Death comes to us all. Life's but a walking shadow | Kevin, Did you read the reference you cited? It is very interesting because it only confirms my previous analysis of the USDA forcasts, namely the strategy they use is not the best. They make a new forcast each time instead of including the new information into the old. They essentially throw away previous information. You wouldn't do that. If you made sequential yield estimates over time you wouldn't discard the early ones because by including them in a weighted ave you would reduce the noise.
Second, the formula they use to calculate error disregards sign of the error and thereby doesn't detect systematic error. They in effect throw away more valuable information about their methods namely that they are biased. We already suspect that their methods systematically overestimate the yield. They don't seem to understand the basic difference between accuracy and reproducibility. For example you can shoot three shots from a rifle at a target and have a close group butstill miss the bullseye by a substantial amount. In their case they never measure by how much they miss the bullseye.
In addition they themselves say:
"Egelkraut et al. (2003), offer this suggestion:
"The improved performance by the private agencies for August for both crops during the most recent years, and the ability of the private agencies to generate relatively accurate forecasts in soybeans suggest that it might be useful for USDA to investigate expanding the scope of their subjective yield analysis to incorporate a wider range of market and industry participants. Such a strategy, if proved effective, might lead to improved crop production forecasts." (p. 94)"
And
"As a final point, it is interesting to consider the results of other studies that compare the forecasting accuracy of public agencies and private firms. Just and Rausser (1981) compare internal USDA agricultural price forecasts to price forecasts from four private firms (and futures markets) over December 1976-December 1978. They report that, on average, USDA forecasts of wheat, corn, soybean, soybean meal, soybean oil, cotton, hog and cattle prices are less accurate than comparable forecasts from each of the four private firms."
I could go on but it is quite late. |
For the conspiracy theorists
