求助：卡方检验和对数似然比的区别

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yuliaoku

初级会员
在WordSmith Tool的KeyWord工具中提供了两种计算结果，一种是卡方，另一种是对数似然比。但是，这两种结果都可以用3.84, p<0.05这个标准来检验差异的显著性。请高手指点一下，在使用上有什么区别吗？

先谢了！
 
回复: 求助：卡方检验和对数似然比的区别

急用，烦请知道者作答。
再次表示感谢！
 
回复: 求助：卡方检验和对数似然比的区别

这两天一直在关注对这个帖子的回复。
先感谢Volfer的及时回复，至少我知道了LL更精确一些。但是，这样的答复会引出我的另一个问题，既然卡方不太准确，而LL更精确，为什么还有很多人在使用卡方而不使用LL Ratio? 这两种方法是否在使用上有所偏重，比如相互对比的两个语料库的大小等？
只是想彻底搞搞清楚，所以还得继续请C友帮忙。谢啦！
 
回复: 求助：卡方检验和对数似然比的区别

我想LL Ratio相对卡方更精确并不意味着卡方就不准确，对不对？
卡方得以广泛运用的原因有很多，如SPSS的大量推广等等。
 
回复: 求助：卡方检验和对数似然比的区别

Roughly speaking, log likelihood is seen as an improved type of significance test of chi-squared. They are inherently related in terms of data type and data distribution.

They are both accepted as good methods for significance test.

But chi-square test does not work well with frequency less than 5, LL does. Moreover, chi-square score changes drastically with very big corpus size.

Actually, frequency less than 5 will not good data anyway. That's to say, the 3-4 occurrences might be due to chance. In this case, some statisticians propose fisher exact test to deal with data less than five. I personally don't buy it.
 
回复: 求助：卡方检验和对数似然比的区别

作者 xujiajin:
Roughly speaking, log likelihood is seen as an improved type of significance test of chi-squared. They are inherently related in terms of data type and data distribution.

They are both accepted as good methods for significance test.

But chi-square test does not work well with frequency less than 5, LL does. Moreover, chi-square score changes drastically with very big corpus size.

Actually, frequency less than 5 will not good data anyway. That's to say, the 3-4 occurrences might be due to chance. In this case, some statisticians propose fisher exact test to deal with data less than five. I personally don't buy it.
Click to expand...

受教了^_^
 
回复: 求助：卡方检验和对数似然比的区别

谢谢许博，也谢谢Volfer。这样就有了一个比较准确的说法了。
此外，有人说LL适用于两个规模差别较大的语料库中数据差异显著性检验（如一个库8万词，另一个库80万词），而卡方则不适用，有这样的说法吗？因为本人数学较差，不会去推导原来的公式，因此只想知道使用方面应该注意的问题就够了。
还麻烦许博作答。非常非常感谢！
 
回复: 求助：卡方检验和对数似然比的区别

Yes. You are right. When two corpora differ greatly in size, the chi-square value goes extremely high.
 
回复: 求助：卡方检验和对数似然比的区别

谢谢许博！
这样我对这个问题就有了一个比较全面的了解了。
再说一声谢谢！
 
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