Type of distributions

Most classical statistical tests assume that the data is normally distributed, ie its histogram or density curve is bell shaped with peak at center. 

code: 

> hist(bwdf$age)

output (graph): 

 

               

code: 

          > plot(density(bwdf$age))

output (graph): 

               

Following function plots 4 graphs which indicate whether the data is normally distributed or not: 

code:

> myqq = function(vect) {
             par(mfrow=c(2,2))
             qqnorm(vect); qqline(vect)
             plot(ecdf(vect), main = 'Cumulative Distribution Curve\n(sigmoid shape means normal distribution)')
 # cumulative distribution; 
            hist(vect)
            plot(density(vect))
}
 > myqq(birthwt$age)

output (graph): 

              
 
 


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