statistics-skewed data

参考文献：

http://www.statisticshowto.com/skewed-distribution/

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left/negatively-skewed distributions ：

• boxplot：The left whisker will also be longer than the right whisker.

right/positively-skewed distributions

• the right whisker will be longer.

注意：median未必一定在mean和mode之间

对于too skewed的数据，如果需要进行参数检验（比如ANOVA），就需要用log变换，让它没那么skewed。

何时这么做？？

• Your data is highly skewed to the right (i.e. in the positive direction).
• The residual’s standard deviation is proportional to your fitted values
• The data’s relationship is close to exponential.
• You think the residuals reflect multiplicative errors that have accumulated during each step of the computation.