope. USDA could just as easily move further away from me on the upside for corn, or the downside for beans, but I'm given some hope by the recent corn and bean price movements that maybe on Friday I'll be a bit closer to USDA. I'll try to post those errors of my own work tomorrow and after the Friday report I'll give a state by state breakdown of how I compare. Email me if there is something else you want to see with respect to the errors. I've got some assistance in putting this all together so I can certainly promise somebody else's time to make it happen.

    US Corn

    US Soybean

    Illinois Corn

    Iowa Corn

    Indiana Corn

    Nebraska Corn

    Minnesota Corn

    Missouri Corn

    Ohio Corn

    Illinois Soybean
    Iowa Soybean

    Indiana Soybean

    Nebraska Soybean

    Missouri Soybean

    Minnesota Soybean

    Ohio Soybean

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