Variance

Some statistical test assume the variance of the different data sets are similar. Box plots are an easy graphical method to evulavte the variance. For example below:

  • A-1, A-2, and A-3 appear to be from the same population.

  • D-1 appears to be from a different population but has a similar variance as the A groups.

  • B-1 appears to be from the same population as the A samples but a much larger variance.

  • C-1 appears to be from a different variance and from a different population.

library(car)

setwd("c:/R")

mydata<- read.table("VarianceExampleAll.csv", header=TRUE, sep=",",)

leveneTest(EMD ~ Well, data=mydata)

mydata<- read.table("VarianceExampleSame.csv", header=TRUE, sep=",",)

leveneTest(EMD ~ Well, data=mydata)

plot(mydata, notch=TRUE)

mydata<- read.table("VarianceExampled1.csv", header=TRUE, sep=",",)

leveneTest(EMD ~ Well, data=mydata)

plot(mydata, notch=TRUE)