Stat 305: Regression Handout:
Example 1:
Stress / Till-till-fracture data. In the following data,
x= uniaxial stress applied (kg/mm2) and y = time till fracture (hours)
x
y
2.5
63
5
58
10
55
15
61
17.5
62
20
37
25
38
30
45
35
46
40
19
We will fit a linear and quadratic model on this data using least square methods.
JMP Handout:
x
2.5
5
10
15
17.5
20
25
30
35
40
y
63
58
55
61
62
37
38
45
46
19
Predicted y
64.165486726
61.913274336
57.408849558
52.904424779
50.652212389
48.4
43.895575221
39.391150442
34.886725664
30.382300885
Residual y
-1.165486726
-3.913274336
-2.408849558
8.0955752212
11.347787611
-11.4
-5.895575221
5.6088495575
11.113274336
-11.38230088
Response y
Whole Model
Regression Plot
60
y
50
40
30
20
0
5
10
15
20
25
30
35
40
45
x
Summary of Fit
RSquare
RSquare Adj
Root Mean Square Error
Mean of Response
Observations (or Sum Wgts)
Analysis of Variance
Source
DF
Model
Error
C. Total
1
8
9
0.632518
0.586583
9.124307
48.4
10
Sum of
Squares
1146.3761
666.0239
1812.4000
Mean Square
F Ratio
1146.38
83.25
13.7698
Prob > F
0.0059*
Parameter Estimates
Term
Estimate
Std Error
t Ratio
Prob>|t|
Intercept
66.417699
5.648129
11.76
<.0001*
x
-0.900885
0.242776
-3.71
0.0059*
Residual by Predicted Plot
10
y Residual
5
0
-5
-10
20
30
40
50
60
y Predicted
Prediction Expression
Y=
66.4176991150442
+ -0.9008849557522
*x
Quadratic Model with x and x^2:
Response y
Whole Model
Actual by Predicted Plot
60
y Actual
50
40
30
20
20
30
40
50
60
y Predicted P=0.0233
RSq=0.66 RMSE=9.4035
Summary of Fit
RSquare
RSquare Adj
Root Mean Square Error
Mean of Response
Observations (or Sum Wgts)
Analysis of Variance
Source
DF
Model
Error
C. Total
2
7
9
0.658473
0.560894
9.403518
48.4
10
Sum of
Squares
1193.4169
618.9831
1812.4000
Parameter Estimates
Term
Estimate
Intercept
61.52298
x
-0.208514
xsq
-0.016541
Std Error
8.883684
0.981695
0.022678
Mean Square
F Ratio
596.708
88.426
6.7481
Prob > F
0.0233*
t Ratio
6.93
-0.21
-0.73
Prob>|t|
0.0002*
0.8378
0.4895
Residual by Predicted Plot
15
10
y Residual
5
0
-5
-10
-15
20
30
40
50
60
y Predicted
Prediction Expression:
Y=
61.5229796176377
+ -0.2085138825891
*x
+ -0.0165407888515
* xsq
Example 2:
Data collected on a hardness study of a particular alloy. The variables are:
x1= % of copper in alloy, x2 = tempering temperature and y = hardness
x1
x2
y
0.02
1000 78.9
1100 65.1
1200 55.2
1300 56.4
0.1
1000 80.9
1100 69.7
1200 57.4
1300 55.4
0.18
1000 85.3
1100 71.8
1200 60.7
1300 58.9
We will fit a linear model and some variations on this data using least square methods.
Model with x1 and x2:
Response y
Whole Model
Actual by Predicted Plot
90
85
y Actual
80
75
70
65
60
55
50
55
60
65
70
75
80
85
90
y Predicted P<.0001
RSq=0.90 RMSE=3.7909
Summary of Fit
RSquare
RSquare Adj
Root Mean Square Error
Mean of Response
Observations (or Sum Wgts)
Analysis of Variance
Source
DF
Model
Error
C. Total
2
9
11
0.899073
0.876645
3.790931
66.30833
12
Sum of
Squares
1152.1888
129.3404
1281.5292
Parameter Estimates
Term
Estimate
Intercept
161.33646
x1
32.96875
x2
-0.0855
Std Error
11.43285
16.75371
0.009788
Mean Square
F Ratio
576.094
14.371
40.0868
Prob > F
<.0001*
t Ratio
14.11
1.97
-8.74
Prob>|t|
<.0001*
0.0806
<.0001*
Prediction Expression
Y=
161.336458333333
+ 32.96875
+ -0.0855
* x1
* x2
Distributions
Residual y
6
-1.28
-0.67
0.0
0.67
1.28
4
2
0
-2
-4
-6
0.1
0.2
0.3 0.4 0.5
Normal Quantile Plot
Bivariate Fit of Residual y By x1
6
4
Residual y
2
0
-2
-4
-6
0
0.05
0.1
x1
0.15
0.2
0.7
0.8
0.9
Bivariate Fit of Residual y By x2
6
4
Residual y
2
0
-2
-4
-6
950
1000
1050
1150
1100
1200
1250
1300
x2
Bivariate Fit of Residual y By Predicted y
6
4
Residual y
2
0
-2
-4
-6
50
55
60
65
Predicted y
70
75
80
85
Output with x1, x2 and x2^2 in the model.
Response y
Whole Model
Actual by Predicted Plot
90
85
y Actual
80
75
70
65
60
55
50
55
60
65
70
75
80
85
90
y Predicted P<.0001
RSq=0.98 RMSE=1.656
Summary of Fit
RSquare
RSquare Adj
Root Mean Square Error
Mean of Response
Observations (or Sum Wgts)
Analysis of Variance
Source
DF
Model
Error
C. Total
3
8
11
0.98288
0.97646
1.656034
66.30833
12
Sum of
Squares
1259.5896
21.9396
1281.5292
Parameter Estimates
Term
Estimate
Intercept
553.24479
x1
32.96875
x2
-0.773583
x2-sq
0.0002992
Std Error
62.82414
7.318705
0.110036
4.781e-5
Mean Square
F Ratio
419.863
2.742
153.0980
Prob > F
<.0001*
t Ratio
8.81
4.50
-7.03
6.26
Prob>|t|
<.0001*
0.0020*
0.0001*
0.0002*
Residual by Predicted Plot
3
y Residual
2
1
0
-1
-2
50
55
60
65
75
70
80
85
90
y Predicted
Prediction Expression
553.244791666667
+ 32.96875
* x1
+ -0.7735833333333
* x2
+ 0.00029916666667
* x2-sq
Residuals:
3
Residual y 2
2
1
0
-1
-2
0
0.05
0.1
x1
Linear Fit
0.15
0.2
3
Residual y2
2
1
0
-1
-2
950
1000
1050
1100
1150
x2
Linear Fit
1200
1250
1300