# edps 587
# Spring 2019
# c.j.anderson
#
# Introduction:  NELS data --- 2 schools

setwd("D:\\Dropbox\\edps587\\\\Lectures\\1 introduction")

nels <- read.csv("nels_data.csv",header=TRUE,sep=",")
nels <- na.omit(nels)


# Pull out data for schools 24725 and 62821
nels1 <- nels[ which(nels$sch_id==24725 | nels$sch_id==62821), ]

# plot points for 2 schools
plot(nels1$homework,nels1$math, type="p", pch=19,
     main=expression(paste("NELS Data (sub-set) ")),
	 xlab="Time Spent Doing Homework",
	 ylab="Math Scores",
	 xlim=c(0,7),
	 ylim=c(20,80)
	 )
abline(lm(nels1$math ~ nels1$homework),col="blue",lwd=2)
summary(lm1<- lm(nels1$math ~ nels1$homework))
text(19,47.5, "math = 47.97 + 3.49*homework",cex=1.25)


# plot points for 2 schools w/ jitter
plot(jitter(nels$homework),nels$math, type="p", pch=19,
     main=expression(paste("NELS Data (sub-set) with some Horizondent Jittering")),
	 xlab="Time Spent Doing Homework",
	 ylab="Math Scores",
	 xlim=c(0,7),
	 ylim=c(20,80)
	 )
abline(lm(nels1$math ~ nels1$homework),col="blue",lwd=2)
summary(lm1<- lm(nels1$math ~ nels1$homework))
text(19,47.5, "math = 47.97 + 3.49*homework",cex=1.25)



##########################################
# Idenify schools in graph               #
##########################################

nels.s1 <- nels[ which(nels$sch_id==24725), ]

nels.s2 <- nels[ which(nels$sch_id==62821), ]


# Graph to illustrate need for random intercept and slope
# -- create frame for plot, notice that type='n' for none 
par(new=FALSE)
plot(jitter(nels.s1$homework),nels.s1$math,
	type="p", pch=19,
	col="blue",
	lwd=2,
	main="NELS: Linear Regression by School",
	xlab="Time Spent Doing Homework",
	ylab="Math Scores",
	xlim=c(0,7),
	ylim=c(20,80)
	)
abline(lm(math ~ homework,data=nels.s1),col="blue")
par(new=TRUE)
plot(jitter(nels.s2$homework),nels.s2$math,type="p",
    pch=19,
	col="red",
	xlab="Time Spent Doing Homework",
	ylab="Math Scores",
	xlim=c(0,7),
	ylim=c(20,80)
)
abline(lm(math ~ homework,data=nels.s2),col="red",pch=19)
legend(0, 80, legend=c("School 62821","School 24725"), 
       col=c("red","blue"), lty=1, cex=1.1,
       box.lty=1, box.lwd=1)