被样本回归直线解释,有27%未被解释,因此,样本回归直线对样本的拟合优度不是很高的。给出显著水平α=0.05,查自由度v=21-2=19的t分布,得临界值t0.025(19)=2.09,T0=-3.93<t0.025(19)=2.09,t1=7.17>t0.025(19)=2.09,故回归系数均显著不为零,回归模型中应包含常数项,X2t对Qt有显著影响。(3)用其中最好的模型求预测值。由上述分析可知,X2t预测的最准确,假定1999年,2000年,2001年,2002年化肥施用量分别为4190.8万吨,4287.5万吨,4367.9万吨,4495.7万吨,预测值分别为65452.97万吨,66963.25万吨,68218.36万吨,70214.97万吨。25,00030,00035,00040,00045,00050,00055,00060,00078808284868890929496980002QF±2S.E.Forecast:QFActual:QForecastsample:19782002Includedobservations:21Root Mean Squared Error 1507.277Mean Absolute Error 1129.227Mean Abs. Percent Error 2.903414Theil Inequality Coefficient 0.018198 Bias Proportion 0.000000 Variance Proportion 0.016736 Covariance Proportion 0.9832642000年的预测区间为:[66963.25-2.09×2657.32,66963.25+2.09×2657.32]计算得:[61409.45,72517.05]
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