Friday, 7 September 2018

Statistical Function-Boxplots, Skewness and Kurtosis in R Language

Summary of observation

In R, quartiles, minimum and maximum values can be easily obtained by the summary command

summary (x)    x: data vector
It gives information on
  • minimum
  • maximum
  • first quartile
  • second quartile (median) and
  • third quartile.

Boxplot

Boxplot is a graph which summarizes the distribution of a variable by using its median, quartiles, minimum and maximum values.



boxplot ( ) draws a box plot





Descriptive Statistics:

First hand tools which gives first hand information.
  • Structure and shape of data tendency (symmetricity, skewness, kurtosis etc.)
  • Relationship study (correlation coefficient, rank correlation, correlation ratio, regression etc.)

Skewness

Measures the shift of the hump of frequency curve.
Coefficient of skewness based on values x1,x2,....,xn.






Kurtosis

Measures the peakedness of the frequency curve.
Coefficient of kurtosis based on values x1,x2,...,xn.





Skewness and Kurtosis

First we need to install a package 'moments'
> install.packages ("moments")
> library (moments)
skewness  ( )  :  computes coefficient of skewness
kurtosis    ( )   :  computes coefficient of kurtosis



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