Yang, Seung-Ryong

By: Yang, Seung-Ryong; Koo, Won W.
A source differentiated AIDS model is specified to estimate Japanese meat import demand. Block separability and product aggregation are rejected at conventional levels of significance. The model with the block substitutability restriction explains more than 95% of data variation. The empirical results indicate that the U.S. has the largest potential for beef exports to Japan. Taiwan is in a strong position in the pork market, and Thailand and China are strong in the poultry market. The U.S. competes with Canada and Taiwan in the pork market, but the competition between Taiwan and European countries is the strongest in the market. The U.S. competes with Thailand in the poultry market, where the U.S. is the most vulnerable.
By: Yang, Seung-Ryong; Koo, Won W.; Wilson, William W.
This study examines three alternative models of correcting for heteroskedasticity in wheat yield: the time trend variance, the GARCH, and an econometric model that includes the potential sources of heteroskedasticity. Nonnested test results suggest that modeling the sources of heteroskedasticity is the preferred procedure. Including potential sources of heteroskedasticity as explanatory variables removed the heteroskedasticity in the sample wheat yields. The results also suggest that the GARCH specification is a promising model of correcting for heteroskedasticity when the sources cannot be identified. The time trend variance model alone may misspecify the true variance structure.