# R-program for Supplementary Exercises 7.102 and 7.103 of IPS7e

lessons <- read.csv("r:/Chapter 7/ex07_102.csv")
lessons$change <- lessons$r

# 7.102
stem(lessons$change[lessons$g==0])
stem(lessons$change[lessons$g==1])

summary(lessons$change[lessons$g==0])
summary(lessons$change[lessons$g==1])
# manual calculation of the standard errors
sd(lessons$change[lessons$g==0])/sqrt(length(lessons$change[lessons$g==0]))
sd(lessons$change[lessons$g==1])/sqrt(length(lessons$change[lessons$g==1]))
# alternatively, use doBy library

# normality checks in the two groups
shapiro.test(lessons$change[lessons$g==0])
shapiro.test(lessons$change[lessons$g==1])

t.test(change~group, data=lessons)
# if we want to assume equal variances (which we usually don't do):
t.test(change~group, data=lessons, var.equal=T)

# 7.103
t.test(change~group, data=lessons, conf.level=0.95)