Buildrng the Regression Model I: Model Selection and Validation
Getting data
surgicalData <- read.table("http://users.stat.ufl.edu/~rrandles/sta4210/Rclassnotes/data/textdatasets/KutnerData/Chapter%20%209%20Data%20Sets/CH09TA01.txt", sep ="" , header = FALSE)
#Look at the first 6 entries
head(surgicalData) V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
1 6.7 62 81 2.59 50 0 1 0 695 6.544
2 5.1 59 66 1.70 39 0 0 0 403 5.999
3 7.4 57 83 2.16 55 0 0 0 710 6.565
4 6.5 73 41 2.01 48 0 0 0 349 5.854
5 7.8 65 115 4.30 45 0 0 1 2343 7.759
6 5.8 38 72 1.42 65 1 1 0 348 5.852 X1 X2 X3 X4 X5 X6 X7 X8 Y lnY
1 6.7 62 81 2.59 50 0 1 0 695 6.544
2 5.1 59 66 1.70 39 0 0 0 403 5.999
3 7.4 57 83 2.16 55 0 0 0 710 6.565
4 6.5 73 41 2.01 48 0 0 0 349 5.854
5 7.8 65 115 4.30 45 0 0 1 2343 7.759
6 5.8 38 72 1.42 65 1 1 0 348 5.852For simplicity we only use first four explanatory variable and first 54 of the 108 patients.
Stem and Leaf plots for individual X variables
Box plots for individual X variables
Correlation Matrix
First order regression model
The plot suggests that both curvature and nonconstant error variance are apparent. In addition, some departure from normality is suggested by the normal probability plot of residuals.
To make the distribution of the error terms more nearly normal and to see if the same transformation would also reduce the apparent curvature, the investigator examined the logarithmic transformation \(Y' = ln Y\).
Regression model with transformed Y
Now the plots look better!
Scatter Plot Matrix and Correlation Matrix when Response Variable is lnY
lnY X1 X2 X3 X4
lnY 1.0000000 0.24618787 0.46994325 0.65388548 0.6492627
X1 0.2461879 1.00000000 0.09011973 -0.14963411 0.5024157
X2 0.4699432 0.09011973 1.00000000 -0.02360544 0.3690256
X3 0.6538855 -0.14963411 -0.02360544 1.00000000 0.4164245
X4 0.6492627 0.50241567 0.36902563 0.41642451 1.0000000
All of these plots indicate that each of the predictor variables is Linearly associated with lnY , with X3 and X4 showing the highest degrees of association and X1 the lowest.
The scatter plot matrix and the correlation matrix further show intercorrelations among the potential predictor variables. In particular, X4 has moderately high pairwise correlations with __________ __________ __________ .
Plot with \(r^2\)
X1 X2 X3 X4 X5 X6 X7 X8 Y lnY
1 6.7 62 81 2.59 50 0 1 0 695 6.544
2 5.1 59 66 1.70 39 0 0 0 403 5.999
3 7.4 57 83 2.16 55 0 0 0 710 6.565
4 6.5 73 41 2.01 48 0 0 0 349 5.854
5 7.8 65 115 4.30 45 0 0 1 2343 7.759
6 5.8 38 72 1.42 65 1 1 0 348 5.852
7 5.7 46 63 1.91 49 1 0 1 518 6.250
8 3.7 68 81 2.57 69 1 1 0 749 6.619
9 6.0 67 93 2.50 58 0 1 0 1056 6.962
10 3.7 76 94 2.40 48 0 1 0 968 6.875
11 6.3 84 83 4.13 37 0 1 0 745 6.613
12 6.7 51 43 1.86 57 0 1 0 257 5.549
13 5.8 96 114 3.95 63 1 0 0 1573 7.361
14 5.8 83 88 3.95 52 1 0 0 858 6.754
15 7.7 62 67 3.40 58 0 0 1 702 6.554
16 7.4 74 68 2.40 64 1 1 0 809 6.695
17 6.0 85 28 2.98 36 1 1 0 682 6.526
18 3.7 51 41 1.55 39 0 0 0 205 5.321
19 7.3 68 74 3.56 59 1 0 0 550 6.309
20 5.6 57 87 3.02 63 0 0 1 838 6.731
21 5.2 52 76 2.85 39 0 0 0 359 5.883
22 3.4 83 53 1.12 67 1 1 0 353 5.866
23 6.7 26 68 2.10 30 0 0 1 599 6.395
24 5.8 67 86 3.40 49 1 1 0 562 6.332
25 6.3 59 100 2.95 36 1 1 0 651 6.478
26 5.8 61 73 3.50 62 1 1 0 751 6.621
27 5.2 52 86 2.45 70 0 1 0 545 6.302
28 11.2 76 90 5.59 58 1 0 1 1965 7.583
29 5.2 54 56 2.71 44 1 0 0 477 6.167
30 5.8 76 59 2.58 61 1 1 0 600 6.396
31 3.2 64 65 0.74 53 0 1 0 443 6.094
32 8.7 45 23 2.52 68 0 1 0 181 5.198
33 5.0 59 73 3.50 57 0 1 0 411 6.019
34 5.8 72 93 3.30 39 1 0 1 1037 6.944
35 5.4 58 70 2.64 31 1 1 0 482 6.179
36 5.3 51 99 2.60 48 0 1 0 634 6.453
37 2.6 74 86 2.05 45 0 0 0 678 6.519
38 4.3 8 119 2.85 65 1 0 0 362 5.893
39 4.8 61 76 2.45 51 1 1 0 637 6.457
40 5.4 52 88 1.81 40 1 0 0 705 6.558
41 5.2 49 72 1.84 46 0 0 0 536 6.283
42 3.6 28 99 1.30 55 0 0 1 582 6.366
43 8.8 86 88 6.40 30 1 1 0 1270 7.147
44 6.5 56 77 2.85 41 0 1 0 538 6.288
45 3.4 77 93 1.48 69 0 1 0 482 6.178
46 6.5 40 84 3.00 54 1 1 0 611 6.416
47 4.5 73 106 3.05 47 1 1 0 960 6.867
48 4.8 86 101 4.10 35 1 0 1 1300 7.170
49 5.1 67 77 2.86 66 1 0 0 581 6.365
50 3.9 82 103 4.55 50 0 1 0 1078 6.983
51 6.6 77 46 1.95 50 0 1 0 405 6.005
52 6.4 85 40 1.21 58 0 0 1 579 6.361
53 6.4 59 85 2.33 63 0 1 0 550 6.310
54 8.8 78 72 3.20 56 0 0 0 651 6.478subsets <- regsubsets(x = surgicalData[1:4], y = surgicalData[,10], which = "rsq", nbest = 4) #nbest: number of subsets of each size to record
summary(subsets)Subset selection object
4 Variables (and intercept)
Forced in Forced out
X1 FALSE FALSE
X2 FALSE FALSE
X3 FALSE FALSE
X4 FALSE FALSE
4 subsets of each size up to 4
Selection Algorithm: exhaustive
X1 X2 X3 X4
1 ( 1 ) " " " " "*" " "
1 ( 2 ) " " " " " " "*"
1 ( 3 ) " " "*" " " " "
1 ( 4 ) "*" " " " " " "
2 ( 1 ) " " "*" "*" " "
2 ( 2 ) " " " " "*" "*"
2 ( 3 ) "*" " " "*" " "
2 ( 4 ) " " "*" " " "*"
3 ( 1 ) "*" "*" "*" " "
3 ( 2 ) " " "*" "*" "*"
3 ( 3 ) "*" " " "*" "*"
3 ( 4 ) "*" "*" " " "*"
4 ( 1 ) "*" "*" "*" "*"
### Using leaps
obj <- leaps(x = surgicalData[1:4], y = surgicalData[,10], method = c( "r2"), nbest = 4) #nbest: number of subsets of each size to record
obj$which
1 2 3 4
1 FALSE FALSE TRUE FALSE
1 FALSE FALSE FALSE TRUE
1 FALSE TRUE FALSE FALSE
1 TRUE FALSE FALSE FALSE
2 FALSE TRUE TRUE FALSE
2 FALSE FALSE TRUE TRUE
2 TRUE FALSE TRUE FALSE
2 FALSE TRUE FALSE TRUE
3 TRUE TRUE TRUE FALSE
3 FALSE TRUE TRUE TRUE
3 TRUE FALSE TRUE TRUE
3 TRUE TRUE FALSE TRUE
4 TRUE TRUE TRUE TRUE
$label
[1] "(Intercept)" "1" "2" "3" "4"
$size
[1] 2 2 2 2 3 3 3 3 4 4 4 4 5
$r2
[1] 0.42756622 0.42154199 0.22084666 0.06060847 0.66328986 0.59948374
[7] 0.54863462 0.48296742 0.75729185 0.71781636 0.61212320 0.48701249
[13] 0.75921083 [,1] [,2]
[1,] 2 0.42756622
[2,] 2 0.42154199
[3,] 2 0.22084666
[4,] 2 0.06060847
[5,] 3 0.66328986
[6,] 3 0.59948374
[7,] 3 0.54863462
[8,] 3 0.48296742
[9,] 4 0.75729185
[10,] 4 0.71781636
[11,] 4 0.61212320
[12,] 4 0.48701249
[13,] 5 0.75921083 X1 X2
1 2 0.42756622
2 2 0.42154199
3 2 0.22084666
4 2 0.06060847
5 3 0.66328986
6 3 0.59948374
7 3 0.54863462
8 3 0.48296742
9 4 0.75729185
10 4 0.71781636
11 4 0.61212320
12 4 0.48701249
13 5 0.75921083 p r2
1 2 0.42756622
2 2 0.42154199
3 2 0.22084666
4 2 0.06060847
5 3 0.66328986
6 3 0.59948374
7 3 0.54863462
8 3 0.48296742
9 4 0.75729185
10 4 0.71781636
11 4 0.61212320
12 4 0.48701249
13 5 0.75921083# A tibble: 4 × 2
p mr2
<dbl> <dbl>
1 2 0.428
2 3 0.663
3 4 0.757
4 5 0.759ggplot(data = tab, aes(x=p, y=r2)) + geom_point(color = "red") +
geom_line(data = tabmax, aes(x=p, y=mr2), color = "blue") + theme_bw()
1 2 3 4
1 2 0.42756622 0 0 1 0
1 2 0.42154199 0 0 0 1
1 2 0.22084666 0 1 0 0
1 2 0.06060847 1 0 0 0
2 3 0.66328986 0 1 1 0
2 3 0.59948374 0 0 1 1
2 3 0.54863462 1 0 1 0
2 3 0.48296742 0 1 0 1
3 4 0.75729185 1 1 1 0
3 4 0.71781636 0 1 1 1
3 4 0.61212320 1 0 1 1
3 4 0.48701249 1 1 0 1
4 5 0.75921083 1 1 1 1Plot with \(R^2_{adj}\)
subsets <- regsubsets(x = surgicalData[1:4], y = surgicalData[,10], which = "adjr2", nbest = 4) #nbest: number of subsets of each size to record
summary(subsets)## Subset selection object
## 4 Variables (and intercept)
## Forced in Forced out
## X1 FALSE FALSE
## X2 FALSE FALSE
## X3 FALSE FALSE
## X4 FALSE FALSE
## 4 subsets of each size up to 4
## Selection Algorithm: exhaustive
## X1 X2 X3 X4
## 1 ( 1 ) " " " " "*" " "
## 1 ( 2 ) " " " " " " "*"
## 1 ( 3 ) " " "*" " " " "
## 1 ( 4 ) "*" " " " " " "
## 2 ( 1 ) " " "*" "*" " "
## 2 ( 2 ) " " " " "*" "*"
## 2 ( 3 ) "*" " " "*" " "
## 2 ( 4 ) " " "*" " " "*"
## 3 ( 1 ) "*" "*" "*" " "
## 3 ( 2 ) " " "*" "*" "*"
## 3 ( 3 ) "*" " " "*" "*"
## 3 ( 4 ) "*" "*" " " "*"
## 4 ( 1 ) "*" "*" "*" "*"
### Using leaps
obj <- leaps(x = surgicalData[1:4], y = surgicalData[,10], method = c("adjr2"), nbest = 4) # only change the method from previous criterion
obj## $which
## 1 2 3 4
## 1 FALSE FALSE TRUE FALSE
## 1 FALSE FALSE FALSE TRUE
## 1 FALSE TRUE FALSE FALSE
## 1 TRUE FALSE FALSE FALSE
## 2 FALSE TRUE TRUE FALSE
## 2 FALSE FALSE TRUE TRUE
## 2 TRUE FALSE TRUE FALSE
## 2 FALSE TRUE FALSE TRUE
## 3 TRUE TRUE TRUE FALSE
## 3 FALSE TRUE TRUE TRUE
## 3 TRUE FALSE TRUE TRUE
## 3 TRUE TRUE FALSE TRUE
## 4 TRUE TRUE TRUE TRUE
##
## $label
## [1] "(Intercept)" "1" "2" "3" "4"
##
## $size
## [1] 2 2 2 2 3 3 3 3 4 4 4 4 5
##
## $adjr2
## [1] 0.41655788 0.41041780 0.20586294 0.04254324 0.65008554 0.58377722
## [7] 0.53093401 0.46269163 0.74272936 0.70088534 0.58885059 0.45623323
## [13] 0.73955457## X1 X2
## 1 2 0.41655788
## 2 2 0.41041780
## 3 2 0.20586294
## 4 2 0.04254324
## 5 3 0.65008554
## 6 3 0.58377722
## 7 3 0.53093401
## 8 3 0.46269163
## 9 4 0.74272936
## 10 4 0.70088534
## 11 4 0.58885059
## 12 4 0.45623323
## 13 5 0.73955457## p adjr2
## 1 2 0.41655788
## 2 2 0.41041780
## 3 2 0.20586294
## 4 2 0.04254324
## 5 3 0.65008554
## 6 3 0.58377722
## 7 3 0.53093401
## 8 3 0.46269163
## 9 4 0.74272936
## 10 4 0.70088534
## 11 4 0.58885059
## 12 4 0.45623323
## 13 5 0.73955457## # A tibble: 4 × 2
## p madjr2
## <dbl> <dbl>
## 1 2 0.417
## 2 3 0.650
## 3 4 0.743
## 4 5 0.740ggplot(data = tab, aes(x=p, y=adjr2)) + geom_point(color = "red") +
geom_line(data = tabmax, aes(x=p, y=madjr2), color = "blue") + theme_bw()
## 1 2 3 4
## 1 2 0.41655788 0 0 1 0
## 1 2 0.41041780 0 0 0 1
## 1 2 0.20586294 0 1 0 0
## 1 2 0.04254324 1 0 0 0
## 2 3 0.65008554 0 1 1 0
## 2 3 0.58377722 0 0 1 1
## 2 3 0.53093401 1 0 1 0
## 2 3 0.46269163 0 1 0 1
## 3 4 0.74272936 1 1 1 0
## 3 4 0.70088534 0 1 1 1
## 3 4 0.58885059 1 0 1 1
## 3 4 0.45623323 1 1 0 1
## 4 5 0.73955457 1 1 1 1## 1 2 3 4
## 4.0000000 0.7427294 1.0000000 1.0000000 1.0000000 0.0000000Plot with \(C_p\)
subsets <- regsubsets(x = surgicalData[1:4], y = surgicalData[,10], which = "cp", nbest = 4) #nbest: number of subsets of each size to record
summary(subsets)## Subset selection object
## 4 Variables (and intercept)
## Forced in Forced out
## X1 FALSE FALSE
## X2 FALSE FALSE
## X3 FALSE FALSE
## X4 FALSE FALSE
## 4 subsets of each size up to 4
## Selection Algorithm: exhaustive
## X1 X2 X3 X4
## 1 ( 1 ) " " " " "*" " "
## 1 ( 2 ) " " " " " " "*"
## 1 ( 3 ) " " "*" " " " "
## 1 ( 4 ) "*" " " " " " "
## 2 ( 1 ) " " "*" "*" " "
## 2 ( 2 ) " " " " "*" "*"
## 2 ( 3 ) "*" " " "*" " "
## 2 ( 4 ) " " "*" " " "*"
## 3 ( 1 ) "*" "*" "*" " "
## 3 ( 2 ) " " "*" "*" "*"
## 3 ( 3 ) "*" " " "*" "*"
## 3 ( 4 ) "*" "*" " " "*"
## 4 ( 1 ) "*" "*" "*" "*"
### Using leaps
obj <- leaps(x = surgicalData[1:4], y = surgicalData[,10], method = c( "Cp"), nbest = 4)
obj## $which
## 1 2 3 4
## 1 FALSE FALSE TRUE FALSE
## 1 FALSE FALSE FALSE TRUE
## 1 FALSE TRUE FALSE FALSE
## 1 TRUE FALSE FALSE FALSE
## 2 FALSE TRUE TRUE FALSE
## 2 FALSE FALSE TRUE TRUE
## 2 TRUE FALSE TRUE FALSE
## 2 FALSE TRUE FALSE TRUE
## 3 TRUE TRUE TRUE FALSE
## 3 FALSE TRUE TRUE TRUE
## 3 TRUE FALSE TRUE TRUE
## 3 TRUE TRUE FALSE TRUE
## 4 TRUE TRUE TRUE TRUE
##
## $label
## [1] "(Intercept)" "1" "2" "3" "4"
##
## $size
## [1] 2 2 2 2 3 3 3 3 4 4 4 4 5
##
## $Cp
## [1] 66.488856 67.714773 108.555776 141.163851 20.519679 33.504067
## [7] 43.851738 57.214850 3.390508 11.423673 32.931969 58.391689
## [13] 5.000000## X1 X2
## 1 2 66.488856
## 2 2 67.714773
## 3 2 108.555776
## 4 2 141.163851
## 5 3 20.519679
## 6 3 33.504067
## 7 3 43.851738
## 8 3 57.214850
## 9 4 3.390508
## 10 4 11.423673
## 11 4 32.931969
## 12 4 58.391689
## 13 5 5.000000## p Cp
## 1 2 66.488856
## 2 2 67.714773
## 3 2 108.555776
## 4 2 141.163851
## 5 3 20.519679
## 6 3 33.504067
## 7 3 43.851738
## 8 3 57.214850
## 9 4 3.390508
## 10 4 11.423673
## 11 4 32.931969
## 12 4 58.391689
## 13 5 5.000000## # A tibble: 4 × 2
## p mCp
## <dbl> <dbl>
## 1 2 66.5
## 2 3 20.5
## 3 4 3.39
## 4 5 5.00ggplot(data = tab, aes(x=p, y=Cp)) + geom_point(color = "red") +
geom_line(data = tabmax, aes(x=p, y=mCp), color = "blue") + theme_bw()
## 1 2 3 4
## 1 2 66.488856 0 0 1 0
## 1 2 67.714773 0 0 0 1
## 1 2 108.555776 0 1 0 0
## 1 2 141.163851 1 0 0 0
## 2 3 20.519679 0 1 1 0
## 2 3 33.504067 0 0 1 1
## 2 3 43.851738 1 0 1 0
## 2 3 57.214850 0 1 0 1
## 3 4 3.390508 1 1 1 0
## 3 4 11.423673 0 1 1 1
## 3 4 32.931969 1 0 1 1
## 3 4 58.391689 1 1 0 1
## 4 5 5.000000 1 1 1 1## 1 2 3 4
## 4.000000 3.390508 1.000000 1.000000 1.000000 0.000000Multiple Criterians at once
##
## Attaching package: 'olsrr'## The following object is masked from 'package:datasets':
##
## rivers## Index N Predictors R-Square Adj. R-Square Mallow's Cp
## 3 1 1 X3 0.42756622 0.41655788 66.488856
## 4 2 1 X4 0.42154199 0.41041780 67.714773
## 2 3 1 X2 0.22084666 0.20586294 108.555776
## 1 4 1 X1 0.06060847 0.04254324 141.163851
## 8 5 2 X2 X3 0.66328986 0.65008554 20.519679
## 10 6 2 X3 X4 0.59948374 0.58377722 33.504067
## 6 7 2 X1 X3 0.54863462 0.53093401 43.851738
## 9 8 2 X2 X4 0.48296742 0.46269163 57.214850
## 7 9 2 X1 X4 0.43010550 0.40775670 67.972119
## 5 10 2 X1 X2 0.26273627 0.23382397 102.031343
## 11 11 3 X1 X2 X3 0.75729185 0.74272936 3.390508
## 14 12 3 X2 X3 X4 0.71781636 0.70088534 11.423673
## 13 13 3 X1 X3 X4 0.61212320 0.58885059 32.931969
## 12 14 3 X1 X2 X4 0.48701249 0.45623323 58.391689
## 15 15 4 X1 X2 X3 X4 0.75921083 0.73955457 5.000000
Best subsets algorithms
library(olsrr)
# To obtain the set of plots in page 362
surgicalModelAll <- lm(lnY ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data = surgicalData)
summary(surgicalModelAll)##
## Call:
## lm(formula = lnY ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data = surgicalData)
##
## Residuals:
## Min 1Q Median 3Q Max
## -0.35562 -0.13833 -0.05158 0.14949 0.46472
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 4.050515 0.251756 16.089 < 2e-16 ***
## X1 0.068512 0.025422 2.695 0.00986 **
## X2 0.013452 0.001947 6.909 1.39e-08 ***
## X3 0.014954 0.001809 8.264 1.43e-10 ***
## X4 0.008016 0.046708 0.172 0.86450
## X5 -0.003566 0.002752 -1.296 0.20163
## X6 0.084208 0.060750 1.386 0.17253
## X7 0.057864 0.067483 0.857 0.39574
## X8 0.388383 0.088380 4.394 6.69e-05 ***
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 0.2093 on 45 degrees of freedom
## Multiple R-squared: 0.8461, Adjusted R-squared: 0.8188
## F-statistic: 30.93 on 8 and 45 DF, p-value: 7.8e-16## Index N Predictors R-Square Adj. R-Square Mallow's Cp
## 3 1 1 X3 0.42756622 0.416557881 117.409441
## 4 2 1 X4 0.42154199 0.410417798 119.171240
## 2 3 1 X2 0.22084666 0.205862939 177.865004
## 8 4 1 X8 0.13896492 0.122406556 201.811487
## 1 5 1 X1 0.06060847 0.042543244 224.726995
## 6 6 1 X6 0.05384893 0.035653717 226.703835
## 5 7 1 X5 0.02101436 0.002187716 236.306372
## 7 8 1 X7 0.01602435 -0.002898254 237.765710
## 16 9 2 X2 X3 0.66328986 0.650085544 50.471575
## 22 10 2 X3 X4 0.59948374 0.583777218 69.131808
## 10 11 2 X1 X3 0.54863462 0.530934014 84.002738
## 26 12 2 X3 X8 0.51638460 0.497419295 93.434321
## 30 13 2 X4 X8 0.50782098 0.488519841 95.938771
## 17 14 2 X2 X4 0.48296742 0.462691631 103.207247
## 24 15 2 X3 X6 0.44775235 0.426095576 113.505967
## 23 16 2 X3 X5 0.44620869 0.424491387 113.957411
## 29 17 2 X4 X7 0.43393030 0.411731492 117.548252
## 25 18 2 X3 X7 0.43263981 0.410390386 117.925661
## 11 19 2 X1 X4 0.43010550 0.407756700 118.666823
## 28 20 2 X4 X6 0.42329987 0.400684181 120.657144
## 27 21 2 X4 X5 0.42165329 0.398973031 121.138689
## 21 22 2 X2 X8 0.39189208 0.368044713 129.842416
## 9 23 2 X1 X2 0.26273627 0.233823967 167.614301
## 20 24 2 X2 X7 0.25601115 0.226835112 169.581077
## 19 25 2 X2 X6 0.25149268 0.222139448 170.902513
## 18 26 2 X2 X5 0.23590259 0.205937984 175.461866
## 35 27 2 X6 X8 0.20396789 0.172750941 184.801236
## 15 28 2 X1 X8 0.16681363 0.134139660 195.667073
## 33 29 2 X5 X8 0.14968015 0.116334270 200.677798
## 36 30 2 X7 X8 0.14467058 0.111128255 202.142854
## 13 31 2 X1 X6 0.10980148 0.074891738 212.340395
## 12 32 2 X1 X5 0.08018051 0.044109155 221.003110
## 31 33 2 X5 X6 0.07525635 0.038991895 222.443190
## 34 34 2 X6 X7 0.07251794 0.036146098 223.244043
## 14 35 2 X1 X7 0.07129317 0.034873293 223.602231
## 32 36 2 X5 X7 0.03228060 -0.005669181 235.011538
## 62 37 3 X2 X3 X8 0.77803373 0.764715749 18.914496
## 37 38 3 X1 X2 X3 0.75729185 0.742729360 24.980500
## 58 39 3 X2 X3 X4 0.71781636 0.700885337 36.525190
## 61 40 3 X2 X3 X7 0.68096045 0.661818074 47.303776
## 59 41 3 X2 X3 X5 0.67614248 0.656711027 48.712801
## 60 42 3 X2 X3 X6 0.66972707 0.649910695 50.589000
## 76 43 3 X3 X4 X8 0.66912072 0.649267958 50.766330
## 43 44 3 X1 X3 X4 0.61212320 0.588850588 67.435372
## 75 45 3 X3 X4 X7 0.60535901 0.581680554 69.413572
## 73 46 3 X3 X4 X5 0.60155797 0.577651443 70.525196
## 74 47 3 X3 X4 X6 0.60063138 0.576669264 70.796177
## 47 48 3 X1 X3 X8 0.59664418 0.572442836 71.962241
## 66 49 3 X2 X4 X8 0.59317780 0.568768468 72.975993
## 44 50 3 X1 X3 X5 0.56517531 0.539085831 81.165378
## 45 51 3 X1 X3 X6 0.56298658 0.536765778 81.805477
## 46 52 3 X1 X3 X7 0.54971929 0.522702446 85.685524
## 81 53 3 X3 X6 X8 0.54387486 0.516507349 87.394740
## 51 54 3 X1 X4 X8 0.53044387 0.502270499 91.322661
## 79 55 3 X3 X5 X8 0.52714735 0.498776188 92.286735
## 82 56 3 X3 X7 X8 0.52510928 0.496615835 92.882773
## 87 57 3 X4 X6 X8 0.51307031 0.483854533 96.403593
## 88 58 3 X4 X7 X8 0.50998468 0.480583760 97.305993
## 85 59 3 X4 X5 X8 0.50807180 0.478556112 97.865417
## 65 60 3 X2 X4 X7 0.50515075 0.475459798 98.719685
## 38 61 3 X1 X2 X4 0.48701249 0.456233235 104.024258
## 64 62 3 X2 X4 X6 0.48439147 0.453454963 104.790778
## 63 63 3 X2 X4 X5 0.48330696 0.452305382 105.107946
## 77 64 3 X3 X5 X6 0.46669524 0.434696949 109.966080
## 80 65 3 X3 X6 X7 0.45402812 0.421269809 113.670604
## 78 66 3 X3 X5 X7 0.44886096 0.415792619 115.181750
## 50 67 3 X1 X4 X7 0.44472680 0.411410409 116.390794
## 86 68 3 X4 X6 X7 0.43621403 0.402386869 118.880372
## 84 69 3 X4 X5 X7 0.43396561 0.400003551 119.537925
## 49 70 3 X1 X4 X6 0.43102308 0.396884467 120.398475
## 71 71 3 X2 X6 X8 0.43036308 0.396184860 120.591495
## 48 72 3 X1 X4 X5 0.43010752 0.395913975 120.666232
## 83 73 3 X4 X5 X6 0.42348475 0.388893836 122.603075
## 42 74 3 X1 X2 X8 0.40425587 0.368511225 128.226601
## 69 75 3 X2 X5 X8 0.39746072 0.361308360 130.213858
## 72 76 3 X2 X7 X8 0.39259800 0.356153882 131.635969
## 40 77 3 X1 X2 X6 0.29118358 0.248654593 161.294827
## 41 78 3 X1 X2 X7 0.29036093 0.247782585 161.535412
## 70 79 3 X2 X6 X7 0.28851309 0.245823876 162.075816
## 39 80 3 X1 X2 X5 0.27697980 0.233598586 165.448752
## 67 81 3 X2 X5 X6 0.26706319 0.223086986 168.348883
## 68 82 3 X2 X5 X7 0.26493872 0.220835044 168.970189
## 56 83 3 X1 X6 X8 0.22721230 0.180845035 180.003360
## 90 84 3 X5 X6 X8 0.21463019 0.167508001 183.683023
## 92 85 3 X6 X7 X8 0.20915415 0.161703395 185.284503
## 54 86 3 X1 X5 X8 0.17769501 0.128356714 194.484792
## 57 87 3 X1 X7 X8 0.17196881 0.122286939 196.159432
## 91 88 3 X5 X7 X8 0.15726864 0.106704756 200.458528
## 52 89 3 X1 X5 X6 0.12979185 0.077579363 208.494170
## 55 90 3 X1 X6 X7 0.12278427 0.070151328 210.543552
## 89 91 3 X5 X6 X7 0.08873885 0.034063177 220.500207
## 53 92 3 X1 X5 X7 0.08716732 0.032397357 220.959803
## 97 93 4 X1 X2 X3 X8 0.82988400 0.815996984 5.750774
## 131 94 4 X2 X3 X4 X8 0.81444134 0.799293694 10.267014
## 136 95 4 X2 X3 X6 X8 0.78876213 0.771518218 17.776952
## 134 96 4 X2 X3 X5 X8 0.78356252 0.765894154 19.297588
## 137 97 4 X2 X3 X7 X8 0.77995759 0.761994941 20.351858
## 94 98 4 X1 X2 X3 X5 0.76887693 0.750009741 23.592419
## 96 99 4 X1 X2 X3 X7 0.76649685 0.747435371 24.288478
## 95 100 4 X1 X2 X3 X6 0.76135339 0.741872034 25.792694
## 93 101 4 X1 X2 X3 X4 0.75921083 0.739554570 26.419290
## 130 102 4 X2 X3 X4 X7 0.73293141 0.711129897 34.104759
## 128 103 4 X2 X3 X4 X5 0.72177867 0.699066722 37.366403
## 129 104 4 X2 X3 X4 X6 0.71851944 0.695541433 38.319572
## 133 105 4 X2 X3 X5 X7 0.68975331 0.664427047 46.732286
## 135 106 4 X2 X3 X6 X7 0.68828952 0.662843767 47.160374
## 132 107 4 X2 X3 X5 X6 0.68283811 0.656947338 48.754651
## 153 108 4 X3 X4 X7 X8 0.67374296 0.647109728 51.414546
## 152 109 4 X3 X4 X6 X8 0.67293201 0.646232581 51.651710
## 111 110 4 X1 X3 X4 X8 0.67144798 0.644627405 52.085717
## 150 111 4 X3 X4 X5 X8 0.66953109 0.642554036 52.646315
## 116 112 4 X1 X3 X6 X8 0.61673165 0.585444440 68.087620
## 108 113 4 X1 X3 X4 X5 0.61616796 0.584834732 68.252473
## 110 114 4 X1 X3 X4 X7 0.61574513 0.584377382 68.376131
## 109 115 4 X1 X3 X4 X6 0.61456936 0.583105630 68.719988
## 101 116 4 X1 X2 X4 X8 0.60837935 0.576410314 70.530269
## 114 117 4 X1 X3 X5 X8 0.60769916 0.575674602 70.729191
## 151 118 4 X3 X4 X6 X7 0.60680757 0.574710232 70.989937
## 149 119 4 X3 X4 X5 X7 0.60651769 0.574396688 71.074714
## 117 120 4 X1 X3 X7 X8 0.60446866 0.572180384 71.673958
## 148 121 4 X3 X4 X5 X6 0.60294038 0.570527347 72.120907
## 142 122 4 X2 X4 X6 X8 0.59832171 0.565531642 73.471646
## 143 123 4 X2 X4 X7 X8 0.59363981 0.560467552 74.840876
## 140 124 4 X2 X4 X5 X8 0.59328136 0.560079837 74.945707
## 112 125 4 X1 X3 X5 X6 0.57981300 0.545512016 78.884557
## 113 126 4 X1 X3 X5 X7 0.56537611 0.529896606 83.106655
## 115 127 4 X1 X3 X6 X7 0.56463256 0.529092365 83.324106
## 155 128 4 X3 X5 X6 X8 0.55460080 0.518241677 86.257917
## 157 129 4 X3 X6 X7 X8 0.55204340 0.515475516 87.005832
## 156 130 4 X3 X5 X7 X8 0.53819681 0.500498585 91.055298
## 122 131 4 X1 X4 X6 X8 0.53357952 0.495504377 92.405633
## 123 132 4 X1 X4 X7 X8 0.53259174 0.494435968 92.694510
## 120 133 4 X1 X4 X5 X8 0.53158918 0.493351559 92.987713
## 161 134 4 X4 X6 X7 X8 0.51523987 0.475667618 97.769100
## 159 135 4 X4 X5 X6 X8 0.51319753 0.473458556 98.366387
## 100 136 4 X1 X2 X4 X7 0.51093403 0.471010279 99.028353
## 160 137 4 X4 X5 X7 X8 0.51009251 0.470100058 99.274459
## 141 138 4 X2 X4 X6 X7 0.50719957 0.466970959 100.120505
## 139 139 4 X2 X4 X5 X7 0.50516062 0.464765563 100.716800
## 99 140 4 X1 X2 X4 X6 0.48790530 0.446101649 105.763153
## 98 141 4 X1 X2 X4 X5 0.48715464 0.445289709 105.982686
## 138 142 4 X2 X4 X5 X6 0.48483977 0.442785875 106.659673
## 154 143 4 X3 X5 X6 X7 0.47022848 0.426981824 110.932776
## 121 144 4 X1 X4 X6 X7 0.44596325 0.400735755 118.029193
## 119 145 4 X1 X4 X5 X7 0.44505096 0.399748996 118.295993
## 106 146 4 X1 X2 X6 X8 0.44087433 0.395231417 119.517457
## 158 147 4 X4 X5 X6 X7 0.43622212 0.390199434 120.878006
## 145 148 4 X2 X5 X6 X8 0.43610769 0.390075662 120.911471
## 147 149 4 X2 X6 X7 X8 0.43104657 0.384601390 122.391606
## 118 150 4 X1 X4 X5 X6 0.43103933 0.384593556 122.393724
## 104 151 4 X1 X2 X5 X8 0.41001507 0.361853036 128.542311
## 107 152 4 X1 X2 X7 X8 0.40489454 0.356314504 130.039821
## 146 153 4 X2 X5 X7 X8 0.39870369 0.349618273 131.850349
## 105 154 4 X1 X2 X6 X7 0.32061032 0.265149937 154.688915
## 102 155 4 X1 X2 X5 X6 0.30593119 0.249272512 158.981857
## 103 156 4 X1 X2 X5 X7 0.29930989 0.242110694 160.918271
## 144 157 4 X2 X5 X6 X7 0.29770259 0.240372187 161.388329
## 125 158 4 X1 X5 X6 X8 0.23802809 0.175826301 178.840259
## 127 159 4 X1 X6 X7 X8 0.23193438 0.169235145 180.622377
## 162 160 4 X5 X6 X7 X8 0.22161023 0.158068213 183.641695
## 126 161 4 X1 X5 X7 X8 0.18465576 0.118097046 194.449107
## 124 162 4 X1 X5 X6 X7 0.13864225 0.068327335 207.905852
## 171 163 5 X1 X2 X3 X6 X8 0.83744126 0.820508061 5.540639
## 169 164 5 X1 X2 X3 X5 X8 0.83580826 0.818704958 6.018212
## 166 165 5 X1 X2 X3 X4 X8 0.83313992 0.815758658 6.798576
## 172 166 5 X1 X2 X3 X7 X8 0.83167542 0.814141607 7.226872
## 202 167 5 X2 X3 X4 X6 X8 0.81788212 0.798911508 11.260750
## 203 168 5 X2 X3 X4 X7 X8 0.81594726 0.796775100 11.826604
## 200 169 5 X2 X3 X4 X5 X8 0.81566233 0.796460487 11.909933
## 205 170 5 X2 X3 X5 X6 X8 0.79438537 0.772967184 18.132422
## 207 171 5 X2 X3 X6 X7 X8 0.79062800 0.768818413 19.231275
## 206 172 5 X2 X3 X5 X7 X8 0.78633272 0.764075717 20.487436
## 168 173 5 X1 X2 X3 X5 X7 0.77531394 0.751909146 23.709901
## 167 174 5 X1 X2 X3 X5 X6 0.77314833 0.749517945 24.343240
## 170 175 5 X1 X2 X3 X6 X7 0.77116415 0.747327077 24.923518
## 163 176 5 X1 X2 X3 X4 X5 0.76908567 0.745032092 25.531373
## 165 177 5 X1 X2 X3 X4 X7 0.76885947 0.744782335 25.597525
## 164 178 5 X1 X2 X3 X4 X6 0.76214345 0.737366725 27.561640
## 199 179 5 X2 X3 X4 X5 X7 0.73495391 0.707344937 35.513278
## 201 180 5 X2 X3 X4 X6 X7 0.73401319 0.706306235 35.788391
## 198 181 5 X2 X3 X4 X5 X6 0.72273768 0.693856183 39.085940
## 204 182 5 X2 X3 X5 X6 X7 0.69720963 0.665668966 46.551669
## 216 183 5 X3 X4 X6 X7 X8 0.67754959 0.643961003 52.301289
## 188 184 5 X1 X3 X4 X7 X8 0.67627657 0.642555380 52.673586
## 187 185 5 X1 X3 X4 X6 X8 0.67601873 0.642270684 52.748991
## 215 186 5 X3 X4 X5 X7 X8 0.67457994 0.640682020 53.169768
## 214 187 5 X3 X4 X5 X6 X8 0.67351159 0.639502381 53.482210
## 185 188 5 X1 X3 X4 X5 X8 0.67232795 0.638195447 53.828367
## 190 189 5 X1 X3 X5 X6 X8 0.62774183 0.588964941 66.867670
## 192 190 5 X1 X3 X6 X7 X8 0.62414055 0.584988524 67.920873
## 183 191 5 X1 X3 X4 X5 X6 0.61926220 0.579602015 69.347555
## 184 192 5 X1 X3 X4 X5 X7 0.61860448 0.578875783 69.539907
## 186 193 5 X1 X3 X4 X6 X7 0.61840093 0.578651025 69.599437
## 191 194 5 X1 X3 X5 X7 X8 0.61775534 0.577938188 69.788240
## 177 195 5 X1 X2 X4 X6 X8 0.61177573 0.571335697 71.536991
## 175 196 5 X1 X2 X4 X5 X8 0.60901545 0.568287894 72.344239
## 178 197 5 X1 X2 X4 X7 X8 0.60887957 0.568137857 72.383978
## 213 198 5 X3 X4 X5 X6 X7 0.60814052 0.567321819 72.600116
## 211 199 5 X2 X4 X6 X7 X8 0.59878708 0.556994067 75.335547
## 209 200 5 X2 X4 X5 X6 X8 0.59835369 0.556515537 75.462292
## 210 201 5 X2 X4 X5 X7 X8 0.59369913 0.551376123 76.823529
## 189 202 5 X1 X3 X5 X6 X7 0.58028658 0.536566431 80.746057
## 217 203 5 X3 X5 X6 X7 X8 0.56501667 0.519705905 85.211774
## 196 204 5 X1 X4 X6 X7 X8 0.53573260 0.487371409 93.775961
## 194 205 5 X1 X4 X5 X6 X8 0.53445535 0.485961112 94.149495
## 195 206 5 X1 X4 X5 X7 X8 0.53340375 0.484799976 94.457037
## 218 207 5 X4 X5 X6 X7 X8 0.51527319 0.464780813 99.759357
## 176 208 5 X1 X2 X4 X6 X7 0.51223908 0.461430646 100.646690
## 174 209 5 X1 X2 X4 X5 X7 0.51108042 0.460151296 100.985541
## 208 210 5 X2 X4 X5 X6 X7 0.50719961 0.455866234 102.120493
## 173 211 5 X1 X2 X4 X5 X6 0.48811657 0.434795382 107.701366
## 180 212 5 X1 X2 X5 X6 X8 0.44679328 0.389167576 119.786449
## 193 213 5 X1 X4 X5 X6 X7 0.44619513 0.388507123 119.961378
## 182 214 5 X1 X2 X6 X7 X8 0.44149715 0.383319773 121.335311
## 212 215 5 X2 X5 X6 X7 X8 0.43732990 0.378718435 122.554032
## 181 216 5 X1 X2 X5 X7 X8 0.41117687 0.349841124 130.202541
## 179 217 5 X1 X2 X5 X6 X7 0.32981166 0.260000371 153.997965
## 197 218 5 X1 X5 X6 X7 X8 0.24447620 0.165775801 178.954497
## 226 219 6 X1 X2 X3 X5 X6 X8 0.84343626 0.823449402 5.787389
## 228 220 6 X1 X2 X3 X6 X7 X8 0.83918918 0.818660139 7.029456
## 223 221 6 X1 X2 X3 X4 X6 X8 0.83872170 0.818132982 7.166172
## 227 222 6 X1 X2 X3 X5 X7 X8 0.83844803 0.817824375 7.246207
## 221 223 6 X1 X2 X3 X4 X5 X8 0.83714610 0.816356244 7.626958
## 224 224 6 X1 X2 X3 X4 X7 X8 0.83479488 0.813704868 8.314578
## 243 225 6 X2 X3 X4 X6 X7 X8 0.81938834 0.796331530 12.820254
## 241 226 6 X2 X3 X4 X5 X6 X8 0.81937072 0.796311668 12.825405
## 242 227 6 X2 X3 X4 X5 X7 X8 0.81754448 0.794252288 13.359493
## 244 228 6 X2 X3 X5 X6 X7 X8 0.79709267 0.771189602 19.340669
## 225 229 6 X1 X2 X3 X5 X6 X7 0.78008280 0.752008264 24.315239
## 220 230 6 X1 X2 X3 X4 X5 X7 0.77581462 0.747195207 25.563478
## 219 231 6 X1 X2 X3 X4 X5 X6 0.77316271 0.744204756 26.339035
## 222 232 6 X1 X2 X3 X4 X6 X7 0.77218459 0.743101776 26.625086
## 240 233 6 X2 X3 X4 X5 X6 X7 0.73623378 0.702561492 37.138977
## 237 234 6 X1 X3 X4 X6 X7 X8 0.68087463 0.640135221 53.328874
## 246 235 6 X3 X4 X5 X6 X7 X8 0.67862460 0.637597958 53.986898
## 236 236 6 X1 X3 X4 X5 X7 X8 0.67781288 0.636682605 54.224290
## 235 237 6 X1 X3 X4 X5 X6 X8 0.67727606 0.636077263 54.381282
## 238 238 6 X1 X3 X5 X6 X7 X8 0.63731987 0.591020282 66.066552
## 234 239 6 X1 X3 X4 X5 X6 X7 0.62179533 0.573513886 70.606736
## 232 240 6 X1 X2 X4 X6 X7 X8 0.61227672 0.562780136 73.390473
## 230 241 6 X1 X2 X4 X5 X6 X8 0.61220642 0.562700859 73.411033
## 231 242 6 X1 X2 X4 X5 X7 X8 0.60939705 0.559532848 74.232638
## 245 243 6 X2 X4 X5 X6 X7 X8 0.59879690 0.547579483 77.332675
## 239 244 6 X1 X4 X5 X6 X7 X8 0.53631780 0.477124325 95.604818
## 229 245 6 X1 X2 X4 X5 X6 X7 0.51232412 0.450067624 102.621819
## 233 246 6 X1 X2 X5 X6 X7 X8 0.44794155 0.377466003 121.450634
## 251 247 7 X1 X2 X3 X5 X6 X7 X8 0.84602791 0.822597377 7.029455
## 248 248 7 X1 X2 X3 X4 X5 X6 X8 0.84361461 0.819816836 7.735230
## 250 249 7 X1 X2 X3 X4 X6 X7 X8 0.84038662 0.816097625 8.679263
## 249 250 7 X1 X2 X3 X4 X5 X7 X8 0.83955867 0.815143680 8.921400
## 254 251 7 X2 X3 X4 X5 X6 X7 X8 0.82129305 0.794098517 14.263216
## 247 252 7 X1 X2 X3 X4 X5 X6 X7 0.78009570 0.746632006 26.311466
## 253 253 7 X1 X3 X4 X5 X6 X7 X8 0.68291063 0.634657905 54.733440
## 252 254 7 X1 X2 X4 X5 X6 X7 X8 0.61260940 0.553658658 75.293181
## 255 255 8 X1 X2 X3 X4 X5 X6 X7 X8 0.84612863 0.818773720 9.000000
# To get the table 9.3
library(leaps)
obj <- regsubsets(x = surgicalData[1:8], y = surgicalData[,10], nbest = 1, which = "adjr2")
objSummary <- summary(obj)
objSummary## Subset selection object
## 8 Variables (and intercept)
## Forced in Forced out
## X1 FALSE FALSE
## X2 FALSE FALSE
## X3 FALSE FALSE
## X4 FALSE FALSE
## X5 FALSE FALSE
## X6 FALSE FALSE
## X7 FALSE FALSE
## X8 FALSE FALSE
## 1 subsets of each size up to 8
## Selection Algorithm: exhaustive
## X1 X2 X3 X4 X5 X6 X7 X8
## 1 ( 1 ) " " " " "*" " " " " " " " " " "
## 2 ( 1 ) " " "*" "*" " " " " " " " " " "
## 3 ( 1 ) " " "*" "*" " " " " " " " " "*"
## 4 ( 1 ) "*" "*" "*" " " " " " " " " "*"
## 5 ( 1 ) "*" "*" "*" " " " " "*" " " "*"
## 6 ( 1 ) "*" "*" "*" " " "*" "*" " " "*"
## 7 ( 1 ) "*" "*" "*" " " "*" "*" "*" "*"
## 8 ( 1 ) "*" "*" "*" "*" "*" "*" "*" "*"## [1] 0.4165579 0.6500855 0.7647157 0.8159970 0.8205081 0.8234494 0.8225974
## [8] 0.8187737obj <- regsubsets(x = surgicalData[1:8], y = surgicalData[,10], nbest = 1, which = "cp")
objSummary <- summary(obj)
objSummary## Subset selection object
## 8 Variables (and intercept)
## Forced in Forced out
## X1 FALSE FALSE
## X2 FALSE FALSE
## X3 FALSE FALSE
## X4 FALSE FALSE
## X5 FALSE FALSE
## X6 FALSE FALSE
## X7 FALSE FALSE
## X8 FALSE FALSE
## 1 subsets of each size up to 8
## Selection Algorithm: exhaustive
## X1 X2 X3 X4 X5 X6 X7 X8
## 1 ( 1 ) " " " " "*" " " " " " " " " " "
## 2 ( 1 ) " " "*" "*" " " " " " " " " " "
## 3 ( 1 ) " " "*" "*" " " " " " " " " "*"
## 4 ( 1 ) "*" "*" "*" " " " " " " " " "*"
## 5 ( 1 ) "*" "*" "*" " " " " "*" " " "*"
## 6 ( 1 ) "*" "*" "*" " " "*" "*" " " "*"
## 7 ( 1 ) "*" "*" "*" " " "*" "*" "*" "*"
## 8 ( 1 ) "*" "*" "*" "*" "*" "*" "*" "*"## [1] 117.409441 50.471575 18.914496 5.750774 5.540639 5.787389 7.029455
## [8] 9.000000obj <- regsubsets(x = surgicalData[1:8], y = surgicalData[,10], nbest = 1, which = "rss")
objSummary <- summary(obj)
objSummary## Subset selection object
## 8 Variables (and intercept)
## Forced in Forced out
## X1 FALSE FALSE
## X2 FALSE FALSE
## X3 FALSE FALSE
## X4 FALSE FALSE
## X5 FALSE FALSE
## X6 FALSE FALSE
## X7 FALSE FALSE
## X8 FALSE FALSE
## 1 subsets of each size up to 8
## Selection Algorithm: exhaustive
## X1 X2 X3 X4 X5 X6 X7 X8
## 1 ( 1 ) " " " " "*" " " " " " " " " " "
## 2 ( 1 ) " " "*" "*" " " " " " " " " " "
## 3 ( 1 ) " " "*" "*" " " " " " " " " "*"
## 4 ( 1 ) "*" "*" "*" " " " " " " " " "*"
## 5 ( 1 ) "*" "*" "*" " " " " "*" " " "*"
## 6 ( 1 ) "*" "*" "*" " " "*" "*" " " "*"
## 7 ( 1 ) "*" "*" "*" " " "*" "*" "*" "*"
## 8 ( 1 ) "*" "*" "*" "*" "*" "*" "*" "*"## [1] 7.331575 4.312491 2.842883 2.178799 2.082008 2.005225 1.972032 1.970742Forward Stepwise Regression
fit <- lm(lnY ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data = surgicalData) # Full Model
o <- step(fit, direction = "forward") ## Start: AIC=-160.77
## lnY ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8##
## Call:
## lm(formula = lnY ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data = surgicalData)
##
## Residuals:
## Min 1Q Median 3Q Max
## -0.35562 -0.13833 -0.05158 0.14949 0.46472
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 4.050515 0.251756 16.089 < 2e-16 ***
## X1 0.068512 0.025422 2.695 0.00986 **
## X2 0.013452 0.001947 6.909 1.39e-08 ***
## X3 0.014954 0.001809 8.264 1.43e-10 ***
## X4 0.008016 0.046708 0.172 0.86450
## X5 -0.003566 0.002752 -1.296 0.20163
## X6 0.084208 0.060750 1.386 0.17253
## X7 0.057864 0.067483 0.857 0.39574
## X8 0.388383 0.088380 4.394 6.69e-05 ***
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 0.2093 on 45 degrees of freedom
## Multiple R-squared: 0.8461, Adjusted R-squared: 0.8188
## F-statistic: 30.93 on 8 and 45 DF, p-value: 7.8e-16Model Validation
# Get the Validation set
surgicalDataValidation <- read.table("http://users.stat.ufl.edu/~rrandles/sta4210/Rclassnotes/data/textdatasets/KutnerData/Chapter%20%209%20Data%20Sets/CH09TA05.txt", sep ="" , header = FALSE)
names(surgicalDataValidation) <- c(paste("X", 1:8, sep = ""), "Y" , "lnY")
dim(surgicalDataValidation)## [1] 54 10#------------------------------------------------------------------------------------
# We selected X1, X2, X3, X6, X8 using Cp criterion in the earlier section
lmCpVal <- lm(lnY ~ X1 + X2 + X3 + X6 + X8, data = surgicalDataValidation)
summary(lmCpVal)##
## Call:
## lm(formula = lnY ~ X1 + X2 + X3 + X6 + X8, data = surgicalDataValidation)
##
## Residuals:
## Min 1Q Median 3Q Max
## -0.57757 -0.13516 0.01021 0.13439 0.49539
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 3.614319 0.290665 12.435 < 2e-16 ***
## X1 0.099885 0.032295 3.093 0.0033 **
## X2 0.015910 0.002374 6.702 2.1e-08 ***
## X3 0.015447 0.002042 7.566 1.0e-09 ***
## X6 0.073091 0.079154 0.923 0.3604
## X8 0.188575 0.096622 1.952 0.0568 .
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 0.2787 on 48 degrees of freedom
## Multiple R-squared: 0.7115, Adjusted R-squared: 0.6815
## F-statistic: 23.68 on 5 and 48 DF, p-value: 6.482e-12## [1] 0.07768364## [1] 0.681457#names(summary(lmCpVal))
#------------------------------------------------------------------------------------
# We selected X1, X2, X3, X5, X6, X8 using R2adj criterion in the earlier section
lmRVal <- lm(lnY ~ X1 + X2 + X3 + X5 + X6 + X8, data = surgicalDataValidation)
summary(lmRVal)##
## Call:
## lm(formula = lnY ~ X1 + X2 + X3 + X5 + X6 + X8, data = surgicalDataValidation)
##
## Residuals:
## Min 1Q Median 3Q Max
## -0.60092 -0.12580 0.01123 0.13493 0.49742
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 3.469928 0.346781 10.006 3.14e-13 ***
## X1 0.098737 0.032466 3.041 0.00385 **
## X2 0.016203 0.002414 6.712 2.23e-08 ***
## X3 0.015582 0.002058 7.572 1.12e-09 ***
## X5 0.002540 0.003293 0.771 0.44443
## X6 0.072651 0.079493 0.914 0.36542
## X8 0.193054 0.097206 1.986 0.05288 .
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 0.2799 on 47 degrees of freedom
## Multiple R-squared: 0.7151, Adjusted R-squared: 0.6787
## F-statistic: 19.66 on 6 and 47 DF, p-value: 2.525e-11## [1] 0.07834499## [1] 0.6787451#------------------------------------------------------------------------------------
# Making a table so it is easier to compre the models
compare <- data.frame(matrix(c(MSPR1, MSPR2, adjRsq1, adjRsq2), ncol = 2, byrow = TRUE))
colnames(compare) <- c( "Model 1" , "Model 2")
rownames(compare) <- c( "MSPR" , "Adj R square")
compare## Model 1 Model 2
## MSPR 0.07768364 0.07834499
## Adj R square 0.68145696 0.67874506