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arXiv 0908.3428math.STstat.TH
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正态混合模型的假设检验:EM方法

Hypothesis test for normal mixture models: The EM approach

Jiahua Chen, Pengfei Li

摘要:

正态混合分布可以说是最重要的混合模型,也是最具技术挑战性的。基于一组随机样本,正态混合模型的似然函数是无界的,除非在其分量方差参数上设置人工界限。此外,该模型不是强可识别的,因此很难区分由混合物的存在引起的过度分散和由大方差引起的过度分散,并且它具有关于混合比例的无限Fisher信息。对有限正态混合模型的研究已经很多,但大多数研究仅仅是解决点估计的一致性问题或实用的方法,而且许多结果需要对参数空间进行限制。我们表明,EM检验的均匀性是有效的,在有限的正常混合物的背景下,克服了许多挑战。我们发现EM检验的极限分布是一个简单的函数的$0.5χ^2_0+0.5χ^2_1$和$χ^2_1$分布时的混合方差是相等的,但未知的和$χ^2_2$时的方差是不相等的和未知的。模拟结果表明,极限分布能很好地逼近有限样本分布。两个遗传的例子来说明EM测试的应用。

英文摘要:

Normal mixture distributions are arguably the most important mixture models, and also the most technically challenging. The likelihood function of the normal mixture model is unbounded based on a set of random samples, unless an artificial bound is placed on its component variance parameter. Moreover, the model is not strongly identifiable so it is hard to differentiate between over dispersion caused by the presence of a mixture and that caused by a large variance, and it has infinite Fisher information with respect to mixing proportions. There has been extensive research on finite normal mixture models, but much of it addresses merely consistency of the point estimation or useful practical procedures, and many results require undesirable restrictions on the parameter space. We show that an EM-test for homogeneity is effective at overcoming many challenges in the context of finite normal mixtures. We find that the limiting distribution of the EM-test is a simple function of the $0.5χ^2_0+0.5χ^2_1$ and $χ^2_1$ distributions when the mixing variances are equal but unknown and the $χ^2_2$ when variances are unequal and unknown. Simulations show that the limiting distributions approximate the finite sample distribution satisfactorily. Two genetic examples are used to illustrate the application of the EM-test.

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