U.S. Soybean Yields: Estimation and Forecasting with Nonsymmetric Disturbances
研究发现美国全国平均大豆产量分布呈左偏态，低产概率较高；最大似然估计支持这一假设，修正后的预测值高于基于对称分布的预测，且产量不稳定性持续上升。
National average soybean yields are skewed with a relatively high chance of low yields. Maximum likelihood estimates support this hypothesis. Revised forecasts which account for skewed yields are positioned higher than forecasts based on the illusion of a symmetric distribution. Also, yield instability has been increasing steadily; the standard deviation of the soybean yield distribution is twenty‐five percent higher in the late 1980s than it was in the early 1970s.