IQ and behavior problem

#
# An R script for IQ_Beh data set
#

#
dta <- read.table("/Users/fightk/Desktop/IQ_Beh.txt", header = T, row.names = 1)

#
str(dta)

## 'data.frame':    94 obs. of  3 variables:
##  $ Dep: Factor w/ 2 levels "D","N": 2 2 2 2 1 2 2 2 2 2 ...
##  $ IQ : int  103 124 124 104 96 92 124 99 92 116 ...
##  $ BP : int  4 12 9 3 3 3 6 4 3 9 ...

#
head(dta)

##   Dep  IQ BP
## 1   N 103  4
## 2   N 124 12
## 3   N 124  9
## 4   N 104  3
## 5   D  96  3
## 6   N  92  3

#
class(dta)

## [1] "data.frame"

#
dim(dta)

## [1] 94  3

#
names(dta)

## [1] "Dep" "IQ"  "BP"

#
is.vector(dta$BP)

## [1] TRUE

#
dta[1, ]

##   Dep  IQ BP
## 1   N 103  4

#
dta[1:3, "IQ"]

## [1] 103 124 124

#
tail(dta[order(dta$BP), ])

##    Dep  IQ BP
## 16   N  89 11
## 58   N 117 11
## 66   N 126 11
## 2    N 124 12
## 73   D  99 13
## 12   D  22 17

#
tail(dta[order(-dta$BP), ], 4)

##    Dep  IQ BP
## 77   N 124  1
## 80   N 121  1
## 24   N 106  0
## 75   N 122  0

#
with(dta, hist(IQ, xlab = "IQ", main = ""))

#
boxplot(BP ~ Dep, data = dta, 
        xlab = "Depression", 
        ylab = "Behavior problem score")

#
plot(IQ ~ BP, data = dta, pch = 20, col = dta$Dep, 
     xlab = "Behavior problem score", ylab = "IQ")
grid()

#
plot(BP ~ IQ, data = dta, type = "n",
     ylab = "Behavior problem score", xlab = "IQ")
text(dta$IQ, dta$BP, labels = dta$Dep, cex = 0.5)
abline(lm(BP ~ IQ, data = dta, subset = Dep == "D"))
abline(lm(BP ~ IQ, data = dta, subset = Dep == "N"), lty = 2)

#
t.test(IQ ~ Dep, data = dta)

## 
##  Welch Two Sample t-test
## 
## data:  IQ by Dep
## t = -1.6374, df = 15.53, p-value = 0.1216
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -26.926586   3.490299
## sample estimates:
## mean in group D mean in group N 
##        101.0667        112.7848

#
lm(BP ~ IQ, data = dta)

## 
## Call:
## lm(formula = BP ~ IQ, data = dta)
## 
## Coefficients:
## (Intercept)           IQ  
##    13.18280     -0.06792

## end