# Unit 4 for R
# 030521 prepared by C. Andy Tsao

# Q1: Is it reasonable to assume X_1, ..., X_n iid N(mu, sigma)?
# A:  1. Prior information, previous studies
#     2. Cannot do much when n is small
#     3. When n is large, some tools are helpful

x<-rnorm(30,1,2) # generate 30 random samples from Normal with
                 # mean=1, variance=4.
par(mfrow=c(2,2)); # set up graphic configuration

hist(x);boxplot(x);plot(density(x));
qqnorm(x);qqline(x);

# Keep in mind what you expect to see if normality does hold
# and what the main deviation is.

# There are other more advanced methods and tests. Nonetheless, 
# graphical tools are always helpful and easy to make understood.