Using Models to Estimate Hog and Pig Inventories Proceedings of a Workshop (2019) / Chapter Skim
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5 Modeling Efforts
5 Modeling Efforts
Pages 27-36
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From page 27... ...
PURPOSES OF A MODEL As context, he said, the purpose of a hog inventory model is to produce estimates for the hog inventory categories described in earlier chapters. For purposes of evaluation, NASS compares the model estimates to the initial official estimate released by the Hog Board.
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The current state depends on the state in the past five quarters to capture cycle dynamics and annual trends. The measurement or observation equation describes how the measurements (e.g., survey data)
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It tracked the initial estimate fairly closely, had some trouble coming out of the shock, then started tracking reasonably well and relatively quickly. Figure 5-2 plots the differences between the final estimate for total hogs and the KFM (blue)
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They included additional variables from which to select, including economic variables such as pork price. Kedem and Pan used survey results, board estimates, and differences in revisions.
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FIGURE 5-2 Difference between initial and Kalman filter model estimates with final estimates. SOURCE: Prepared by Gavin Corral for presentation at the workshop.
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FIGURE 5-4 Difference between initial and sequential generalized linear model estimates with final estimates. SOURCE: Prepared by Gavin Corral for presentation at the workshop.
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Corral said NASS hopes that the model described in Chapter 7 makes progress toward meeting the four criteria that he set forth earlier in this chapter. DETECTING DISRUPTIONS Corral briefly described a third, new model to identify shocks developed by Wang and colleagues (2019)
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Chris Wikle asked about the number of free parameters in the KFM and whether they are estimated in every run. Corral replied that parameters are estimated in every run, with perhaps six or seven parameters estimated in each run.
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With new data streams, covariates from other sources could also be used. Katherine Ensor commented NASS basically has two state-space models with different formulations.
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