##---------------------------------
##  NFL Salaries
##---------------------------------

# Import NFLsalary data
salary = read.csv("http://faculty.chicagobooth.edu/nicholas.polson/teaching/41000/NFLsalary.csv", header = TRUE) 

# attach the dataset 
attach(salary)

# Plot a boxplot to compare salaries of the NFC to AFC.
plot(Conf, Salary, main="Team Salary by Conference", 
     xlab="Conference", ylab="Salary ($1,000s)")

# Dummy coding (dummy code the "Conf" variable into NFC = 1 and AFC = 0)
dConf = as.numeric(Conf) - 1

# Routine analysis
mean(dConf)
sd(dConf)
cor(dConf, Salary)

# Linear regression wit a dummy variable
model = lm(Salary ~ QB + dConf) 
# model = lm(Salary ~ QB + Conf)  #produces the same regression result.
summary(model)

# detach the dataset 
detach(salary)