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====== The shape of frequency distribution ======

===== Symmetrical distribution =====

  *Definition: A distribution in which the frequency of values above the mean are a mirror image of those below the mean. 

===== Skewed distribution =====
((APA词典中并无该词，与之相应的词条有“skewness distribution”。))

  *Definition: Data is piled up at one end of the distribution, and the other end becomes the thinner tail.

==== Positively skewed ====

  *As shown in the left figure, the data is stacked on the left and tailed on the right. Its tail is pointed to the positive end of the X-axis, and here came the name positive skewed distribution. It has a higher mean than median.

==== Negatively skewed ====

  *As shown in the figure on the right, if the data is stacked on the right and the tail is on the left, the distribution is so called negatively skewed. It has a lower mean than median.
    *//For more information,please check for the part of [[分布的形状与集中量数|numbers of concentrations]].//
{{ :偏态分布.png?400 | }}
  *The skewed distribution reflects the asymmetry of the data. So some special methods should adopted when processing, such as logarithmic transformation, Box-Cox transformation, etc.

==== Bimodal distribution ====

  *Definition:There are two distinct peaks or high-frequency regions in the data distribution, which means the number of times is concentrated in two fractions, resulting in two raised peaks in the distribution curve.
{{ :双峰分布.png?400 | }}

==== Rectangle distribution ====

  *Definition: All values in a distribution are of the same frequency.
{{ :矩形分布.png?400 | }}