NOTE: For your homework download and use the template (https://math.dartmouth.edu/~m50f17/HW5.Rmd)
Read the green comments in the rmd file to see where your answers should go.
You can use qqnorm and qqline functions to plot probability plots of residuals. The functions rstandard and rstudent calculate the standardized residuals and R-student residuals, respectively.
prop = read.table("https://math.dartmouth.edu/~m50f17/propellant.csv", header=T, sep=",")
age <- prop$Age
shearS <- prop$ShearS
fitted = lm(shearS ~ age)
stdRes = rstandard(fitted)
rStuRes = rstudent(fitted)
qqnorm(rStuRes, main="Normal Probability Plot (residuals on vertical axis)")
qqline(rStuRes)
However, note that the book uses residuals on the x-axis instead of y-axis. In order to obtain that use the parameter datax as shown below. In the below graph x-axis denotes the R-student residuals and the y-axis is the theoretical quantiles ( in the book y-axis is probability instead of quantiles).
qqnorm(rStuRes, datax = TRUE ,
main="Normal Probability Plot")
qqline(rStuRes, datax = TRUE )
yHat <- predict(fitted)
plot (yHat, rStuRes)
abline(0,0)
After observing that the observation points 5 and 6 look like potential outliers, next we delete those points and compare the fitted model of the deleted data with the full data.
plot(age, shearS, xlim=c(0,30), ylim=c(1600,2700))
abline(fitted$coef, lwd = 2, col = "blue")
ageRem <- age[-6]
ageRem <- ageRem[-5]
shearSRem <- shearS[-6]
shearSRem <- shearSRem[-5]
fitted2 = lm(shearSRem ~ ageRem)
abline(fitted2$coef, lwd = 2, col = "red")
There is a dedicated library :
MPV: Data Sets from Montgomery, Peck and Vining’s Book
in order to provide an easy way to load tables from the book. To install the library type :
install.packages(“MPV”)
Below is an example how to use this library. Check https://cran.r-project.org/web/packages/MPV/MPV.pdf for table names.
library(MPV)
##
## Attaching package: 'MPV'
## The following object is masked from 'package:datasets':
##
## stackloss
data(table.b1)
y <- table.b1$y
x1 <- table.b1$x1
x3 <- table.b1$x3
x8 <- table.b1$x8
y.lm <- lm(y ~ x1 + x3 + x8)
summary(y.lm)
##
## Call:
## lm(formula = y ~ x1 + x3 + x8)
##
## Residuals:
## Min 1Q Median 3Q Max
## -3.6835 -1.5609 -0.1448 1.7188 4.0386
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 12.136744 9.145612 1.327 0.19698
## x1 0.001123 0.001938 0.580 0.56762
## x3 0.159582 0.296318 0.539 0.59516
## x8 -0.006496 0.002088 -3.112 0.00475 **
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 2.42 on 24 degrees of freedom
## Multiple R-squared: 0.5702, Adjusted R-squared: 0.5164
## F-statistic: 10.61 on 3 and 24 DF, p-value: 0.0001244
Solve the parts (a), (b) and (c) of Problem 4.1. In addition answer the following.
Chapter 4, Problem 2 all parts.
Chapter 4, Problem 19 all parts. In addition answer the following.