# Some useful commands for the project
################################
# Save the data set bed.txt in a directory, say, your A drive
# Open R
# Do ``change directory'' in R to A drive. This is Important!!!
# (To ``change directory'', click on File, you will see the change
# directory button.
# Input lowbwt data
bed <- read.table("bed.txt",header=T, sep="\t",quote="", skip=0,
         row.names=NULL)
#######################

bed80 <- bed[[1]]
bed86 <- bed[[2]]

#### Boxplots
boxplot(bed80, bed86)

#### Boxplots: putting on the lables
boxplot(bed80, bed86, axes=F)
box()
axis(side=2, at=3:7)
axis(side=1, at=1:2, labels=c("bed80", "bed86"))
title(main="Boxplots of bed data in 1980 and 1986")
#### Histograms
par(mfrow=c(2,1))
hist(bed80, probability=T)
hist(bed86, probability=T)

### Scatter plot
plot(bed80, bed86)

### paried t-test
t.test(bed80-bed86)

### two-sample t-test: compare bed80 and bed86
t.test(bed80, bed86)

### two sample t-test: compare the first 24 states 
### and the remaining 27 states
bed86.1 <- bed86[1:24]
bed86.2 <- bed86[25:51]
t.test(bed86.1, bed86.2)