#######################################################################
#
# Dataset: Grade Point Average (GPA)
#
#######################################################################
#
# Summary: Data on 4,137 US college students.
#
#  1. sat                       combined SAT score
#  2. tothrs                   total hours through fall semest
#  3. colgpa                 GPA after fall semester
#  4. athlete                 =1 if athlete
#  5. verbmath             verbal/math SAT score
#  6. hsize                    size graduating class, 100s
#  7. hsrank                  rank in graduating class
#  8. hsperc                 100*(hsrank/hssize)
#  9. female                  =1 if female
# 10. white                   =1 if white
# 11. black                   =1 if black
# 12. hsizesq               hsize^2
#
# colgpa is measured on a four-point scale
# hsperc is the percentile in the high school graduating class (defined so that, for
# example, hsperc 5 5 means the top 5% of the class)
# sat is the combined math and verbal scores on the student achievement test.
#
#######################################################################
#
# Source: Wooldridge (2012) 
# Introductory Econometrics: A Modern Approach (5th edition)
# South-Western, Cengage Learning
#
#######################################################################
#
# Copyright of R code by:
#
# Hedibert Freitas Lopes 
# Professor of Statistics and Econometrics
# Insper - Institute for Education and Research
#
#######################################################################

data = matrix(scan("gpa2-wooldridge.txt"),ncol=12,byrow=TRUE)

colgpa = data[,3]
hsperc = data[,8]
sat    = data[,1]
athlete = data[,4]
female = data[,9]
black  = data[,11]

reg = lm(colgpa~sat)
summary(reg)
reg = lm(colgpa~sat+athlete)
summary(reg)
reg = lm(colgpa~sat+female)
summary(reg)
reg = lm(colgpa~sat+black)
summary(reg)
reg = lm(colgpa~athlete)
summary(reg)
reg = lm(colgpa~female)
summary(reg)
reg = lm(colgpa~black)
summary(reg)

reg = lm(colgpa~athlete+female)
summary(reg)
reg = lm(colgpa~black+female)
summary(reg)
reg = lm(colgpa~athlete+black)
summary(reg)


reg = lm(sat~athlete)
summary(reg)
reg = lm(sat~female)
summary(reg)
reg = lm(sat~black)
summary(reg)
reg = lm(sat~athlete+female)
summary(reg)
reg = lm(sat~black+female)
summary(reg)
reg = lm(sat~athlete+black)
summary(reg)


par(mfrow=c(2,3))
hist(colgpa)
hist(sat)
hist(hsperc)
plot(sat,colgpa)
plot(hsperc,colgpa)
plot(sat,hsperc)