Hw-6.pdf - hw6 Mingyu Sun 4/22/2020 problem 1 part a) make...

hw6
Mingyu Sun
4/22/2020
problem 1
part a) make plots of the data
library (faraway)
data (butterfat)
attach (butterfat)
par ( mfrow= c ( 2 , 2 ))
boxplot (Butterfat ~ Breed, data= butterfat, outline= FALSE )
stripchart (Butterfat ~ Breed, data= butterfat, method= "jitter" ,
col= "blue" , vertical= TRUE , add= TRUE )
boxplot (Butterfat ~ Age, data= butterfat, outline= FALSE )
stripchart (Butterfat ~ Age, data= butterfat, method= "jitter" ,
col= "blue" , vertical= TRUE , add= TRUE )
interaction.plot (butterfat $ Breed,butterfat $ Age,butterfat $ Butterfat)
interaction.plot (butterfat $ Age,butterfat $ Breed,butterfat $ Butterfat)
1

Ayrshire Guernsey Jersey
3.5
5.0
6.5
Breed
Butterfat
2year Mature
3.5
5.0
6.5
Age
Butterfat
4.0
5.0
butterfat$Breed
mean of
butterfat$Butterfat
Ayrshire Guernsey Jersey
butterfat$Ag
Matur
2year
4.0
5.0
butterfat$Age
mean of
butterfat$Butterfat
2year Mature
butterfat$Breed
Jersey
Guernse
Canadian
Ayrshire
Holstein-
part b)
model= lm (Butterfat ~ Breed * Age, data= butterfat)
anova (model)
## Analysis of Variance Table
##
## Response: Butterfat
## Df Sum Sq Mean Sq F value Pr(>F)
## Breed 4 34.321 8.5803 49.5651 <2e-16 ***
## Age 1 0.274 0.2735 1.5801 0.2120
## Breed:Age 4 0.514 0.1285 0.7421 0.5658
## Residuals 90 15.580 0.1731
## ---
## Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1
2

P value of the anova test for the interaction term is 0.5658. Therefore, Do Not
reject H0. Interaction term is not significant. This can also be seen from the
interaction plots. Since the lines are almost parallel to each other, the interaction