Question

Consider the ToothGrowth data in R, concerning the Effect of Vitamin C on Tooth Growth in Guinea Pigs. :

1.Ignore ‘dose’ and determine whether there is a significant difference in the mean “len” between the two groups (i.e., OJ vs VC):

a)A parametric procedure

b)A non-parametric procedure

Discuss the assumption underlying each of the analyses, their validity, and any remedial measures to be taken.

Answer 1

a)

library(datasets)
data("ToothGrowth")

VC <- subset(ToothGrowth, supp == "VC", select = c("len"))
OJ <- subset(ToothGrowth, supp == "OJ", select = c("len"))

t.test(VC,OC, alternative = "two.sided", mu = 0, paired = FALSE, var.equal = FALSE,conf.level = 0.95)

Welch Two Sample t-test

data: VC and OJ
t = -1.9153, df = 55.309, p-value = 0.06063
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-7.5710156 0.1710156
sample estimates:
mean of x mean of y
16.96333 20.66333

p-value = 0.06063 > 0.05

we fail to reject the null hypothesis

there is no significant difference in the mean “len” between the two groups