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Hypothesis Testing for Diffrence of Dispersion

In Hypothesis Testing for Diffrence of Average , we use difference to compare 2 average. But we use ratio to compare 2 dispersion.

Standard deviation is popular as the index of dispersion. But we use variance to compare dispersion.

Hypothesis Testing for 2 Variance

F-test is used to compare 2 variance.

Calculation by R

setwd("C:/Rtest")
Data <- read.csv("Data.csv", header=T)
var.test(x=Data$X1,y=Data$X2)

Hypothesis Testing for More Than 2 Variance

Bartlett-test is used.

This method is used to check equality of variance before ANOVA .

Quality Engineering analyze the difference of dispersion. But it is not hypothesis testing.

Calculation by R

setwd("C:/Rtest")
Data <- read.csv("Data.csv", header=T)
bartlett.test(formula=Data$Y~Data$X)




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