The following code produces a quantile-quantile plot using R.

wta=c(445,530,540,510,570,530,545,545,505,535,450,500,520,460,430,520,520,430,535,535,475,545,420,495,485,570,480,495,470,490) wtb=c(530,540,570,530,545,505,450,500,520,460,430,520,430,535,475,545,420,495,530,570,480,495,470,490,430,420,430,425,440,420) qqplot(wtb,wta,ylim=c(400,600),xlim=c(400,600),main='Quantile-quantile plot',col='blue',ylab='Herd A weights',xlab='Herd B weights',pch=19) abline(a=0,b=1,col='red')

• You can use qqplot to produce a QQ plot of two datasets. This is comparison of two sample distributions - no comparison is being made to any theoretical distribution.

• In this example sample sizes are the same so there is no interpolation. If sample sizes differ, the values of the appropriate quantiles are interpolated.

• If sample sizes are different, equivalent quantiles to those in the smaller sample are interpolated in the larger sample.