线性模型是一类很重要的统计模型，它包括回归模型、方差分析模型、协方差分析模型以及混合模型等。

Linear model is a vital class of statistical model which involves regression model, variance analysis model, covariance analysis model and mixed model etc.

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结论：在协方差分析中使用哑变量使对模型的理解变的简单，在方差分析中使用哑变量使得可以从回归的角度来理解模型。

Conclusion: It is easy to understand the analysis of covariance and analysis of variance can also be considered in regression analysis setting by defining appropriate dummy variables.

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遗传协方差分析结果表明，5个重金属元素含量间的基因型协方差均为正向。

Analysis on genetic covariance proved that genotype covariance was detected to be positive between these 5 heavy metal contents.

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