diarrhea <- read.delim("http://myweb.uiowa.edu/pbreheny/161/data/diarrhea.txt")
attach(diarrhea)
View(diarrhea)

boxplot(Stool~Group,col="gray")

require(lattice)
histogram(~Stool|Group)

source("http://bit.ly/HzbVt3")
error.bar(Stool,Group)

#Show histograms are mean of each group
mean(Stool[Group=="Control"])
mean(Stool[Group=="Treatment"])

source("http://bit.ly/HzbVt3")
error.bar(Stool,Group,conf.level=.8)
error.bar(Stool,Group,bar="SE")
error.bar(Stool,Group,bar="SD")



t.test(Stool~Group,var.equal=TRUE) ## Student's
t.test(Stool~Group) ## Welch's

## PRACTICE PROBLEM
detach(diarrhea)
infantheart <- read.delim("http://myweb.uiowa.edu/pbreheny/161/data/infantheart.txt")
attach(infantheart)
View(infantheart)

##A
arrest <- infantheart[Treatment == "Circulatory arrest",]
low <- infantheart[Treatment == "Low-flow bypass",]
sd(arrest$PDI)
sd(arrest$MDI)
sd(low$PDI)
sd(low$MDI)

##B
t.test(PDI~Treatment,var.equal=TRUE)

##C & D
t.test(MDI~Treatment,var.equal=TRUE)