How to calculate p value between 2 boxplots?
I plotted boxplots using the following commands. Is there any way to calculate the statistical significance (pvalue) between boxplot1 vs boxplot2 and 3 vs 4 and also add the value in between 2 boxplots by connecting them ?

    data(mtcars)
    qplot(factor(cyl), mpg, data = mtcars, geom = "boxplot") 
How to calculate p value between 2 boxplots?
===

I plotted boxplots using the following commands. Is there any way to calculate the statistical significance (pvalue) between boxplot1 vs boxplot2 and 3 vs 4 and also add the value in between 2 boxplots by connecting them ?

    data(mtcars)
    qplot(factor(cyl), mpg, data = mtcars, geom = "boxplot") 